Watching a school of harbour porpoises feeding off the coast is an impressive sight. They roll along together, just breaking the surface with their curved, finned backs like so many Loch Ness monsters.
It is not necessary to take a boat to see them, for they usually stay close inshore, entering harbours as their name suggests, and frequenting the long stretch of coast between Strumble Head and St Davids Head in large numbers.
The viewing hide on Strumble Head, where naturalists congregate to watch migrating birds and to count passing marine mammals, is an ideal place to watch porpoises. Just offshore are deep depressions all along the coast which cause upwellings, bringing the porpoise’s favourite food of small schooling fish such as herring, capelin, squid and sprat nearer to the surface. They usually submerge for about a minute but can stay down for five minutes when feeding in deeper waters up to 200 metres, where they forage on the seabed. They can be watched from boats at very close quarters, for they are not particularly shy so long as there is very little noise and movement. At close quarters their small eyes and blunt noses are visible and their intakes of breath, like loud sighs, are audible, making the watching experience more intimate and enchanting. They were traditionally hunted for food and for blubber for lighting fuel in Sweden and Denmark, thousands of porpoises being caught there until the end of the 19th century and, on a smaller scale, during the two World Wars. But they are not now subject to commercial hunting except in Greenland where they are a food source. Their arch enemies are killer whales and white sharks in those areas where these predators exist, and bottlenose dolphins have also been known to kill them without eating them, doubtless due to competition for scarce food supplies. Killer whales have been sighted off the Pembrokeshire coast, but there have been no reported instances of porpoises being killed by them. Porpoises are the smallest of the marine mammals, measuring about six feet long and weighing just under 12-stone. They are vulnerable to some fishing techniques such as gill and tangle nets and by-catch in seabed-set gill nets is considered the main mortality factor. It is a bit of a mystery why they become entangled in nets as they have keen echolocation faculties, and fishermen have developed porpoise scarers or pingers to keep them away from their nets. Porpoises are cetaceans, members of the whale and dolphin family, and there are six different species. Their Latin name derives from the word ‘porcopiscus’ or pigfish which has variants in Dutch and Danish of ‘seaswine.’ But these descriptions seem a little unkind, as they are nothing like pigs, more like small dolphins, and their intakes of breath are more like a sigh than a grunt. They are much smaller and less exuberantly agile than their cousins the bottlenose dolphins, which are a familiar sight in Cardigan Bay.