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.
Harbour Porpoise can dive for as long as six minutes.
Threat Level – Least Concern
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).
‘Gillnetting and driftnetting can be used to harvest bottom or pelagic fish.
A gillnet is a wall of netting set in a straight line, equipped with weights at the bottom and floats at the top, and is usually anchored at each end. Fish try to swim through the net and are caught when their gill covers are snagged, hence the name gillnetting. If allowed to drift freely, the method is referred to as driftnetting.’
©Monterey Fish Market, Inc. 2011 (http://www.montereyfish.com/pages/methods/oo_gillnett.html)
We are currently running a Porpoise Photo-ID project which, with the help of a team of Photo-ID volunteers, aims to investigate areas including site fidelity, population structure and habitat use. The project takes us around the North Pembrokeshire coast with sites in Fishguard Bay, including Strumble Head, Ramsey Sound and in the Havens, including Little Haven.