Northern Ireland's Priority Species

Phocoena phocoena – harbour porpoise

Phocoena phocoena

Phocoena phocoena L., 1758
Family: Phocoenidae

The harbour porpoise is the smallest and most common cetacean (whale/dolphin) found in the coastal waters of Northern Ireland. The population is believed to have decreased over the last 50 years – this may be due in part to thousands of porpoises getting caught and drowning in commercial fishing nets every year around the UK coast.

In brief

  • Found in the seas around Northern Ireland

  • Can be seen all year round

  • Listed as a UK Priority Species

  • Main threats to the population are accidental capture and drowning in commercial fishing equipment (by-catch) and pollution.

Species description
The body is short and rounded – adults are usually between 1.5 and 1.9m long. The back is dark grey/black and the belly is pale/white. The pale markings extend up the sides above the flippers. A dark line runs from the mouth to the flippers. The head is small and rounded, there is no beak. There are numerous spade-shaped teeth present in the upper and lower jaw. The small, triangular dorsal fin is in the middle of the back.

The blow is short and usually not visible but can often be heard, giving rise to the name ‘puffing pig’.

Life cycle
A coastal species found only in the cool temperate and sub-polar waters of the Northern Hemisphere. Present all year round in many areas. Some populations, however, move inshore in summer and offshore in winter; these seasonal movements may be due to food availability and breeding. Porpoises become sexually mature between two and four years of age. Pregnancy lasts about 10 to 11 months and a single calf may be produced every 1 to 2 years. Calves are born during the summer. The average life span is between 12 and 15 years. Porpoises are usually seen in small groups of two or three, but where feeding is good, 20 to 30 animals may be seen together. They feed mainly on small shoaling fish such as herring, mackerel and sand eels but will also take squid and octopus. Harbour porpoises are capable of diving to depths of 200m and can stay underwater for up to six minutes.

Similar species
Unlikely to be confused with any other species due to their small size. There is less surface activity than with dolphins – usually only the back and dorsal fin is seen and there is very little splashing. Porpoises are slow swimmers, tend to avoid boats and do not bow ride.

How to see this species
Sightings off the coast of Northern Ireland are common at all times of the year. The best places to see harbour porpoises are headlands and bays when the sea is calm. Feeding seabirds may help pinpoint their location.

Current status
Harbour porpoises are seen regularly in the seas around Northern Ireland. A 1994 survey of small cetaceans in the North Sea, English Channel and Celtic sea (SCANS) estimated the population of harbour porpoise to be around 350,000. Current population estimates are not known; however, the results of a new small cetacean survey (Scans II) will be available in 2006.

  • Protected under schedule 5 of the Wildlife (Northern Ireland) Order 1985

  • Listed in Annex A of EU Council Regulation 338/97 and therefore treated by the EU as if they are on CITES, Appendix I, thus prohibiting their commercial trade

  • Listed on Appendix II of CITES

  • Listed in Appendix II of the Convention on the Conservation of Migratory Species (The Bonn Convention)

  • Covered by the terms of The Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS)

  • Listed in Appendix II of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention)

  • Classified as Vulnerable on the IUCN 2002 Red List

  • Listed in Annex II and IV (Animal and Plant Species of Community Interest in Need of Strict Protection) of the EC Habitats Directive.

Why is this species a priority in Northern Ireland?

  • Listed as a UK Priority species

Threats/Causes of decline
By-catch – the accidental killing associated with commercial fishing equipment – trawls, seines, cod traps and, in particular, bottom-set gill nets are the biggest threat to harbour porpoise populations.

Other threats include disturbance and injury by speedboats and jet skis, climate change and ocean pollution (chemical and noise).

Whales and dolphins communicate mainly by sound; they also use sound to navigate and find food. Many man-made sounds are introduced into the oceans, some of these, such as noise due to seismic exploration for oil and gas and disturbance from marine traffic, may pose a threat to whales and dolphin populations.

Many species of fish eaten by porpoises are also fished commercially (herring, mackerel, sprat, pilchard, whiting, cod). Reduction in fish numbers due to commercial fishing may threaten porpoise populations.

Conservation of this species

Current action
There is a UK Species Action Plan for this species which was published in 1999.

  • Post-mortem and tissue studies of stranded corpses are carried out to establish the cause of death and condition of the animals at the time of death.

Proposed objectives/actions

  • Maintain the current geographical range of the harbour porpoise

  • Maintain the current abundance of the harbour porpoise.

What you can do
To report harbour porpoise sightings contact CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, Tel: 028 9039 5264, [at]

Further information

The Wildlife (Northern Ireland) ) Order 1985.

UK Species Action Plan – Harbour Porpoise

Irish Whale and Dolphin Group

ARKive – Harbour Porpoise

Northern Ireland's Mammals, Amphibians & Reptiles


Text written by:
Angela Ross, Curator of Vertebrates, Ulster Museum

iNaturalist: Species account : iNaturalist World Species Observations database