Harbour Porpoise

Phocoena phocoena

Key Facts

Gaelic Name: Muc-bhiorach

Length: Up to 1.8 metres (females slightly larger than males)

Range: Coastal waters of North Atlantic and Pacific

Threats: Caught in fishing nets, pollution

Diet: Variety of fish, shrimps and squid

Life Span

Of all cetaceans they have the shortest lifespan.  Capable of reaching up to 20 years, but rarely do, the average life is around ten.  Sexual maturity is reached at three to four years with females gestating for approximately 11 months.  Only one calf is born annually, which means the porpoises reproductive life is extremely short.  Calves are born at around 70 centrimetres long and have a strong bond with their mother.  Males play no part in the upbringing of the offspring.  Weaning can ocur quickly and individuals as young as six months have been known to become independent.  With such a short lifespan and reproductive life harbour porpoises are highly susceptible to sudden decreases in local populations.

Behaviour

The harbour porpoise is the most widespread, commonly seen and studied of all porpoises. They are very shy animals and only show their backs and dorsal fin when surfacing the water. One of the harbour porpoises names, the puffing pig, is derived from the noise of its blow when they surface the water for air. The noise made sounds like a human sneezing or puffing.

Feeding

Living in cool temperate waters the porpoise has a high metabolic rate, therefore the less choosy they are with their diet, the more successful they will be finding a meal.  Their diet consists of over 20 different species of fish, squid, octopus and shellfish.  Herring, sprat and sandeels make up a large part of the diet porpoises around the Isle of Mull and the small Isles.  They hunt singly or in small groups, usually including 2 to 10 individuals.  They are quite accomplished divers and when feeding may surface to breathe about four times every 10 to 20 seconds before diving for up to six minutes.  They can reach dpths of over 230 metres.  As with whales and dolphins they use echolocation when exploring the surrounding environment.  Porpoises are also hunted themselves, by larger predators in the waters of the Hebrides, these are killer whales, which also hunt their prey in packs.

Current Situation

Around the whole of the British coast, at least 10,000 porpoises are dying every year as a result of being mistakenly caught in fishing nets, mono-filament gill-nets.  They drown and are usually already dead when hauled aboard. This by-catch, scientists believe, is not sustainable and will certainly be damaging to future populations of British harbour porpoises.  Pollution is possibly the most serious long term threat faced by porpoise and other marine animal, populations, as we still do not fully understand the problems which marine pollution will bring in the future.

Distribution

Top of page