https://www.coastalwiki.org/w/api.php?action=feedcontributions&user=Ltherry&feedformat=atomCoastal Wiki - User contributions [en]2024-03-28T14:24:59ZUser contributionsMediaWiki 1.31.7https://www.coastalwiki.org/w/index.php?title=Phenotype&diff=11969Phenotype2007-10-02T14:00:17Z<p>Ltherry: </p>
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<div>{{Definition|title=Phenotype<br />
|definition= the visible or otherwise measurable physical and biochemical characteristics of an organism, resulting from the interaction of genotype and environment.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Crustacea&diff=11968Crustacea2007-10-02T13:56:27Z<p>Ltherry: </p>
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<div>{{Definition|title=Crustacea, crustaceans<br />
|definition= subphylum of arthropods, considered as a class in older classifications. They are mainly aquatic, gill-breathing animals, such as crabs, lobsters and shrimps. The body is divided into a head bearing five pairs of appendages (two pairs of pre-oral sensory feelers and three pairs of post-oral feeding appendages) and a trunk and abdomen bearing a variable number of often biramous appendages wich serve as walking legs and gills. Crustacea often have a hard carapace of shell.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Bryozoan&diff=11967Bryozoan2007-10-02T13:50:02Z<p>Ltherry: </p>
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<div>{{Definition|title=Ectoprocta, ectoprocts<br />
|definition= phylum of small marine and freshwater colonial animals, which superficially resemble mosses, hence the common name of moss animals. A colony is composed of zooids each bearing a crown of ciliated tentacles (a lophophore), and living in a horny, calcareous or gelatinous case. (formerly) Bryozoa, bryozoans, Polyzoa.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Foliose&diff=11966Foliose2007-10-02T13:44:15Z<p>Ltherry: </p>
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<div>{{Definition|title=foliose<br />
|definition= having leaf-like lobes<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Ophiuroid&diff=11965Ophiuroid2007-10-02T13:41:53Z<p>Ltherry: </p>
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<div>{{Definition|title=Ophiuroidea<br />
|definition= class of echinoderms commonly known as brittle stars, having a star-shaped body with the arms clearly marked off from the central disc.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Endemic&diff=11957Endemic2007-10-02T12:11:32Z<p>Ltherry: </p>
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<div>{{Definition|title=Endemic<br />
|definition= restricted to a certain region or part of region<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Echinoderms&diff=11955Echinoderms2007-10-02T12:05:30Z<p>Ltherry: </p>
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<div>{{Definition|title=Echinodermata, echinoderms<br />
|definition= phylum of marine coelomate animals that are bilaterally symmetrical as larvae but show five-rayed symmetry as adults and have a calcareous endoskeleton and a water vascular system. It includes the classes Crinoidea (sea lilies and feater stars), Asteroidea (starfish), [[Ophiuroid|Ophiuroidea]] (brittle stars), [[Echinoid|Echinoidea]] (sea urchins) and Holothuroidea (sea cucumbers).<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Echinoid&diff=11954Echinoid2007-10-02T12:03:16Z<p>Ltherry: </p>
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<div>{{Definition|title=Echinoidea<br />
|definition= class of [[echinoderms]], commonly called sea urchins, having a typically globular body with skeletal plates fitting together to form a rigid test.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Echinoderms&diff=11953Echinoderms2007-10-02T12:02:14Z<p>Ltherry: </p>
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<div>{{Definition|title=Echinodermata, echinoderms<br />
|definition= phylum of marine coelomate animals that are bilaterally symmetrical as larvae but show five-rayed symmetry as adults and have a calcareous endoskeleton and a water vascular system. It includes the classes Crinoidea (sea lilies and feater stars), Asteroidea (starfish), [[Ophiuroidea]] (brittle stars), [[Echinoidea]] (sea urchins) and Holothuroidea (sea cucumbers).<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Echinoid&diff=11952Echinoid2007-10-02T11:57:13Z<p>Ltherry: </p>
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<div>{{Definition|title=Eninoidea<br />
|definition= class of [[echinoderms]], commonly called sea urchins, having a typically globular body with skeletal plates fitting together to form a rigid test.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Echinoid&diff=11951Echinoid2007-10-02T11:56:24Z<p>Ltherry: </p>
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<div>{{Definition|title=Eninoidea<br />
|definition= class of [[echinoderms]], commonly called sea urchins, having a typically globular body with skeletal plates fitting together to form a rigid test.<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>.}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Pluteus&diff=11950Pluteus2007-10-02T11:51:29Z<p>Ltherry: </p>
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<div>{{Definition|title=Pluteus<br />
|definition= free-swimming larval stage of sea urchins and brittle stars, characterized by long processes stiffened by tiny spicules<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>.}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11947Effects of fisheries on European marine biodiversity2007-10-02T11:40:34Z<p>Ltherry: /* Direct effects of physical disturbance */</p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived [[Functional_diversity#Classification_by_functional_feeding_mechanism|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Functional_diversity#Classification_by_functional_feeding_mechanism|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
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When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Trophic cascading effect=== <br />
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Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed [[phytoplankton]] to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
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===‘Food-web’ competition=== <br />
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[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
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Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to [[phenotypic]] variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in [[life-history traits]].<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing.<br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent [[recruitment]] to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Piscivorous&diff=11946Piscivorous2007-10-02T11:34:12Z<p>Ltherry: </p>
<hr />
<div>{{Definition|title=Piscivorous<br />
|definition= fish-eating<ref name="Hendersons"> Lawrence, E. (2005). ''Henderson’s dictionary of biology.'' Pearson Education Limited, 13th ed., Harlow. 748 p. </ref>.}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11667Effects of fisheries on European marine biodiversity2007-09-05T13:54:15Z<p>Ltherry: /* Effects on phenotypic evolution */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed [[phytoplankton]] to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to [[phenotypic]] variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in [[life-history traits]].<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing.<br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent [[recruitment]] to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11666Effects of fisheries on European marine biodiversity2007-09-05T13:52:42Z<p>Ltherry: /* Indirect effects of physical disturbance */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed [[phytoplankton]] to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to [[phenotypic]] variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in [[life-history traits]].<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing.<br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent [[recruitment]] to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11665Effects of fisheries on European marine biodiversity2007-09-05T13:51:07Z<p>Ltherry: /* Effects on phenotypic evolution */</p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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<br />
==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed [[phytoplankton]] to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to [[phenotypic]] variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in [[life-history traits]].<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing.<br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11664Effects of fisheries on European marine biodiversity2007-09-05T13:48:43Z<p>Ltherry: /* Trophic cascading effect */</p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed [[phytoplankton]] to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11663Effects of fisheries on European marine biodiversity2007-09-05T13:48:16Z<p>Ltherry: /* Trophic cascading effect */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the [[Biodiversity_in_the_European_Seas#The_Black_Sea.5B6.5D|Black Sea]], a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by [[planktivorous]] fish causes a decline in [[zooplankton]] biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref><br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11662Effects of fisheries on European marine biodiversity2007-09-05T13:46:34Z<p>Ltherry: /* Effects of ‘ghost-fishing’ */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and [[Crustacea]] attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11661Effects of fisheries on European marine biodiversity2007-09-05T13:45:33Z<p>Ltherry: /* Direct effects of physical disturbance */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the [[foliose]] [[bryozoan]] ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11660Effects of fisheries on European marine biodiversity2007-09-05T13:42:34Z<p>Ltherry: /* Direct effects of physical disturbance */</p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the [[mesozooplankton]] composition. For instance, the mesozooplankton taken in [[Continuous Plankton Recorder (CPR)|continuous plankton recorder]] samples in the central [[Biodiversity_in_the_European_Seas#The_North_Sea.5B1.5D|North Sea]] were numerically dominated by [[calanoid copepods]] from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the [[pluteus]] larvae of [[echinoid]] and [[ophiuroid]] [[echinoderms]]. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11659Effects of fisheries on European marine biodiversity2007-09-05T13:34:04Z<p>Ltherry: /* Direct effects of physical disturbance */</p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Biodiversity_in_the_European_Seas#The_Arctic_Ocean.5B4.5D|Arctic]] and [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
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When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Trophic cascading effect=== <br />
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Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
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===‘Food-web’ competition=== <br />
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[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11658Effects of fisheries on European marine biodiversity2007-09-05T13:29:17Z<p>Ltherry: /* Direct effects of physical disturbance */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived [[Suspension feeder|suspension feeders]] are most likely to be replaced by a community of opportunistic [[Deposit-feeder|deposit-feeding]] species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11657Effects of fisheries on European marine biodiversity2007-09-05T13:26:31Z<p>Ltherry: /* Direct effects on by-catch species */</p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some [[By-catch|by-catch]] species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11656Effects of fisheries on European marine biodiversity2007-09-05T13:21:39Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the [[Biodiversity_in_the_European_Seas#The_North-east_Atlantic_Ocean.5B3.5D|North Atlantic]] fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
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===‘Food-web’ competition=== <br />
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[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
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Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=By-catch&diff=11655By-catch2007-09-05T13:15:35Z<p>Ltherry: </p>
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<div>{{<br />
Definition|title=By-catch<br />
|definition= Fish and/or other marine life that are incidentally caught with the targeted species. Most of the time by-catch is discarded at sea.<br />
<ref>CoPraNet glossary [http://www.coastalpractice.net/glossary/index.htm]</ref>. <br />
}}<br />
==References==<br />
<references/></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Biodiversity_in_the_European_Seas&diff=11622Biodiversity in the European Seas2007-09-03T09:06:39Z<p>Ltherry: /* The Caspian Sea<ref name="The Caspian Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Caspian Sea''</ref> */</p>
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<div>This article acts about the [[Biodiversity_in_the_valuation_concept|biodiversity]] in the European Seas. We refer to [http://reports.eea.europa.eu/report_2002_0524_154909/en reports (publish date: 31 may 2002) of the ‘European Environmental Agency’ (visited 31/08/2007)]([[European Environmental Agency (EEA)|EEA]]), in which each Sea is treated closely with a large attention for the marine biodiversity. In the ‘EEA reports’ an overview is given of the most important physical, biological and exploitation characteristics, the main threats to biodiversity and the policies at work (nature protection and protection of marine resources by restrictions on fishing and hunting).The contents of these reports are reflected with the indication of the most relevant information.<br />
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==The North Sea<ref name="North Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The North Sea''</ref>== <br />
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[[Image:North Sea.jpg|right|300px|North Sea<ref name="North Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/NorthSea.pdf''link to actual EEA report'' (visited: 31/08/2007)]<br />
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The North Sea is a shallow sea (average depth: 90 m) with a surface area of 750 000 km². It is rather a young ecosystem formed by the flooding of a landmass some 20 000 years ago. Its coast and waters are still being colonized by new species from the Atlantic. <br />
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As main influences on the North Seas ecosystem are considered: [[Effects of fisheries on European marine biodiversity|fisheries]], [[Eutrophication|eutrophication]], offshore industry, maritime traffic, industry and tourism. <br />
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The strong coupling between [[benthic]] and [[pelagic]] communities in the shallow parts of the sea makes it extremely productive and one of the most productive areas in the world, with a wide range of [[plankton]], fish, seabirds and benthic communities. The North Sea is one of the world’s most important fishing grounds. The sea is also rich in oil and gas. Many human activities have an impact on the biodiversity of the North Sea. The marine ecosystems are under intense pressure from fishing, fish farming, kelp harvesting, invading species, nutrient input, recreational use, habitat loss and [[Effects of global climate change on European marine biodiversity|climate changes]]; most notable are the effects of fisheries and eutrophication.<br />
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The policy conducted in the North Sea has several objectives, from nature protection (discussed conventions/agreements are [[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], [[International Council for the Exploration of the Sea (ICES)|ICES]], [[Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS)|ASCOBANS]] and the [[North_Sea_pollution_from_shipping:_legal_framework#The_Bonn_Agreement|Bonn Convention]], [[Trilateral Wadden Sea Cooperation]], [[North Sea Conference]], [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]] and [[Bern Convention]]) to protection of marine resources (ASCOBANS, the EU Common Fisheries Policy ([[EU Comon Fisheries Policy (CFP)|CFP]])). <br />
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Furthermore, there are several national, international and non-governmental organization initiatives to assess environmental quality in the North Sea area. The most important are: the ‘continuous plankton recorder’ ([[Continuous Plankton Recorder (CPR)|CPR]]), [[BioMar]] an the ‘Joint assessment and monitoring programme’ ([[Joint Assessment and Monitoring Programme (JAMP)|JAMP]]). <br />
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[[Image:CPR.jpg|center|300px|Diagram showing a cutaway view of the `'''Continuous Plankton Recorder'''`(CPR) , the plankton filtering mechanism, and a photograph of the instrument. SOURCE: www.sahfos.ac.uk|frame]]<br />
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==The Baltic Sea<ref name="Baltic Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref>== <br />
[[Image:Baltic Sea.jpg|right|300px|The Baltic Sea<ref name="Baltic Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/BalticSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
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The Baltic Sea is the largest (surface area: 370 000 km²) brackish water system in the world. The shallow sounds between Sweden and Denmark provide a limited water exchange with the North Sea. It takes 25-35 years for all the water in the Baltic to be replenished by water from the North Sea and beyond.<br />
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The Baltic Sea has marked [[stratification]] between low-salinity surface water and the more saline deep water at a depth of about 40-70 m. This salinity barrier prevents the exchange of oxygen and nutrients, and large parts of the seabed are lifeless because of oxygen depletion. The vertical and horizontal salinity gradients are reflected in different species communities and species numbers. The highest biodiversity is found in the south-west of the Baltic Sea.<br />
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The Baltic Sea is slowly shrinking because of geological uplifting of land after the last glaciation.<br />
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Because of the geologically short time aspect (the Baltic Sea is formed after the last glaciation as the ice retreated some 10 000 years ago) and major changes, a very limited brackish water flora and fauna has developed. The Baltic Sea is therefore characterized by few species, but many individuals of each species.<br />
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The considered main threats to biodiversity are [[Eutrophication|eutrophication]], [[Effects of fisheries on European marine biodiversity|fisheries]], pollution of oil and contaminants, constructions and [[Effects of invasions on European marine biodiversity|introduction of non-indigenous species]]. <br />
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Nearly enclosed seas such as the Baltic are particularly sensitive to inputs of pollutants, because of the long residence time of the water (25 to 35 years). Although concentrations of most of the hazardous substances have decreased over the past 30 years in the Baltic area, a number of them are still of environmental concern, such as cadmium, dioxins and PCBs. One of the effects of contamination is sterility in a large part of the Baltic mammals population (probably due to PCB poisoning). <br />
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The discussed political instruments of application on the Baltic Sea are the Helsinki Convention of 1974 ([[The Helsinki Commission (HELCOM)|HELCOM]]), the International Baltic Sea Fishery Commission ([[International Baltic Sea Fishery Commission (IBSFC)|IBSFC]]), [[Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS)|ASCOBANS]], the [[Ramsar Convention]], [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]], the [[Bern Convention]] and [[Bird_Directive%2C_Habitat_Directive%2C_NATURA_2000#NATURA_2000|Natura 2000]].<br />
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The [[Baltic Monitoring Programme]], as part of COMBINE (Co-operative Monitoring in the Baltic Marine Environment), is implemented by the Helsinki Commission. The aims are to identify and quantify the effects of anthropogenic discharges/activities in the Baltic Sea in the context of the natural variations in the system, and to identify and quantify the changes in the environment as a result of regulatory actions.<br />
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==The North-east Atlantic Ocean<ref name="NE Atlantic"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The North-east Atlantic Ocean''</ref>== <br />
[[Image:NE Atlantic.jpg|right|300px|The North-east Atlantic Ocean<ref name="NE Atlantic"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The North-east Atlantic Ocean''</ref>|frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/nea_ocean.pdf''link to actual EEA report'' (visited 31/08/2007) ]<br />
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The North-east Atlantic Ocean is a part of the Atlantic Ocean. The morphology of the sea floor is dominated by two deep areas on both sides of the Mid Atlantic Ridge with depths down to 5 000 m and a shallow continental shelf along the European coast.<br />
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The formation of the North Atlantic deep water is one of the driving forces for the thermohaline circulation of the world’s oceans. The water flow is predominantly from west to east.<br />
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The primary productivity in the open ocean is low, but is increasing from south to north and towards shore. Cold-water reefs with ''Lophelia pertusa'' as the main reef building species are present along the coasts of the whole area. In deep water outside Scotland and Ireland there are large areas covered by cold water corals formed by two species, ''Lophelia pertusa'' and ''Madrepora oculata'', which interconnect with tubes of the worm ''Eunice norvegicus''. These deep-water reefs have a high biodiversity. <br />
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As main threats to biodiversity in the North-east Atlantic Ocean are considered: [[Effects of global climate change on European marine biodiversity|climatic changes]], [[Effects of fisheries on European marine biodiversity|fisheries]], mariculture, [[Effects of invasions on European marine biodiversity|introduced species]], [[Eutrophication|eutrophication]] and pollution of oil and contaminants. The biodiversity is high, but several species in the area are endangered of which lack of sustainable fishery management is probably the most important threat. Eutrophication is not regarded as a problem for this sea except for some local coastal areas, mainly estuaries in the Celtic sea and some estuaries along the coast of Biscay.<br />
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[[International Council for the Exploration of the Sea (ICES)|ICES]](1996) indicates that there is a need for a 40 % reduction in the fishing fleet to avoid over-fishing and match available fish resources. Most of the commercial fish stocks are outside ‘safe biological limit’ in the Atlantic area (OSPAR, 2000; EEA, 2002) including cod, hake, saithe, plaice, sole, sardine, anglerfish and megrims. <br />
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Several legal instruments aim to protect and conserve the marine life in the North-east Atlantic Ocean: ([[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], ICES, [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]], North Atlantic Marine Mammal Commission ([[North Atlantic Marine Mammal Comission (NAMCO)|NAMMCO]]) and the [[Bern Convention]]. Fisheries regulations for the Celtic Sea are covered under national laws. The open waters of the North-east Atlantic are subject to international fisheries agreements: North East Atlantic Fisheries Commission ([[North East Atlantic Fisheries Commission (NEAFC)|NEAFC]]), North Atlantic Salmon Conservation Organization ([[North Atlantic Salmon Conservation Organisation (NASCO)|NASCO]]), and the International Convention for the Conservation of Atlantic Tunas ([[International Convention for the Conservation of Atlantic Tunas (ICCAT)|ICCAT]]). <br />
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To protect ecologically valuable areas, all countries have established some form of Marine Protected Areas ([[Marine Protected Area (MPA)|MPAs]]). Most of the MPAs are close to or adjacent to shores. However, many offshore areas are important spawning areas and nursery grounds that need protection, thus a considerable increase of offshore MPAs could be considered. <br />
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The discussed research projects and monitoring programmes in the North-east Atlantic Ocean are: the Continuous Plankton Recorder ([[Continuous Plankton Recorder (CPR)|CPR]]), [[BioMar]], Joint Assessment and Monitoring Programme ([[Joint Assessment and Monitoring Programme (JAMP)|JAMP]]), ICES fish stock monitoring and the Ocean Margin Exchange Programme ([[Ocean Margin Exchange Programme (OMEX)|OMEX]]). <br />
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[[Image:Lophelia.jpg|right|300px|''Lophelia pertusa'' Author: S. Ross ''et al.'', UNCW (www.safmc.net)|frame]]<br />
[[Image:distribution.jpg|center|300px|Cold-water reefs: ''Lophelia pertusa'' (red) and ''Madrepora oculata'' (green). Author:Uni Erlangen|frame]]<br />
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==The Arctic Ocean<ref name="The Arctic Ocean"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The Arctic Ocean''</ref>== <br />
[[Image:Arctic Ocean.jpg|right|300px|The Arctic Ocean<ref name="The Arctic Ocean"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The Arctic Ocean''</ref>|frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/arctic_ocean.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
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The Arctic Ocean covers a large area with harsh climatic conditions. The European part (surface area: 5 500 000 km²) of the Arctic Ocean covers only about 8 % of the total area of the Arctic Ocean, but due do its great depth it represents about 25 % of the total volume. The cold water penetrates southwards at great depths and contributes to the oxygenation of the world’s deep oceans. The formation of deep and intermediate waters in the European Arctic ocean is one of the most important features of the global oceanic circulation.<br />
The system of ocean currents induces an east-west temperature gradient with warmer conditions in the eastern part of the European Arctic Ocean, strongly influenced by the warm Gulf Stream. This keeps the Norwegian Sea and a large part of the Barents Sea ice-free and favorable for the growth of a wide range of open-sea (pelagic) and bottom-living (benthic) species. This biological production sustains huge stocks of pelagic fish in these areas.<br />
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The cold, the extreme variation in light conditions and the extensive ice cover in the area create unique marine ecosystems, and some species live on the border of their tolerance. Arctic marine food webs can be very complex, but with only a few key species connecting the different levels (OSPAR 2000). Bottom-dwelling communities can be very rich along the ice-free coasts, where kelp forests and seaweed become nursing grounds for many fish species (AMAP 1998).<br />
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As main traits to biodiversity in the Arctic Ocean are considered: [[Effects of global climate change on European marine biodiversity|climate changes]], [[Effects of fisheries on European marine biodiversity|fisheries]], offshore activities, shipping, contaminants, radioactive discharges and [[Effects of invasions on European marine biodiversity|introduced species]].<br />
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The three most important fish populations in the Barents Sea are herring, cod and capelin and these three species are biologically strongly linked: young herring feeds on capelin larvae, while young cod eats the mature capelin. Many seabirds (e.g. guillemots) are specialized top predators and are very sensible to changes in the lower trophic levels. Fisheries bycatch is the primary mortality factor for several seabird species. <br />
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Current and potential projects indicate that shipping probably will increase. The extreme climatic conditions heighten the risk of accidents and complicate rescue and clean-up work, thus increasing the risks of environmental damage. Oil films are frequently detected on the surface in areas of intense shipping. Other possible impacts of shipping are introduction of non-indigenous species and biological effects of antifoulants. There is a great potential for oil exploration in the Barents Sea and it is therefore likely that oil will pose a serious threat to marine life in the future.<br />
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Main political instruments discussed in the ‘EES-report’ are: the [[Arctic Council]] (the programme for the Conservation of Arctic Flora and Fauna ([[programme for the Conservation of Arctic Flora and Fauna (CAFF)|CAFF]]) and the Arctic Monitoring and Assessment Programme (AMAP) are two programmes under the Council), [[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], The North Atlantic Marine Mammal Commission ([[North Atlantic Marine Mammal Commission (NAMMCO)|NAMMCO]]) and the [[Bern convention]]. Further are there several national legal instruments for marine conservation in the Arctic, who are summarized by CAFF (2000b). (http://arcticportal.org/en/caff/). <br />
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The research projects and monitoring programmes are mainly carried out by AMAP and CAFF (developed a ‘Strategic plan for the conservation of Arctic biological diversity’ in 1998, and the plan identifies monitoring as one of the key objectives). There are also non-governmental organizations on the field, such as the International Arctic Science Committee and the Arctic Ocean Sciences Board.<br />
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==The Mediterranean Sea<ref name="The Mediterranean Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Mediterranean Sea''</ref>== <br />
[[Image:Mediterranean Sea.jpg|right|300px|The Mediterranean Sea<ref name="The Mediterranean Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Mediterranean Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/MediterSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
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The Mediterranean Sea (surface area: 2.5 million km²) is the largest semi-enclosed European sea. The sea is oligotrophic: it is rich in oxygen and poor in nutrients. Oligotrophy increases from west to east. <br />
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The legal framework for the conservation of natural habitats and species in the Mediterranean is provided by on the one hand, conventions validly for the whole Mediterranean Sea and on the other hand conventions which are only valid for the European Member States along the northern shore of the sea (e.g. Convention through the protection of coastal and marine habitats and species, provided by the EU Birds and Habitats Directives).<br />
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The fauna and flora is one of the species richest of the world and there is a high rate of endemism. Compared with the Atlantic, the Mediterranean marine communities have many different species with generally smaller individuals (Mediterranean nanism) having a shorter life cycle. The oligotrophic water results in low primary production rates, combined with poor development of higher levels of the food chain, including low fish production.<br />
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[[Eutrophication|Eutrophication]], microbial contamination, [[Effects of fisheries on European marine biodiversity|fishing]], exploitation of living resources and mariculture, industrial and oil pollution and the [[Effects of invasions on European marine biodiversity|establishment of alien species]] are considered as main threats to biodiversity in the Mediterranean Sea. <br />
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Eutrophication in coastal areas has almost certainly resulted in an increase in fish catches of some pelagic fish species in the formerly low-nutrient waters of the Mediterranean Sea<br />
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Introduction of alien species through ballast waters, fouling, import and invasion has resulted in the establishment of dense populations of invading species. The impact of some intruders, such as the tropical alga ''Caulerpa taxifolia'' has had catastrophic effects on the natural environment.<br />
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Fishing has resulted in overexploitation of several fish stocks in the Mediterranean. Mortality of the monk seal (''Monachus schauinslandi'') is mostly associated with fishing. Over exploitation by intensive collection has led to a serious decline in some corals and many shellfish.<br />
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The EEA report reproduces a list of conventions, directives and action plans for nature protection in the Mediterranean Sea. <br />
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There are 47 [[Specialy Protected Area|SPA]] (Specially Protected Area) sites witch cover marine Mediterranean areas under the UNEP Protocol. But among the signatories of the protocol, only Italy has specific legislation for the establishment of marine protected areas.<br />
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The research and monitoring programmes are focused on pollution assessment. Presently no monitoring of plankton, benthos or fish is undertaken at the Mediterranean scale and the Mediterranean cetology is still in its infancy.<br />
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==The Black Sea<ref name="The Black Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Black Sea''</ref>== <br />
[[Image:Black Sea.jpg|right|300px|The Black Sea<ref name="The Black Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Black Sea''</ref> |frame]] <br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/BlackSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
Nearly 87 % of the Black Sea (surface area: 423 000 km²) is entirely anoxic (without oxygen) and contains high levels of hydrogen sulphide. This is the result of past geological events, its shape and its specific water balance (high degree of isolation from the world ocean, deep water depression in the centre of the sea, the extensive drainage basin and the large number of incoming rivers). <br />
<br />
Due to anoxia in large parts of deeper waters, deep pelagic and benthic organisms are largely absent. The structure of marine ecosystems differs from the neighboring Mediterranean Sea by a lower species variety (ratio of the Mediterranean to Black Sea for species richness is three) and the dominant groups are different. However the total biomass and productivity of the Black Sea is much higher.<br />
<br />
The considered main threats to biodiversity in the Black Sea are [[Eutrophication|eutrophication]], contamination and oil pollution, water management and regulation, [[Effects of fisheries on European marine biodiversity|fisheries]] and [[Effects of invasions on European marine biodiversity|alien species]].<br />
<br />
The wide diversity of biotopes provides favorable conditions for invasions of alien species to the Black Sea. The composition and structure of the marine communities is constantly changing with the decline of certain species and the expansion of others.<br />
<br />
Increasing salinity due to inappropriate water management and regulation, and pollution of brackish coastal lakes and estuaries represents a threat to relics and [[Endemic|endemic]] species, especially in the Sea of Azov.<br />
<br />
Deterioration of some marine habitats and a lack of laws and technology for regulating the introduction of alien species, for example via ballast waters, have allowed the invasion of such species. A prominent example of an alien species is that of the comb jellyfish ''Mnemiopsis leidyi''. These have produced mass populations, what have changed the equilibrium of the native marine ecosystems. <br />
<br />
The Convention on Biological Diversity has been signed and ratified by all Black Sea countries, however there is no univocal legislation for the specific conventions, validly for all Black Sea countries. For example, no overall management of fish stocks in the Black sea is in place (the convention on Fishing in the Black Sea has not been signed by Turkey). [[International Convention for the Prevention of Pollution From Ships (MARPOL)|MARPOL]] (Prevention of Marine Pollution from ships) have already come into force but are only slowly being implemented.<br />
There are more than 20 nature reserves in the Black Sea, but many reserves still lack effective management plans and infrastructure.<br />
<br />
The Black Sea Environmental Programme ([[Black Sea Environmental Programme (BSEP)|BSEP]]) is set up in 1993, to provide a sustainable basis for managing the Black Sea. The most important realizations of the BSEP are the Trans boundary Diagnostic Analysis of the Black Sea (GEF-BSEP/UN, 1997) and the publications of the Black Sea Red Data Book (GEF-BSEP/UN, 1999). <br />
<br />
[[Image:combjellyfish.jpg|center|300px|comb jellyfish ''Mnemiopsis leidyi'' SOURCE:www.livt.net |frame]]<br />
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<br />
==The Caspian Sea<ref name="The Caspian Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Caspian Sea''</ref>== <br />
[[Image:Caspian Sea.jpg|right|300px|The Caspian sea<ref name="The Caspian Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Caspian Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/CaspianSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
The Caspian Sea is the largest (surface area: 390 000 km²) enclosed sea in the world. It is brackish, with salinity up to 13.7 ‰. The typical brackish-water fauna formed as from the Mid-Pliocene, when the Caspian Sea was completely isolated from the Black Sea.<br />
<br />
One of the most important features of the Caspian Sea is its changing water level, which has a significant effect on biodiversity in the extensive shallow areas. The factors causing these fluctuations are not well understood and causes are hotly debated. <br />
<br />
The high biological diversity of the Caspian Sea makes the region one of the most valuable ecosystems. Many species are endemic and there are many representatives from almost all major groups on earth. The most important fauna of the Caspian Sea is the sturgeon, which constitute 85 % of the standing stock of the world’s sturgeon population. The Caspian Sea lies on the crossing of migration routes of millions of migrating birds and offers refuge for a number of rare and endangered birds.<br />
<br />
The considered main threats to biodiversity in the Caspian Sea and its coastal zone are combinations of natural and anthropogenic factors including pollution, sea level fluctuation, river regulation, poaching over [[Effects of fisheries on European marine biodiversity|overfishing]] and [[Effects of invasions on European marine biodiversity|introduction of alien species]]. <br />
<br />
Regulation of the Caspian rivers, causing reduction in the area of delta vegetation, loss of reeds, cattail and bushes. Loss of vegetation results in loss of aquatic and coastal fauna. Many anadromous and semi-migratory species have been deprived of their natural spawning grounds.<br />
<br />
Most of the threats to the biodiversity of the Caspian are trans boundary in nature and require effective measures from all Caspian states, for this reason is the Caspian Environment Programme ([[Caspian Environment Programme (CEP)|CEP]], 1998) launched by the riparian states.<br />
<br />
Since the collapse of the Soviet Union, the legal framework for the fishery changed and this created a difficult situation for the management of the sturgeon resources. <br />
<br />
There has been little study on the biodiversity of the Caspian Sea. There is an urgent need to undertake an ecological survey of the coastal and marine species and habitats, their uses, values and threats, for each of the five Caspian states, which will result in an inventory of Caspian ecological resources. Strategies for the management of trans boundary biodiversity, including threatened or endangered migratory species need to be developed.<br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Biodiversity_in_the_European_Seas&diff=11621Biodiversity in the European Seas2007-09-03T09:04:50Z<p>Ltherry: /* The Baltic Sea<ref name="Baltic Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref> */</p>
<hr />
<div>This article acts about the [[Biodiversity_in_the_valuation_concept|biodiversity]] in the European Seas. We refer to [http://reports.eea.europa.eu/report_2002_0524_154909/en reports (publish date: 31 may 2002) of the ‘European Environmental Agency’ (visited 31/08/2007)]([[European Environmental Agency (EEA)|EEA]]), in which each Sea is treated closely with a large attention for the marine biodiversity. In the ‘EEA reports’ an overview is given of the most important physical, biological and exploitation characteristics, the main threats to biodiversity and the policies at work (nature protection and protection of marine resources by restrictions on fishing and hunting).The contents of these reports are reflected with the indication of the most relevant information.<br />
<br />
==The North Sea<ref name="North Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The North Sea''</ref>== <br />
<br />
[[Image:North Sea.jpg|right|300px|North Sea<ref name="North Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/NorthSea.pdf''link to actual EEA report'' (visited: 31/08/2007)]<br />
<br />
The North Sea is a shallow sea (average depth: 90 m) with a surface area of 750 000 km². It is rather a young ecosystem formed by the flooding of a landmass some 20 000 years ago. Its coast and waters are still being colonized by new species from the Atlantic. <br />
<br />
As main influences on the North Seas ecosystem are considered: [[Effects of fisheries on European marine biodiversity|fisheries]], [[Eutrophication|eutrophication]], offshore industry, maritime traffic, industry and tourism. <br />
<br />
The strong coupling between [[benthic]] and [[pelagic]] communities in the shallow parts of the sea makes it extremely productive and one of the most productive areas in the world, with a wide range of [[plankton]], fish, seabirds and benthic communities. The North Sea is one of the world’s most important fishing grounds. The sea is also rich in oil and gas. Many human activities have an impact on the biodiversity of the North Sea. The marine ecosystems are under intense pressure from fishing, fish farming, kelp harvesting, invading species, nutrient input, recreational use, habitat loss and [[Effects of global climate change on European marine biodiversity|climate changes]]; most notable are the effects of fisheries and eutrophication.<br />
<br />
The policy conducted in the North Sea has several objectives, from nature protection (discussed conventions/agreements are [[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], [[International Council for the Exploration of the Sea (ICES)|ICES]], [[Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS)|ASCOBANS]] and the [[North_Sea_pollution_from_shipping:_legal_framework#The_Bonn_Agreement|Bonn Convention]], [[Trilateral Wadden Sea Cooperation]], [[North Sea Conference]], [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]] and [[Bern Convention]]) to protection of marine resources (ASCOBANS, the EU Common Fisheries Policy ([[EU Comon Fisheries Policy (CFP)|CFP]])). <br />
<br />
Furthermore, there are several national, international and non-governmental organization initiatives to assess environmental quality in the North Sea area. The most important are: the ‘continuous plankton recorder’ ([[Continuous Plankton Recorder (CPR)|CPR]]), [[BioMar]] an the ‘Joint assessment and monitoring programme’ ([[Joint Assessment and Monitoring Programme (JAMP)|JAMP]]). <br />
<br />
<br />
<br />
[[Image:CPR.jpg|center|300px|Diagram showing a cutaway view of the `'''Continuous Plankton Recorder'''`(CPR) , the plankton filtering mechanism, and a photograph of the instrument. SOURCE: www.sahfos.ac.uk|frame]]<br />
<br />
<br />
==The Baltic Sea<ref name="Baltic Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref>== <br />
[[Image:Baltic Sea.jpg|right|300px|The Baltic Sea<ref name="Baltic Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - Seas around Europe - The Baltic Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/BalticSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
The Baltic Sea is the largest (surface area: 370 000 km²) brackish water system in the world. The shallow sounds between Sweden and Denmark provide a limited water exchange with the North Sea. It takes 25-35 years for all the water in the Baltic to be replenished by water from the North Sea and beyond.<br />
<br />
The Baltic Sea has marked [[stratification]] between low-salinity surface water and the more saline deep water at a depth of about 40-70 m. This salinity barrier prevents the exchange of oxygen and nutrients, and large parts of the seabed are lifeless because of oxygen depletion. The vertical and horizontal salinity gradients are reflected in different species communities and species numbers. The highest biodiversity is found in the south-west of the Baltic Sea.<br />
<br />
The Baltic Sea is slowly shrinking because of geological uplifting of land after the last glaciation.<br />
<br />
Because of the geologically short time aspect (the Baltic Sea is formed after the last glaciation as the ice retreated some 10 000 years ago) and major changes, a very limited brackish water flora and fauna has developed. The Baltic Sea is therefore characterized by few species, but many individuals of each species.<br />
<br />
The considered main threats to biodiversity are [[Eutrophication|eutrophication]], [[Effects of fisheries on European marine biodiversity|fisheries]], pollution of oil and contaminants, constructions and [[Effects of invasions on European marine biodiversity|introduction of non-indigenous species]]. <br />
<br />
Nearly enclosed seas such as the Baltic are particularly sensitive to inputs of pollutants, because of the long residence time of the water (25 to 35 years). Although concentrations of most of the hazardous substances have decreased over the past 30 years in the Baltic area, a number of them are still of environmental concern, such as cadmium, dioxins and PCBs. One of the effects of contamination is sterility in a large part of the Baltic mammals population (probably due to PCB poisoning). <br />
<br />
The discussed political instruments of application on the Baltic Sea are the Helsinki Convention of 1974 ([[The Helsinki Commission (HELCOM)|HELCOM]]), the International Baltic Sea Fishery Commission ([[International Baltic Sea Fishery Commission (IBSFC)|IBSFC]]), [[Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS)|ASCOBANS]], the [[Ramsar Convention]], [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]], the [[Bern Convention]] and [[Bird_Directive%2C_Habitat_Directive%2C_NATURA_2000#NATURA_2000|Natura 2000]].<br />
<br />
The [[Baltic Monitoring Programme]], as part of COMBINE (Co-operative Monitoring in the Baltic Marine Environment), is implemented by the Helsinki Commission. The aims are to identify and quantify the effects of anthropogenic discharges/activities in the Baltic Sea in the context of the natural variations in the system, and to identify and quantify the changes in the environment as a result of regulatory actions.<br />
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==The North-east Atlantic Ocean<ref name="NE Atlantic"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The North-east Atlantic Ocean''</ref>== <br />
[[Image:NE Atlantic.jpg|right|300px|The North-east Atlantic Ocean<ref name="NE Atlantic"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The North-east Atlantic Ocean''</ref>|frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/nea_ocean.pdf''link to actual EEA report'' (visited 31/08/2007) ]<br />
<br />
The North-east Atlantic Ocean is a part of the Atlantic Ocean. The morphology of the sea floor is dominated by two deep areas on both sides of the Mid Atlantic Ridge with depths down to 5 000 m and a shallow continental shelf along the European coast.<br />
<br />
The formation of the North Atlantic deep water is one of the driving forces for the thermohaline circulation of the world’s oceans. The water flow is predominantly from west to east.<br />
<br />
The primary productivity in the open ocean is low, but is increasing from south to north and towards shore. Cold-water reefs with ''Lophelia pertusa'' as the main reef building species are present along the coasts of the whole area. In deep water outside Scotland and Ireland there are large areas covered by cold water corals formed by two species, ''Lophelia pertusa'' and ''Madrepora oculata'', which interconnect with tubes of the worm ''Eunice norvegicus''. These deep-water reefs have a high biodiversity. <br />
<br />
As main threats to biodiversity in the North-east Atlantic Ocean are considered: [[Effects of global climate change on European marine biodiversity|climatic changes]], [[Effects of fisheries on European marine biodiversity|fisheries]], mariculture, [[Effects of invasions on European marine biodiversity|introduced species]], [[Eutrophication|eutrophication]] and pollution of oil and contaminants. The biodiversity is high, but several species in the area are endangered of which lack of sustainable fishery management is probably the most important threat. Eutrophication is not regarded as a problem for this sea except for some local coastal areas, mainly estuaries in the Celtic sea and some estuaries along the coast of Biscay.<br />
<br />
[[International Council for the Exploration of the Sea (ICES)|ICES]](1996) indicates that there is a need for a 40 % reduction in the fishing fleet to avoid over-fishing and match available fish resources. Most of the commercial fish stocks are outside ‘safe biological limit’ in the Atlantic area (OSPAR, 2000; EEA, 2002) including cod, hake, saithe, plaice, sole, sardine, anglerfish and megrims. <br />
<br />
Several legal instruments aim to protect and conserve the marine life in the North-east Atlantic Ocean: ([[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], ICES, [[Bird Directive, Habitat Directive, NATURA 2000|EU Birds and Habitats Directives]], North Atlantic Marine Mammal Commission ([[North Atlantic Marine Mammal Comission (NAMCO)|NAMMCO]]) and the [[Bern Convention]]. Fisheries regulations for the Celtic Sea are covered under national laws. The open waters of the North-east Atlantic are subject to international fisheries agreements: North East Atlantic Fisheries Commission ([[North East Atlantic Fisheries Commission (NEAFC)|NEAFC]]), North Atlantic Salmon Conservation Organization ([[North Atlantic Salmon Conservation Organisation (NASCO)|NASCO]]), and the International Convention for the Conservation of Atlantic Tunas ([[International Convention for the Conservation of Atlantic Tunas (ICCAT)|ICCAT]]). <br />
<br />
To protect ecologically valuable areas, all countries have established some form of Marine Protected Areas ([[Marine Protected Area (MPA)|MPAs]]). Most of the MPAs are close to or adjacent to shores. However, many offshore areas are important spawning areas and nursery grounds that need protection, thus a considerable increase of offshore MPAs could be considered. <br />
<br />
The discussed research projects and monitoring programmes in the North-east Atlantic Ocean are: the Continuous Plankton Recorder ([[Continuous Plankton Recorder (CPR)|CPR]]), [[BioMar]], Joint Assessment and Monitoring Programme ([[Joint Assessment and Monitoring Programme (JAMP)|JAMP]]), ICES fish stock monitoring and the Ocean Margin Exchange Programme ([[Ocean Margin Exchange Programme (OMEX)|OMEX]]). <br />
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[[Image:Lophelia.jpg|right|300px|''Lophelia pertusa'' Author: S. Ross ''et al.'', UNCW (www.safmc.net)|frame]]<br />
[[Image:distribution.jpg|center|300px|Cold-water reefs: ''Lophelia pertusa'' (red) and ''Madrepora oculata'' (green). Author:Uni Erlangen|frame]]<br />
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==The Arctic Ocean<ref name="The Arctic Ocean"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The Arctic Ocean''</ref>== <br />
[[Image:Arctic Ocean.jpg|right|300px|The Arctic Ocean<ref name="The Arctic Ocean"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - The Arctic Ocean''</ref>|frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/arctic_ocean.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
The Arctic Ocean covers a large area with harsh climatic conditions. The European part (surface area: 5 500 000 km²) of the Arctic Ocean covers only about 8 % of the total area of the Arctic Ocean, but due do its great depth it represents about 25 % of the total volume. The cold water penetrates southwards at great depths and contributes to the oxygenation of the world’s deep oceans. The formation of deep and intermediate waters in the European Arctic ocean is one of the most important features of the global oceanic circulation.<br />
The system of ocean currents induces an east-west temperature gradient with warmer conditions in the eastern part of the European Arctic Ocean, strongly influenced by the warm Gulf Stream. This keeps the Norwegian Sea and a large part of the Barents Sea ice-free and favorable for the growth of a wide range of open-sea (pelagic) and bottom-living (benthic) species. This biological production sustains huge stocks of pelagic fish in these areas.<br />
<br />
The cold, the extreme variation in light conditions and the extensive ice cover in the area create unique marine ecosystems, and some species live on the border of their tolerance. Arctic marine food webs can be very complex, but with only a few key species connecting the different levels (OSPAR 2000). Bottom-dwelling communities can be very rich along the ice-free coasts, where kelp forests and seaweed become nursing grounds for many fish species (AMAP 1998).<br />
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As main traits to biodiversity in the Arctic Ocean are considered: [[Effects of global climate change on European marine biodiversity|climate changes]], [[Effects of fisheries on European marine biodiversity|fisheries]], offshore activities, shipping, contaminants, radioactive discharges and [[Effects of invasions on European marine biodiversity|introduced species]].<br />
<br />
The three most important fish populations in the Barents Sea are herring, cod and capelin and these three species are biologically strongly linked: young herring feeds on capelin larvae, while young cod eats the mature capelin. Many seabirds (e.g. guillemots) are specialized top predators and are very sensible to changes in the lower trophic levels. Fisheries bycatch is the primary mortality factor for several seabird species. <br />
<br />
Current and potential projects indicate that shipping probably will increase. The extreme climatic conditions heighten the risk of accidents and complicate rescue and clean-up work, thus increasing the risks of environmental damage. Oil films are frequently detected on the surface in areas of intense shipping. Other possible impacts of shipping are introduction of non-indigenous species and biological effects of antifoulants. There is a great potential for oil exploration in the Barents Sea and it is therefore likely that oil will pose a serious threat to marine life in the future.<br />
<br />
Main political instruments discussed in the ‘EES-report’ are: the [[Arctic Council]] (the programme for the Conservation of Arctic Flora and Fauna ([[programme for the Conservation of Arctic Flora and Fauna (CAFF)|CAFF]]) and the Arctic Monitoring and Assessment Programme (AMAP) are two programmes under the Council), [[Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)|OSPAR]], The North Atlantic Marine Mammal Commission ([[North Atlantic Marine Mammal Commission (NAMMCO)|NAMMCO]]) and the [[Bern convention]]. Further are there several national legal instruments for marine conservation in the Arctic, who are summarized by CAFF (2000b). (http://arcticportal.org/en/caff/). <br />
<br />
The research projects and monitoring programmes are mainly carried out by AMAP and CAFF (developed a ‘Strategic plan for the conservation of Arctic biological diversity’ in 1998, and the plan identifies monitoring as one of the key objectives). There are also non-governmental organizations on the field, such as the International Arctic Science Committee and the Arctic Ocean Sciences Board.<br />
<br />
<br />
==The Mediterranean Sea<ref name="The Mediterranean Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Mediterranean Sea''</ref>== <br />
[[Image:Mediterranean Sea.jpg|right|300px|The Mediterranean Sea<ref name="The Mediterranean Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Mediterranean Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/MediterSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
The Mediterranean Sea (surface area: 2.5 million km²) is the largest semi-enclosed European sea. The sea is oligotrophic: it is rich in oxygen and poor in nutrients. Oligotrophy increases from west to east. <br />
<br />
The legal framework for the conservation of natural habitats and species in the Mediterranean is provided by on the one hand, conventions validly for the whole Mediterranean Sea and on the other hand conventions which are only valid for the European Member States along the northern shore of the sea (e.g. Convention through the protection of coastal and marine habitats and species, provided by the EU Birds and Habitats Directives).<br />
<br />
The fauna and flora is one of the species richest of the world and there is a high rate of endemism. Compared with the Atlantic, the Mediterranean marine communities have many different species with generally smaller individuals (Mediterranean nanism) having a shorter life cycle. The oligotrophic water results in low primary production rates, combined with poor development of higher levels of the food chain, including low fish production.<br />
<br />
[[Eutrophication|Eutrophication]], microbial contamination, [[Effects of fisheries on European marine biodiversity|fishing]], exploitation of living resources and mariculture, industrial and oil pollution and the [[Effects of invasions on European marine biodiversity|establishment of alien species]] are considered as main threats to biodiversity in the Mediterranean Sea. <br />
<br />
Eutrophication in coastal areas has almost certainly resulted in an increase in fish catches of some pelagic fish species in the formerly low-nutrient waters of the Mediterranean Sea<br />
<br />
Introduction of alien species through ballast waters, fouling, import and invasion has resulted in the establishment of dense populations of invading species. The impact of some intruders, such as the tropical alga ''Caulerpa taxifolia'' has had catastrophic effects on the natural environment.<br />
<br />
Fishing has resulted in overexploitation of several fish stocks in the Mediterranean. Mortality of the monk seal (''Monachus schauinslandi'') is mostly associated with fishing. Over exploitation by intensive collection has led to a serious decline in some corals and many shellfish.<br />
<br />
The EEA report reproduces a list of conventions, directives and action plans for nature protection in the Mediterranean Sea. <br />
<br />
There are 47 [[Specialy Protected Area|SPA]] (Specially Protected Area) sites witch cover marine Mediterranean areas under the UNEP Protocol. But among the signatories of the protocol, only Italy has specific legislation for the establishment of marine protected areas.<br />
<br />
The research and monitoring programmes are focused on pollution assessment. Presently no monitoring of plankton, benthos or fish is undertaken at the Mediterranean scale and the Mediterranean cetology is still in its infancy.<br />
<br />
==The Black Sea<ref name="The Black Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Black Sea''</ref>== <br />
[[Image:Black Sea.jpg|right|300px|The Black Sea<ref name="The Black Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Black Sea''</ref> |frame]] <br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/BlackSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
Nearly 87 % of the Black Sea (surface area: 423 000 km²) is entirely anoxic (without oxygen) and contains high levels of hydrogen sulphide. This is the result of past geological events, its shape and its specific water balance (high degree of isolation from the world ocean, deep water depression in the centre of the sea, the extensive drainage basin and the large number of incoming rivers). <br />
<br />
Due to anoxia in large parts of deeper waters, deep pelagic and benthic organisms are largely absent. The structure of marine ecosystems differs from the neighboring Mediterranean Sea by a lower species variety (ratio of the Mediterranean to Black Sea for species richness is three) and the dominant groups are different. However the total biomass and productivity of the Black Sea is much higher.<br />
<br />
The considered main threats to biodiversity in the Black Sea are [[Eutrophication|eutrophication]], contamination and oil pollution, water management and regulation, [[Effects of fisheries on European marine biodiversity|fisheries]] and [[Effects of invasions on European marine biodiversity|alien species]].<br />
<br />
The wide diversity of biotopes provides favorable conditions for invasions of alien species to the Black Sea. The composition and structure of the marine communities is constantly changing with the decline of certain species and the expansion of others.<br />
<br />
Increasing salinity due to inappropriate water management and regulation, and pollution of brackish coastal lakes and estuaries represents a threat to relics and [[Endemic|endemic]] species, especially in the Sea of Azov.<br />
<br />
Deterioration of some marine habitats and a lack of laws and technology for regulating the introduction of alien species, for example via ballast waters, have allowed the invasion of such species. A prominent example of an alien species is that of the comb jellyfish ''Mnemiopsis leidyi''. These have produced mass populations, what have changed the equilibrium of the native marine ecosystems. <br />
<br />
The Convention on Biological Diversity has been signed and ratified by all Black Sea countries, however there is no univocal legislation for the specific conventions, validly for all Black Sea countries. For example, no overall management of fish stocks in the Black sea is in place (the convention on Fishing in the Black Sea has not been signed by Turkey). [[International Convention for the Prevention of Pollution From Ships (MARPOL)|MARPOL]] (Prevention of Marine Pollution from ships) have already come into force but are only slowly being implemented.<br />
There are more than 20 nature reserves in the Black Sea, but many reserves still lack effective management plans and infrastructure.<br />
<br />
The Black Sea Environmental Programme ([[Black Sea Environmental Programme (BSEP)|BSEP]]) is set up in 1993, to provide a sustainable basis for managing the Black Sea. The most important realizations of the BSEP are the Trans boundary Diagnostic Analysis of the Black Sea (GEF-BSEP/UN, 1997) and the publications of the Black Sea Red Data Book (GEF-BSEP/UN, 1999). <br />
<br />
[[Image:combjellyfish.jpg|center|300px|comb jellyfish ''Mnemiopsis leidyi'' SOURCE:www.livt.net |frame]]<br />
<br />
<br />
==The Caspian Sea<ref name="The Caspian Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Caspian Sea''</ref>== <br />
[[Image:Caspian Sea.jpg|right|300px|The Caspian sea<ref name="The Caspian Sea"> EEA (2002). ''Europe`s biodiversity - biogeographical regions and seas - seas around Europe - The Caspian Sea''</ref> |frame]]<br />
[http://reports.eea.europa.eu/report_2002_0524_154909/en/CaspianSea.pdf''link to actual EEA report'' (visited 31/08/2007)]<br />
<br />
The Caspian Sea is the largest (surface area: 390 000 km²) enclosed sea in the world. It is brackish, with salinity up to 13.7 ‰. The typical brackish-water fauna formed as from the Mid-Pliocene, when the Caspian Sea was completely isolated from the Black Sea.<br />
<br />
One of the most important features of the Caspian Sea is its changing water level, which has a significant effect on biodiversity in the extensive shallow areas. The factors causing these fluctuations are not well understood and causes are hotly debated. <br />
<br />
The high biological diversity of the Caspian Sea makes the region one of the most valuable ecosystems. Many species are endemic and there are many representatives from almost all major groups on earth. The most important fauna of the Caspian Sea is the sturgeon, which constitute 85 % of the standing stock of the world’s sturgeon population. The Caspian Sea lies on the crossing of migration routes of millions of migrating birds and offers refuge for a number of rare and endangered birds.<br />
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The considered main threats to biodiversity in the Caspian Sea and its coastal zone are combinations of natural and anthropogenic factors including pollution, sea level fluctuation, river regulation, poaching over [[Effects of fisheries on European marine biodiversity|overfishing] and [[Effects of invasions on European marine biodiversity|introduction of alien species]]. <br />
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Regulation of the Caspian rivers, causing reduction in the area of delta vegetation, loss of reeds, cattail and bushes. Loss of vegetation results in loss of aquatic and coastal fauna. Many anadromous and semi-migratory species have been deprived of their natural spawning grounds.<br />
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Most of the threats to the biodiversity of the Caspian are trans boundary in nature and require effective measures from all Caspian states, for this reason is the Caspian Environment Programme ([[Caspian Environment Programme (CEP)|CEP]], 1998) launched by the riparian states.<br />
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Since the collapse of the Soviet Union, the legal framework for the fishery changed and this created a difficult situation for the management of the sturgeon resources. <br />
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There has been little study on the biodiversity of the Caspian Sea. There is an urgent need to undertake an ecological survey of the coastal and marine species and habitats, their uses, values and threats, for each of the five Caspian states, which will result in an inventory of Caspian ecological resources. Strategies for the management of trans boundary biodiversity, including threatened or endangered migratory species need to be developed.<br />
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==References==<br />
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{{author<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11619Effects of fisheries on European marine biodiversity2007-09-02T13:35:40Z<p>Ltherry: </p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
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When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Trophic cascading effect=== <br />
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Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
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===‘Food-web’ competition=== <br />
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[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
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Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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{{author<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Trophic_level_-_a_marine_example&diff=11618Trophic level - a marine example2007-09-02T13:27:03Z<p>Ltherry: </p>
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<div>{{<br />
Definition|title=Trophic level<br />
|definition=Throphic levels are the layers that make up [[Food web|food webs]], wherein animals are ranked according to how many steps they are above the primary producers at the base of the food web. Microscopic plants at the bottom are assigned a throphic level of 1, while the herbivores and detritivors that feed on the plants and detritus make up trophic level 2. Higher order carnivores such as most marine mammals, are assigned trophic levels ranging from 3 to 5. Animals that feed from more than one trophic level have non-integer trophic levels. Thus knowing what an animal eats is all that is needed to calculate its trophic level.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> }}<br />
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[[Image:trophic level.jpg|center|300px|Trophic levels were initially defined to include only discrete steps (left). Organic detritus and microscopic plants (phytoplankton) occupy the first trophic level. Tiny zooplankton, which feed on phytoplankton, reside at the second level. Creatures that eat zooplankton sit at the third level, and so forth. But many marine creatures feed from multiple trophic levels and so could not be fit into this classic scheme. Thus the modern approach allows the assignment of trophic level to span a continuum rather than forcing it to take on integral values. Marine biologists would, for example, assign the anchovy (''Engraulis encrasicolus'') which supplements its main diet of phytoplankton with some zooplankton, to a trophic level of about 2.2; people fishing for anchovies (and eating a diet of only these small fish) would then be assigned a trophic level of 3.2 (right). Author:Edward Roberts SOURCE: www.seafriends.org|frame]]<br />
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==References==<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Trophic_level_-_a_marine_example&diff=11617Trophic level - a marine example2007-09-02T13:22:36Z<p>Ltherry: </p>
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<div>{{<br />
Definition|title=Trophic level<br />
|definition=Throphic levels are the layers that make up food webs, wherein animals are ranked according to how many steps they are above the primary producers at the base of the food web. Microscopic plants at the bottom are assigned a throphic level of 1, while the herbivores and detritivors that feed on the plants and detritus make up trophic level 2. Higher order carnivores such as most marine mammals, are assigned trophic levels ranging from 3 to 5. Animals that feed from more than one trophic level have non-integer trophic levels. Thus knowing what an animal eats is all that is needed to calculate its trophic level.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> }}<br />
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[[Image:trophic level.jpg|center|300px|Trophic levels were initially defined to include only discrete steps (left). Organic detritus and microscopic plants (phytoplankton) occupy the first trophic level. Tiny zooplankton, which feed on phytoplankton, reside at the second level. Creatures that eat zooplankton sit at the third level, and so forth. But many marine creatures feed from multiple trophic levels and so could not be fit into this classic scheme. Thus the modern approach allows the assignment of trophic level to span a continuum rather than forcing it to take on integral values. Marine biologists would, for example, assign the anchovy (''Engraulis encrasicolus'') which supplements its main diet of phytoplankton with some zooplankton, to a trophic level of about 2.2; people fishing for anchovies (and eating a diet of only these small fish) would then be assigned a trophic level of 3.2 (right). Author:Edward Roberts SOURCE: www.seafriends.org|frame]]<br />
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==References==<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Trophic_level_-_a_marine_example&diff=11616Trophic level - a marine example2007-09-02T13:14:58Z<p>Ltherry: </p>
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<div>Throphic levels are the layers that make up food webs, wherein animals are ranked according to how many steps they are above the primary producers at the base of the food web. Microscopic plants at the bottom are assigned a throphic level of 1, while the herbivores and detritivors that feed on the plants and detritus make up trophic level 2. Higher order carnivores such as most marine mammals, are assigned trophic levels ranging from 3 to 5. Animals that feed from more than one trophic level have non-integer trophic levels. Thus knowing what an animal eats is all that is needed to calculate its trophic level.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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[[Image:trophic level.jpg|center|300px|Trophic levels were initially defined to include only discrete steps (left). Organic detritus and microscopic plants (phytoplankton) occupy the first trophic level. Tiny zooplankton, which feed on phytoplankton, reside at the second level. Creatures that eat zooplankton sit at the third level, and so forth. But many marine creatures feed from multiple trophic levels and so could not be fit into this classic scheme. Thus the modern approach allows the assignment of trophic level to span a continuum rather than forcing it to take on integral values. Marine biologists would, for example, assign the anchovy (''Engraulis encrasicolus'')which supplements its main diet of phytoplankton with some zooplankton, to a trophic level of about 2.2; people fishing for anchovies (and eating a diet of only these small fish) would then be assigned a trophic level of 3.2 (right). Author:Edward Roberts SOURCE: www.seafriends.org|frame]]<br />
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==References==<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Trophic_level_-_a_marine_example&diff=11615Trophic level - a marine example2007-09-02T13:07:51Z<p>Ltherry: </p>
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<div>Throphic levels are the layers that make up food webs, wherein animals are ranked according to how many steps they are above the primary producers at the base of the food web. Microscopic plants at the bottom are assigned a throphic level of 1, while the herbivores and detritivors that feed on the plants and detritus make up trophic level 2. Higher order carnivores such as most marine mammals, are assigned trophic levels ranging from 3 to 5. Animals that feed from more than ane trophic level have non-integer trophic levels. Thus knowing what an animal eats is all that is needed to calculate its trophic level.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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[[Image:trophic level.jpg|center|300px|Trophic levels were initially defined to include only discrete steps (left). Organic detritus and microscopic plants (phytoplankton) occupy the first trophic level. Tiny zooplankton, which feed on phytoplankton, reside at the second level. Creatures that eat zooplankton sit at the third level, and so forth. But many marine creatures feed from multiple trophic levels and so could not be fit into this classic scheme. Thus the modern approach allows the assignment of trophic level to span a continuum rather than forcing it to take on integral values. Marine biologists would, for example, assign the anchovy, which supplements its main diet of phytoplankton with some zooplankton, to a trophic level of about 2.2; people fishing for anchovies (and eating a diet of only these small fish) would then be assigned a trophic level of 3.2 (right). Author:Edward Roberts SOURCE: www.seafriends.org|frame]]<br />
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==References==<br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=File:Trophic_level.jpg&diff=11614File:Trophic level.jpg2007-09-02T13:06:23Z<p>Ltherry: </p>
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<div></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Trophic_level_-_a_marine_example&diff=11613Trophic level - a marine example2007-09-02T13:06:01Z<p>Ltherry: </p>
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<div>Throphic levels are the layers that make up food webs, wherein animals are ranked according to how many steps they are above the primary producers at the base of the food web. Microscopic plants at the bottom are assigned a throphic level of 1, while the herbivores and detritivors that feed on the plants and detritus make up trophic level 2. Higher order carnivores such as most marine mammals, are assigned trophic levels ranging from 3 to 5. Animals that feed from more than ane trophic level have non-integer trophic levels. Thus knowing what an animal eats is all that is needed to calculate its trophic level.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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[[Image:trophic level.jpg|center|300px|Trophic levels were initially defined to include only discrete steps (left). Organic detritus and microscopic plants (phytoplankton) occupy the first trophic level. Tiny zooplankton, which feed on phytoplankton, reside at the second level. Creatures that eat zooplankton sit at the third level, and so forth. But many marine creatures feed from multiple trophic levels and so could not be fit into this classic scheme. Thus the modern approach allows the assignment of trophic level to span a continuum rather than forcing it to take on integral values. Marine biologists would, for example, assign the anchovy, which supplements its main diet of phytoplankton with some zooplankton, to a trophic level of about 2.2; people fishing for anchovies (and eating a diet of only these small fish) would then be assigned a trophic level of 3.2 (right). Author:Edward Roberts SOURCE: www.seafriends.org|frame]]<br />
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<references/><br />
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[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11612Effects of fisheries on European marine biodiversity2007-09-02T12:49:46Z<p>Ltherry: </p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean [[Trophic level|trophic level]] of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean trophic level of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
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When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Trophic cascading effect=== <br />
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Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
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===‘Food-web’ competition=== <br />
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[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
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Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11609Effects of fisheries on European marine biodiversity2007-08-31T15:44:54Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
SOURCE: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11608Effects of fisheries on European marine biodiversity2007-08-31T15:43:35Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
<br />
[[Image:Lophelia impact trawling.jpg|center|300px|'''Left''': ''Lophelia'' reef before trawling. '''Right''': ''Lophelia'' reef after trawling. Video photograph from the Norwegian continental break at 220 m depth (16 May 1998), showing a barren landscape with spread, crushed remains of ''Lophelia'' corals. This is an area that is subject to considerable bottom trawling. <br />
Source: Institute of Marine Research, Bergen, Norway<br />
|frame]]<br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=File:Lophelia_impact_trawling.jpg&diff=11607File:Lophelia impact trawling.jpg2007-08-31T15:39:24Z<p>Ltherry: </p>
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<div></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11606Effects of fisheries on European marine biodiversity2007-08-31T15:38:56Z<p>Ltherry: </p>
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<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
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Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
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Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
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Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
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Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
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===Direct effects on by-catch species===<br />
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Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
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Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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[[Image:Lophelia impact trawling.jpg|center|300px||frame]]<br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11605Effects of fisheries on European marine biodiversity2007-08-31T15:31:26Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
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<br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11604Effects of fisheries on European marine biodiversity2007-08-31T15:29:38Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
<br />
[[Image:food web competion.jpg|right|300px|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187. |frame]]<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
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<br />
<br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=File:Food_web_competion.jpg&diff=11603File:Food web competion.jpg2007-08-31T15:14:54Z<p>Ltherry: </p>
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<div></div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11602Effects of fisheries on European marine biodiversity2007-08-31T15:14:25Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
[[Image:food web competion.jpg|center|300px| |frame]]<br />
<br />
<br />
<br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11601Effects of fisheries on European marine biodiversity2007-08-31T15:02:49Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
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===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name="Jennings1998">Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability<ref name="Rhoads">Rhoads, D.C. (1974). Organism-sediment relations on the muddy sea floor. ''Oceanography and Marine Biology Annual Review'' 12: 263-300. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name="Moore1977"> Moore, P.G (1977). Inorganic particulate suspensions in the sea and their effects on marine animals. ''Oceanography and Marine Biology Annual Review'' 15: 225-363. '''cit. in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><ref name="Jones1992">Jones, J.B. (1992). Environmental impact of trawling on the seabed: a review. ''New Zealand Journal of Marine and Freshwater research'' 26: 59-67. '''cit. in''': Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks.<ref name="Walters1993">Walters, C.J. & Juanes, F. (1993). Recruitment limitations as a consequence of natural selection for use of restricted feeding habitats and predation risk taking by juvenile fishes. ''Canadian Journal of Fisheries and Aquatic Science'' 50: 2058-2070. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11600Effects of fisheries on European marine biodiversity2007-08-31T14:53:20Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name="">Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, in: Boyd, I.L. et al. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. Conservation Biology, 12: pp. 11-27.</ref><br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species.<ref name="Stokes1993">Stokes, T.K.; McGlade, J.M. & Law, R. (eds) (1993). The exploitation of Evolving Resources. ''Lecture Notes in Biomathematics, 99. Springer-Verlag'', Berlin. 264 pp. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Jennings1998">Jennings, S.; Reynolds, J.D. & Mills, S.C. (1998). Life history correlates of responses to fisheries exploitation. ''Proceedings of the Royal Society London series B'' 265: 333-339. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993)<ref name="Rijnsdorp1993">Rijnsdorp, A.D. (1993). Fisheries as a large-scale experiment on life-history evolution: disentangling phenotypic and genetic effects in changes in maturation and reproduction of North Sea plaice, ''Pleuronectes platessa'' L. ''Oecologia'' 96:391-401. '''cit in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref> carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name="Borisov1979">Borisov, V.M. (1979). The selective effect of fishing on the population structure of species with a long life cycle. ''Journal of Ichtyology'' 18: 896-904. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref><ref name="Law1989">Law, R. & Grey, D.R. (1989). Evolution of yields from populations with age-specific cropping. ''Evolutionary Ecology'' 3: 343-359. '''cit. in''': Law, R. (2000). Fishing, selection, and phenotypic evolution. ''ICES Journal of Marine Science'' 57: 659-668.</ref>. Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas.<ref name=""></ref> (1) <br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability .<ref name=""></ref> (12) and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name=""></ref>.<ref name=""></ref> (13) (14). <br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks..<ref name=""></ref> (15)<br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11599Effects of fisheries on European marine biodiversity2007-08-31T14:24:40Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> <br />
<br />
===‘Food-web’ competition=== <br />
<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name="Trites (1997)">Trites, A.; Christensen, V. & Pauly, D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal North West Atlantic Fisheries Science'' 22: 173-187. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12: 11-27.</ref> Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name=""></ref> (2)<br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species..<ref name=""></ref>.<ref name=""></ref> (18) (19) <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993).<ref name=""></ref> (20) carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name=""></ref>.<ref name=""></ref> (21) (22). Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas..<ref name=""></ref> (1) <br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability .<ref name=""></ref> (12) and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name=""></ref>.<ref name=""></ref> (13) (14). <br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks..<ref name=""></ref> (15)<br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11598Effects of fisheries on European marine biodiversity2007-08-31T14:20:41Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
===Direct effects of physical disturbance===<br />
<br />
The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
<br />
In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
<br />
Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
<br />
Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
<br />
Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan ''Pentapora foliacea'').<br />
<br />
<br />
==Indirect effects of fisheries==<br />
<br />
===Effects of ‘ghost-fishing’===<br />
<br />
When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties.<ref name="Carr1992">Carr, H.A.; Blott, A.J. & Caruso, P.G. (1992). A study of ghost gillnets in the inshore waters of southern New England. ''In “MTS” 92: Global Ocean Partnership''”, pp. 361-367. Marine Technology Society, Washington D.C. '''cit. in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
===Trophic cascading effect=== <br />
<br />
Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years.<ref name="Daskalov2002">Daskalov, G.M. (2002). Overfishing drives a trophic cascade in the Black Sea. ''Marine Ecology Progress Series'' 225: 53-63.</ref> (16) <br />
<br />
===‘Food-web’ competition=== <br />
<br />
An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name=""></ref> (17). Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name=""></ref> (2)<br />
<br />
===Effects on phenotypic evolution===<br />
<br />
Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
<br />
Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species..<ref name=""></ref>.<ref name=""></ref> (18) (19) <br />
<br />
There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993).<ref name=""></ref> (20) carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
<br />
The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name=""></ref>.<ref name=""></ref> (21) (22). Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
<br />
===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
<br />
===Indirect effects of physical disturbance===<br />
<br />
The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas..<ref name=""></ref> (1) <br />
<br />
The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability .<ref name=""></ref> (12) and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name=""></ref>.<ref name=""></ref> (13) (14). <br />
<br />
Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks..<ref name=""></ref> (15)<br />
<br />
==References==<br />
<br />
<references/><br />
<br />
{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherryhttps://www.coastalwiki.org/w/index.php?title=Effects_of_fisheries_on_European_marine_biodiversity&diff=11597Effects of fisheries on European marine biodiversity2007-08-31T14:16:20Z<p>Ltherry: </p>
<hr />
<div>Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257.</ref><br />
<br />
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [[bottom trawling]]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [[piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
<br />
<br />
==Direct effects of fishing==<br />
<br />
===Direct effects on target species===<br />
<br />
Global landing of fish and other marine catches began stagnating in the early 1980s.<ref name="Watson2001">Watson, R. & Pauly, D. (2001). Systematic distortion in world fisheries catch trends. ''Nature'' 414 (6863): 534-536.</ref> Biomass in the North Atlantic fell by 90 % during the twentieth century, leading to declines of catches throughout the North Atlantic, notably in eastern Canada. It has taken less than a century for North Atlantic fisheries to reduce the biomass of the high-trophic-level fishes to under 10% of their original amounts.<ref name="">Christensen, V.; Guénette, S.; Heymans, J.J. ''et al''. (2003). Hundred-year decline of North Atlantic predatory fishes. ''Fish Fisher'' 4: 1-24. '''cit. in''': Trites, A.W.; Christensen, V.; Pauly, D. (2006). Effects of fisheries on ecosystems: just another top predator?, '''in''': Boyd, I.L. ''et al''. (Ed.) (2006). Top predators in marine ecosystems: their role in monitoring and management. ''Conservation Biology'' 12:11-27.</ref><br />
<br />
Historically, fishing started at the top of most food chains by removing the highly valuable and more easily cacheable species, then moved down to the next biggest species as those above were depleted and were no longer easily or economically caught. The downward shift towards fish catches of lower trophic levels results in ‘fishing down the food web’. The mean trophic level of reported catches had declined over the years. For all marine areas, the trend has been a decline in the mean [[trophic level]] of the fisheries landings form slightly more than 3.3 in the early 1950s to less than 3.1 in 1994.<ref name="Pauly1998">Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. ''Science'' 279: 860-863.</ref> <br />
<br />
Another shift in the global landings of fishes in the last 50 year is from shallow to deeper water species; this resulted in the fact that the mean longevity of the fish species caught, has increased dramatically. This trend is a serious concern because species with larger body size, longer life span, later sexual maturity and slow growth (e.g. Dogfish ''Scyliorhinus canicula'', Rays, Conger eel ''Conger conger'') are more vulnerable to overfishing.<ref name="Morato2006">Morato, T.; Watson, R.; Pitcher, T., J. & Pauly, D. (2006). Fishing down the deep. ''fish and fisheries'' 7: 24-34.</ref><br />
<br />
===Direct effects on by-catch species===<br />
<br />
Benthic organisms and other unwanted by-catch are often discarded and a range of species are killed, but not retained by towed gears. <br />
<br />
Some by-catch species have been affected dramatically by fishing. For example, the population sizes of three dolphin populations (a ''Stenella longirostris'' population, a ''S. attenuata'' population and a second ''S. longirostris'' population) caught by tuna boats in the eastern tropical Pacific were reduced to 20%, 35-50% and 58-72% of pre-exploitation levels by 1997: 2.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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===Direct effects of physical disturbance===<br />
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The direct effects of fishing, related to physical disturbance include the scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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It seems reasonable to predict that the effects of physical disturbance will be short-lived in communities adapted to frequent natural perturbations (e.g. a cockle community) in contrast to those communities found in habitats exposed to fewer disturbances (e.g. the abyssal plane).<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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The changes associated with physical disturbance are relatively short-lived for the majority of small species, longer-lived organisms decolonize more slowly. For example, Beukema (1995) reported that the biomass of gaper clams, ''Mya arenaria'' L., took 2 year to recover after lugworm dredging in the Wadden Sea, whereas small polychaetes and bivalves had recolonized the dredged areas within 12 months.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Communities dominated by long-lived suspension feeders are most likely to be replaced by a community of opportunistic deposit-feeding species and mobile epifauna when subjected to large-scale and intense fishing disturbance. More dramatically, biogenic structures that increase the complexity of the epibenthic habitat (e.g. worm tubes) create specialized environmental conditions by altering local hydrographic conditions that encourage the development of a specialized associated community. Loss of such structures will also affect the survivorship of any associated species and prolong the recolonisation process.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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A particular sensitive hard-bottom habitat is the deep-water coral (the basis for the reef formation is ''Lophelia pertusa'') communities. These communities are mainly found at the offshore shelf edges of the [[Arctic]] and [[North-Atlantic ocean]]. Some offshore reefs have experienced considerable damage due to trawling activities. The ''Lophelia'' reefs have recently (since 1999) been protected from fishing activities by the Norwegian authorities.<ref name="EEA2002">''EEA report'' (2002). Europe’s biodiversity – biogeographical regions and seas – biogeographical regions in Europe – The Arctic Ocean</ref><br />
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In soft mud communities a large proportion of the fauna live in burrows up to 2 m deep.<ref name="Atkinson1990">Atkinson, R.J.A. & Nash, R.D.M. (1990). Some preliminary observations on the burrows of ''Callianassa subterranean'' (Montagu) (Decapoda: thalassinidae) from the west coast of Scotland. ''Journal of Natural History'' 24: 403-413. '''cit in''': Jennings, S. & Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> Few of these deep burrowing fauna are likely to be affected by passing trawls. However, the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals. <br />
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Sessile epibenthic species are most likely to be vulnerable to the passage of bottom gears. The disappearance of reefs of the calcareous tube building worm, ''Sabellaria spinulosa'' Leukart and their replacement by small polychaete communities, indicated that dredging activity had caused measurable changes in the Wadden Sea benthic community.<ref name="Riesen1982">Riesen, W. & Riese, K. (1982). Macrobenthos of the subtidal Wadden Sea: reveisited after 55 years. ''Helgolander Meeresuntersuchungen'' 35: 409-423. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref> <br />
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Changes attributed to the fisheries are identified in the mesozooplankton composition. For instance, the mezozooplankton taken in continuous plankton recorder samples in the central North Sea were numerically dominated by calanoid copepods from 1958 to the late 1970s, whereas samples taken from the same stations from the early 1980s to early 1990s were dominated by the pluteus larvae of echinoid and ophiuroid echinoderms. This trend is consistent with the reported increases in the abundance of echinoderms in benthic communities which may have been stimulated, in part, by bottom trawling.<ref name="Lindley1995">Lindley, J.A.; Gamble, J.C. & Hunt, H.G. (1995). A change in the zooplankton of the central North Sea (55° to 58°N): a possible consequence of changes in the benthos. ''Marine Ecology Progress Series'' 119: 299-303. '''cit in''': Jennings, S.; Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352.</ref><br />
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Static bottom gears are anchored to the seabed and left to fish passively. The most commonly used are gill, trammel or tangle nets, which are designed to capture target species by enmeshing or tangling them.<ref name="Miller1977">Miller, R.J. (1977). Resource underutilization in a spider crab industry. ''Fisheries'' 2: 9-13.</ref><ref name="Potter1991">Potter, E.C.E. & Pawson, M.G. (1991). Gill netting. ''Laboratory leaflets, MAFF, Directorate of Fisheries Research, Lowestoft'' 69, 34pp.</ref><br />
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Net and pot fisheries are static, for this reason , the areas of seabed affected by each gear is insignificant compared with the widespread effects of mobile fishing gears. However, effort may be significant if concentrated in relatively small areas with communities of long-lived fauna (e.g. the foliose bryozoan Pentapora foliacea).<br />
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==Indirect effects of fisheries==<br />
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===Effects of ‘ghost-fishing’===<br />
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When nets or catch-pots are lost, they may continue to fish. This phenomenon is known as ‘ghost-fishing’. In circumstances where nets or pots are snagged onto rocks, holding the net in place, or lost in deep water in relatively stable environment, they may continue to fish indefinitely. In these cases, a typical pattern of capture is observed. Over the first few days, catches decline almost exponentially as the increasing weight of catch causes the net to collapse. Then, for the next few weeks, the decaying bodies of fishes and Crustacea attract large number of scavenging crustaceans, many of which are valuable commercial species and also become entangled in the net. Thereafter, there appears to be a continuous cycle of capture, decay and attraction for as long as the net has some entanglement properties..<ref name=""></ref> (11)<br />
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===Trophic cascading effect=== <br />
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Changes in one level of a food web can also have cascading effects on others. For example in the Black Sea, a trophic cascade has acted by fishery removals of apex predators (bonito ''Sarda sarda'', mackerel ''Scomber scombrus'' , bluefish ''Pomatomus saltatrix'', dolphins) which caused a decreased consumer control and lead to higher abundance of planktivorous fish (i.e. Black Sea sprat ''Clupeonella cultriventris'', anchovy ''Engraulis encrasicholus'', horse mackerel ''Trachurus mediterraneus ponticus''). The increased consumption by planktivorous fish causes a decline in zooplankton biomass that in turns allowed phytoplankton to increase. This chain of events is thought to explain the explosions of phytoplankton and jellyfish reported in the Black Sea over the past 30 years..<ref name=""></ref> (16) <br />
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===‘Food-web’ competition=== <br />
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An apex predator may be affected by fisheries even when the prey and species caught do not overlap. This has been termed ‘food-web competition’.<ref name=""></ref> (17). Food-web competition occurs when there is potential overlap of the trophic flows supporting a given group (e.g. marine mammals) with the trophic flows supporting another group (e.g. fisheries). The relationship between the size of fishery catches and the amounts of primary production required to sustain fisheries and marine mammals suggests that the primary production available to marine mammals may decline as catches increase.<ref name=""></ref> (2)<br />
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===Effects on phenotypic evolution===<br />
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Large changes in size-at-age and age-at-maturation of commercially exploited fish have been reported in a number of ecosystems. Survival and reproduction are functions of body size. Small fish generally incur higher mortality rates and produce fewer eggs than larger fish.<br />
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Gear is designed to remove some kinds of individuals in preference to others, usually individuals that are larger and, indirectly, older. The location of fishing is often non-random relative to spatial distributions of stocks, being concentrated where the harvestable biomass is greatest or where fishes are most accessible, or both. Fishing mortality is therefore selective with respect both to species and to phenotypic variation within species..<ref name=""></ref>.<ref name=""></ref> (18) (19) <br />
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There are strong indications that the observed changes have partly a genetic basis. Although, it is difficult to distinguish evolution on the genetic level, from plasticity in life-history traits, i.e., a tendency of these traits to take different values depending on the current environmental conditions. Rijnsdorp (1993).<ref name=""></ref> (20) carried out a study to disentangle the causes of a major phenotypic change in maturation of North Sea plaice (''Pleuronectes platessa''). He concluded that a substantial part of the change in maturation is consistent with genetic change caused by fishing. Simply through the action of fishing, fisheries generate selection, causing evolution in life-history traits.<br />
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The common trend is an increased size-at-age and a decreased age-at-maturation in heavily exploited fish stocks, but this selection pattern is not always consistent. For instance, there are two spatially separated Arctic cod (''Arctogadus glacialis'') fisheries operating in the Barents Sea: a feeder (exploitation of the stock on the feeding grounds) and a spawner fishery (exploitation of the stock on the spawning grounds). Fishing confined to the spawning grounds, gives an advantage to late maturation. This is because the extra mortality due to fishing on the spawning grounds makes it advantageous to grow for longer before maturation and thereby to produce more eggs when risking a visit to the spawning ground. If fishing mortality on the feeding grounds is added on, the relatively small advantage to late maturation is changed to a large advantage to early maturation.<ref name=""></ref>.<ref name=""></ref> (21) (22). Remaining on the feeding grounds is now itself risky, and a fish that does not mature until about, 8 years old is most likely to be caught before it spawns. <br />
Current patterns of fishing generate strong selection for early maturation and, given appropriate genetic variation, substantial genetic change can be expected. But, if one were to try to reverse the process by closing the fishery, selection for later maturation would be weak. In other words, it could be hard to undo the effects of inadvertent selection caused by fishing. <br />
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===[[Living_resources#Impact_of_discard|Impact of discard]]===<br />
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===Indirect effects of physical disturbance===<br />
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The resuspension, transport and subsequent deposition of sediment may affect the settlement and feeding of the biota in other areas..<ref name=""></ref> (1) <br />
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The potential effects of sediment resuspension include clogging of feeding apparatus or reduction of light availability .<ref name=""></ref> (12) and sediment deposition has been shown to inhibit the settlement and growth of oysters and scallops.<ref name=""></ref>.<ref name=""></ref> (13) (14). <br />
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Mobile gears effects the epifauna by modification of substrata and removal of biogenic concretions and a consequent decline in the abundance of fauna associated with them. The loss of biogenic species not only reduces the supply of important prey species, but also increases predation risk for juvenile commercial species thereby lowering subsequent recruitment to the adult stocks..<ref name=""></ref> (15)<br />
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==References==<br />
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<references/><br />
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{{author<br />
|AuthorName=Therry, Lieven}}<br />
[[Category:Theme 7]]</div>Ltherry