Harbour porpoise

Harbour porpoises (Phocoena phocoena) are the smallest cetaceans to swim in the open sea. Adults are about 1.5m to 1.6m in length. Females are about 10 to 15cm longer. Harbour porpoises have a dark grey body with a pale ventral surface. There's often a striking grey line from just below the eyes to the back edge of the flipper. They have 19 to 28 small, spade-shaped teeth on each of the upper and lower jaws.

Harbour porpoises are seen in small groups of less than ten animals, although larger groups are sometimes seen in good feeding areas or when they are migrating.

Where are they found?
The harbour porpoise is found in the shallow, cold temperate and sub-arctic waters of the Atlantic coast of Europe, east and west coasts of North America and the Pacific coast of Asia. They are common in the North Sea and Danish Wadden Sea. Around Norway, there are around 11,000 porpoises in the Lofoten Islands in the Barents Sea region, and 82,000 in the northern North Sea.

Harbour porpoises have almost disappeared from the Baltic, and the winter migration between the Baltic and North Seas has stopped. In summer, the species has been recorded as far north as the southern coast of Baffin Island in Canada. The harbour porpoise seems to avoid polar waters, but can be seen in the summer off Greenland and along the Labrador coast.

In the eastern Pacific, they are found as far north as Point Barrow and Prince William Sound, Alaska. In the western Pacific, they have been recorded in the Bering Sea, Kamchatka, and the Sea of Okhotsk.

What do they eat?
Harbour porpoises primarily eat small schooling fish such as herring, mackerel, pollock and sardines. They also prey on squid and octopus, crustaceans, molluscs and polychaete worms. They eat up to ten percent of their body weight every day.

How long do they live?
Harbour porpoises reach sexual maturity when they are between three and six-years-old. Mating occurs in the summer, and females carry calves for about a year. Birth normally takes place between May and August, but births have been reported as early as March in Norwegian waters. Calves nurse for around eight months and are then weaned. Females have calves every one to two years. From tooth data, the maximum reported age of a harbour porpoise is 24. Harbour porpoises suffer predation by sharks and killer whales.

Conservation concerns
Harbour porpoises are impacted by human activities and habitat disturbance. Thousands of harbour porpoises worldwide are killed each year through by-catch. Declines in porpoise populations in some regions may also be directly related to habitat loss and prey depletion from commercial over-fishing.

Harbour porpoises may also be negatively impacted by toxics, including hydrocarbon compounds, insecticides such as DDT, PCBs, dioxins and heavy metals. Links have been suggested between levels of pollutants and impacts on reproduction and immune function in other species of marine mammals.