Identification at a glance
- No beak – rounded head
- Up to 1.8 m long
- Small, triangular dorsal fin with straight back edge, i.e., not hooked or ‘falcate’
(the shape of the dorsal fin does vary slightly between individuals, with some having a subtly more curved trailing edge, but the dorsal fin is much smaller than that of a dolphin).
- Grey back with lighter sides
- Dark flippers
- Mostly seen alone or in small groups. At some feeding grounds, gatherings of hundreds have been recorded (Carwardine, 2000).
Harbour porpoise are found in cold temperate to sub-polar waters of the Northern Hemisphere.
Harbour porpoise are largely limited to continental shelf waters and are most regularly found in relatively shallow bays, estuaries, and tidal channels less than about 200 m in depth (IUCN).
Diet – Fish, especially small schooling fish, and cephalopods, are their main prey items.
Harbour porpoise typically keep a low profile in the water. In many places, they are seen to swim slowly and travel alone or in small groups. This behaviour is also observed in Fishguard Bay. However, when at nearby Strumble Head, the porpoise are a bit different – they swim fast, leap out of the water and often congregate in large feeding groups during key stages of the tide. This behaviour is possibly related to the tide race around Strumble Head creating a rich feeding ground.
Fun fact: Harbour Porpoise can dive for as long as six minutes.
The main threats are thought to include entanglement in fishing nets, chemical and noise pollution, hunting, boat traffic, and lack of food. The most significant threat in most areas is incidental catches in fishing gear, primarily gill nets.
Incidental mortality in fishing gear is likely to occur throughout the species range (IUCN). Substantial incidental takes have been documented in areas including the North Sea (4,600 per year), and the Celtic Shelf (1,500 per year) (Donovan and Bjørge 1995; IUCN).
The harbour porpoise has also been hunted in many areas of its range, e.g. in Puget Sound, the Bay of Fundy, Gulf of St. Lawrence, Labrador, Newfoundland, Greenland, Iceland, Black Sea, and the Danish Belt Seas. Many of these fisheries are now closed, but hunting of harbour porpoises still occurs in Greenland. Assessments of population impacts of these takes are not currently available (IUCN).
We are currently running a Porpoise Photo-ID project which, with the help of a team of 10 PhotoID volunteers, aims to investigate areas including site fidelity, population structure and habitat use. Initially the project will focus on Strumble Head, and we then aim to expand it out and work with partner organisations to build a fuller picture of how these porpoise use the coastline.