The smallest cetacean species in European waters, it reaches lengths between 1.4 and 1.9 metres.
With a dark grey back, paler sides and underneath and centrally placed triangular dorsal fin they can be seen nearly anywhere around the UK, however they are more common around South-west and western Ireland, West Wales, the west coast of Scotland and the Islands and Eastern Scotland. They also have a blunt head and lack a beak, characteristic of species such as the Bottlenose Dolphin.
Around the Hebrides they are resident and are seen throughout the year, usually singly or in small family groups of up to 5 individuals. These small animals tend not to be interested in boats and are unlikely to approach vessels, however it is possible to get good views of them as they surface. A little less playful than Dolphins they rarely if ever jump clear of the water. More likely to be seen is a series of quick surfaces followed by a longer dive. During a regular surface they roll across the surface and then disappear again. Their Gaelic name means 'Puffing Pig', in reference to the noise they make when they exhale at the surface.
In the Hebrides Sand-eels, Herring and Sprat make up the bulk of the Harbour Porpoise's diet, however they have been known to eat squid, octopus, shellfish and up to 20 different species of fish. When foraging they spend up to 6 minutes underwater.
Harbour Porpoise numbers have seen a decrease around the UK, this is mostly due to human activities. The area of the sea most used by humans overlaps with the highest Porpoise numbers and they are very vulnerable to over fishing, marine litter and getting entangled in fishing nets. At present it is thought that several thousand Porpoise may die in the UK every year due to being drowned in fishing nets. Around the Hebrides Killer Whales and Bottlenose Dolphins have both been seen to prey on Harbour Porpoise.