The harbour porpoise is the most commonly seen porpoise in shallow coastal waters, estuaries, bays and river mouths. It is recognizable by its short triangular dorsal fin, blunt snout (unlike the pointed ‘nose’ of dolphins) and no distinct forehead. They are small and stocky, with a dark grey back and lighter underbelly.

Behaviour

Harbour porpoise appear to favour the continental shelf, but may make seasonal movements to the coast often connected with the feeding of calves in shallower waters in early summer.

They usually swim close to the water’s surface, rising up every 25-30 seconds to breathe. They do not present an especially playful attitude, unlike dolphins, but can often be detected by their sneeze-like puffing sound as they breathe at the surface. They also exhibit a characteristic slow rolling surfacing motion.

Harbour porpoises are generally solo foragers but have been known to hunt in small groups. They have small spade-shaped teeth which are used to grab their prey, which is swallowed whole. A typical diet consists of fish (herring, cod, hake and sardines), squid and crustaceans.

Harbour porpoises are polygynandrous, i.e., two or more males mating with two or more females. Females become sexually mature at around three or four years and give birth to a single calf every year, or every other year for a number of years. Birthing occurs around early summer (June/July). The young are between 65 and 85 cm long at birth and weigh 6.5-10 kg. Calves are weaned after 8-12 months, but stay with their mothers for a further eight to nine months.

Size

• Length: 1.4-1.9 metres
• Weight: 55-70 Kg
• Average lifespan: 12 years; can live to more than 20 years.

Status

Harbour porpoise is protected in the UK under the Wildlife and Countryside Act, 1981. In 2016, a Marine Protected Area, or Special Area of Conservation (SAC), was established by the Scottish Government in the Inner Hebrides and Minches, an area known as a hotspot for harbour porpoise in west Scotland. This area will offer some protection from a number of threats, ranging from over-fishing to pollution, including noise pollution. A total of 13,800 km² is now protected, supporting over 5,000 individuals.

Distribution

The harbour porpoise is widespread throughout the cold and temperate seas of Europe, including the North Sea, the Irish Sea, seas west of Ireland and Scotland, northwards to Orkney and Shetland. In fact, over 90% of the global population is found in UK waters. Harbour porpoises are the only species of porpoise found in Scotland; they are widespread – but their numbers are in decline.

When to see

January to December; in Scotland; seen all year round with a peak in summer.

Facts

• The word “porpoise” descends from a Medieval Latin word porcopiscus which is a compound of porcus meaning “pig” and piscus meaning “fish”.
• The harbour porpoise is equipped with echolocation, which enables it to navigate the seas and search for food in complete darkness.
• Harbour porpoises are the smallest species of cetacean found in Scottish waters, generally less than two metres long.
• Harbour porpoises eat about 10 percent of their body weight each day. They are warm-blooded mammals and their small size means they have to feed constantly to keep up their body temperature.