Harbour porpoise  (Phocoena phocoena)

The harbour porpoise is the most commonly seen porpoise (1), and is the most widely distributed of all cetaceans (whales and dolphins) in northern Europe (5). It is easily recognised as it has a low triangular dorsal fin and lacks a beak (1). It is small in comparison to other porpoises, has a plump body with a dark grey to bluish coloured back, a pale belly and a rounded head (4). At birth, young harbour porpoises are dull in colour and typically have 'birth lines', which look like folds in the skin, and persist for the first few hours after birth (4).

Found in subarctic and cool temperate waters of the North Atlantic and North Pacific (4). Although typically a species of coastal areas, the harbour porpoise also occurs over most of the European continental shelf (5). In the UK, seasonal concentrations occur between July and October off western and south-western Ireland, west Wales, the west of Scotland, around Shetland and Orkney as well as around north-east Scotland (5). This species used to occur in the south coast of England and southern parts of the North Sea, but it is now rare in these waters (5).

Favours shallow, cold coastal waters (5). Most sightings have been made within 10km of the land. It frequents relatively shallow bays, estuaries, and tidal channels under about 200km in depth, and will swim a considerable distance up river (6).

A social species, the harbour porpoise travels in groups numbering between 2 to 5 individuals (1), but larger groups may form during migration (5). It feeds on a variety of fish, including herring, mackerel and anchovy (1), a variety of invertebrates are also taken (5). It is known that echolocation is used in the detection and capture of prey, but this is not yet fully understood. Sight and passive listening (for the sounds made by prey) are also important during hunting (2). Mating occurs in summer, and gestation (pregnancy) takes 11 months (5). The calf is suckled for up to 8 months and sexual maturity is reached at about 4 years of age (5). The harbour porpoise has possibly the shortest life-span of any cetacean; they rarely live for more than 12 years (1).

Since the 1940s, there is evidence of a decline in the numbers of this species in UK waters (3). The main threats are thought to include entanglement in fishing nets, chemical and noise pollution, hunting, boat traffic, and lack of food (4).

A UK Biodiversity Action Plan priority species, the harbour porpoise is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders, 1985; it is illegal to intentionally kill, injure, or harass any cetacean (whale or dolphin) species in UK waters (3). The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS) has been signed by 7 European Countries, this includes the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness (2). Increased awareness of this species may help to secure its future (1).

For more on this species see the WDCS species guide, available on-line at:
http://www.wdcs.org/dan/publishing.nsf/allweb/0216015652588B3C802568F8004E7AF5 For more on whales and dolphins see the WDCS homepage:
http://www.wdcs.org/

Information authenticated by WDCS, the Whale and Dolphin Conservation Society:
http://www.wdcs.org