As their name suggests, harbour porpoises (Phocoena phocoena) live close to the shore. But you won’t spot these shy, elusive mammals leaping high from the water like their exuberant dolphin cousins: a gentle roll of a porpoise’s dorsal fin over the surface usually suffices. Beneath the waves is where they really come to life – fast and furious on the hunt for food.

Harbour porpoises only grow up to 1.9m in length. This makes them the smallest cetacean (the order that also includes whales and dolphins) in UK and Irish waters. Dark grey on the top and light grey underneath, they’re perfectly camouflaged to avoid attention from orcas or sharks, and to surprise their own prey.  

Night or day, they’re always on the lookout for their next snack to maintain their body weight and body temperature. Harbour porpoises feed mostly on schooling fish, like herring, as well as squid and octopus. They have a high metabolism and can hunt up to 550 small fish per hour (according to a 2016 study of porpoises off the coast of Denmark), with a 90% success rate. And they use low level, rapid clicks or buzzes, a form of echolocation outside the human range of hearing, to help catch their prey. They can produce up to 500 of these buzzes per second.

While mostly present in Cardigan Bay, off the west coast of Wales, and off Scotland in the Moray Firth and the Western Isles, harbour porpoises can be spotted in many UK and Irish coastal waters. Porpoises’ coastal habitat brings them into contact with human activity and, in UK waters alone, this leads to thousands of unnecessary deaths each year. Pollution and habitat degradation, collisions with boats, accidental capture in fishing nets, and underwater man-made noise, are all a threat to these beautiful creatures.

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