Harbour Porpoise (Phocoena phocoena) - Species Action Plan

Ref 1/S4 Species Action Plan 4
Plan Author: Norfolk County Council
Plan Co-ordinator: Coastal BAP Topic Group
Plan Leader: Eastern Sea Fisheries Joint Committee
Date: 31 December 1998
May 2007 Revised Final Draft

Action Plan Summary

Current Status

National Status

  • The harbour porpoise is predominantly a coastal species, favouring shallow waters over the continental shelf. It is limited to the cold temperate and subarctic waters of the Northern Hemisphere. In the eastern North Atlantic it ranges from Iceland south to the coasts of Senegal, including the North Sea, the Baltic Sea and the western Mediterranean.
  • There is some evidence of a decline in the numbers of harbour porpoise in the UK since the 1940s. However, generally the conservation status around the UK is poorly known. The SCANS (Small Cetacean Abundance in the North Sea and adjacent waters) surveys, coordinated by the Sea Mammal Research Unit (SMRU) in July 1994, provided the first population estimates of harbour porpoises and other small cetaceans around the UK, including the North Sea. The surveys estimated a total harbour porpoise population in the North Sea, English Channel and Celtic Sea of approximately 340,000 (Hammond et.al. 1995). An estimate of abundance in the eastern sector of the North Sea between the North Norfolk coast and the north-east coast of Scotland was 16,900 animals (Hammond et.al. 2002). In the 1994 SCANS survey no porpoises were recorded in the North Sea south of the Wash. The SCANS surveys were repeated in July 2005 and preliminary results have shown an increase in the density of porpoises in the southern North Sea, including the Norfolk sector (Macleod et al 2006).
  • The harbour porpoise is listed on Appendix II of the Bern Convention and Annexes II and IV of the EU Habitats Directive. It is on Appendix 2 of the Bonn Convention and is covered by the Agreement on the conservation of small cetaceans in the Baltic and North Seas (ASCOBANS), a regional agreement of the Bonn Convention. It is protected under schedule 5 of the Wildlife and Countryside Act 1981 (As amended by the Countryside and Rights of Way Act 2000). No SACs have currently been designated for this species.

Norfolk Status

  • Found off the Norfolk coast. The local status is poorly known, but anecdotal sighting records and stranding data indicates that harbour porpoises were previously more common in Norfolk waters and that the population declined during the middle part of the twentieth century (Seago 1992, 1997). However, in the last decade, there has been an increase in sightings and strandings along the entire Norfolk coast, with a peak in records during the winter and early spring (Jan-April).
  • Similar increases have been noted in neighbouring Dutch waters. Porpoises were virtually extinct in Dutch coastal waters in the early 1960s, but systematic annual land-based and at-sea surveys carried out since 1970 have shown significant increases in sightings and strandings since the mid-1980s, with a marked increase in records over the last 15 years (Camphuysen 2004).

back to top

Current factors affecting the habitat in Norfolk

There are several factors affecting the status of this species:

  • Bycatch: Accidental capture in fishing nets is considered to be a major threat to this species around the UK (UK BAP). Harbour porpoises are particularly vulnerable to bottom-set gillnets because they tend to feed at, or close-to, the seabed. During the early 1990s, it was estimated that 7,000 harbour porpoises were caught annually in the Danish North Sea gillnet fishery, and 1,000 in the UK gillnet fishery. The latter figures represent more than 2% of the total porpoise population in the central and southern North Sea. According to the International Whaling Commission and ASCOBANS, continued bycatch at this rate is likely to be unsustainable.
  • Environmental contaminants (toxic substances at sea, marine debris, disease and noise disturbance): Contamination of the marine environment by anthropogenic input has increased dramatically over the last 50 years. Many of the contaminants which give the greatest cause for concern (e.g. PCBs) are relatively poorly metabolised or excreted by animals. As predators at the top of the food chain, harbour porpoises are very susceptible to the build-up of such contaminants.
  • Environmental change (effects of fishing and possibly climate change): In UK waters, Evans (1990) has suggested that the decline in porpoise numbers during the latter part of the 20th century was due to the depletion of herring stocks. It has also been suggested that the decline in harbour porpoise strandings along the Dutch coast may have been caused by changes in the herring stocks through overfishing, particularly in the mid-1960s (Smeenk & Addink 1990). The increase in the North Sea herring stock in recent years may be one of the reasons for an increase in sightings of harbour porpoises in the south-eastern North Sea (Camphuysen 1994).
  • Disturbance: Disturbance from boat traffic is thought to be increasing, as boat-based leisure activities become more popular. Porpoises are prone to disturbance of two principal types: 1) Physical disturbance: Vessels cause disturbance, and fast craft can potentially cause physical injury through collisions; 2) Noise disturbance: Noise travels far underwater, and noise from boat engines and echosounders may cause disturbance to porpoise activities or mask porpoise echlochation. In the long-term, areas of high boat traffic may be avoided by porpoises, potentially excluding them from important feeding or calving areas.

Offshore windfarms may potentially impact on populations of harbour porpoises and other cetaceans. The precise impact of offshore windfarms on harbour porpoises is currently not fully understood. Impact may be positive, creating artificial reefs around the moorings, which could increase fish abundance; or negative, with displacement of prey species or porpoises themselves due to disturbance. This disturbance may be acoustic if there is transmission of sound or vibrations from the rotating blades into the water. 

back to top

Current Action in Norfolk

  • Post mortems and tissue studies are carried out by the Natural History Museum (London) on stranded specimens to establish the cause of death and condition of the animals at the time of death.

back to top

Action Plan Objectives and Targets

National

  • Maintain the current geographical range of the harbour porpoise.
  • Maintain the current abundance of the harbour porpoise.
  • In the long-term, ensure that no anthropogenic factors inhibit a return to waters that it previously occupied.

Norfolk

  • Ensure that the local populations of harbour porpoise are maintained and enhanced.

back to top