Harbour porpoise in the Belgian part of the North Sea

Introduction

The harbour porpoise (Phocoena phocoena) is one of the smallest species of the cetacean family. This species is part of the group of the toothed whales (Odontoceti), which forms the order of the cetaceans together with the baleen whales (Mysticeti). The harbour porpoise belongs to the more general family of the porpoises (Phocoenidae), which are distributed worldwide in cold and temperate waters. Harbour porpoises are distributed in the Northern Hemisphere where they feed on sandeels and whiting which are found on the seabed mostly in areas of strong tidal currents (see below). The North Atlantic harbour porpoise (P. phocoena phocoena) is one of the three subspecies of the harbour porpoise. The other two subspecies are the North Pacific harbour porpoise (P. phocoena vomerina) and the Black Sea harbour porpoise (P. phocoena relicta). They are mostly spotted alone or in mother-calf pairs. Despite being a top predator itself, the harbour porpoise is reported to be scavenged by seals and other cetacean species and actively predated by the grey seal (Halichoerus grypus) (Haelters et al, 2012 240684; van Bleijswijk et al., 2014 265788; Bouveroux et al., 2014 279005; Jauniaux et al., 2014 271626; Leopold et al., 2015 267365). Until the beginning of the 20th century harbour porpoises were exploited for their oil and flesh in the North Sea (Lotze, 2007 125854).

In the last years the frequency of sightings of porpoises in the southern North Sea has increased, a trend which is mainly explained by a southward shift in their distribution area in the North Sea. This shift is in line with other findings such as the shift in distribution of prey fish which are becoming more abundant in the Southern North SeaBelgian marine waters (BPNS). It is therefore important for managers, policy- and decision-makers and professionals who work in the marine environment to rely on the best available scientific information about the distribution, biology and ecology of the harbour porpoise in the BPNS and adjacent areas. The harbour porpoise is included on Annex XXXX habitat directive and is key or indicator species in a number of legal instruments oriented towards an improved environmental status (e.g. Marine Strategy Framework Directive). This information is therefore highly relevant in the context of conservation, monitoring and evaluation of the harbour porpoises populations that frequent the BPNS.. Although the information on the harbour porpoise is very exhaustive, specific information for the BPNS is less abundant and often scattered.

The present document attempts to gather the scientific information on the harbour porpoise (Phocoena phocoena) the harbour porpoises and its distribution in the Belgian waters and the (Southern) North Sea. It also provides a structured overview of the available research with a main focus on the Belgian part of the North Sea. This document addresses four main topics.