Ocean mammals on the move
The salmon from our rivers have deserted their traditional quarters off Greenland, sprat and sand-eels are relocating to more northerly waters and the seabirds which feed on them are following suit. Meanwhile, fish normally found to the south, are turning up here. Some people fear that great white sharks will visit us. Now, evidence has emerged that at least one sea mammal species is also on the move.
Common dolphins used be regarded as occasional visitors to the west coast of Scotland but, according to the Hebridean Whale and Dolphin Trust, they now turn up regularly in spring and their numbers have risen steadily over the last decade. There are twice as many sightings nowadays as there were 12 years ago. Thirty-four ‘pods’ were recorded last year. The Trust has presented the results of surveys, carried out over the last decade, to the European Cetacean Society.
As its name implies, the common dolphin is the most numerous of the small toothed whales frequenting Irish and Scottish waters. Nobody knows how many there are but this may be the most abundant large wild animal in the world.
The Pacific Ocean has at least a million common dolphins and there may be several times that number worldwide. It is not, however, the dolphin species most often seen from the land, at least off Ireland; that distinction goes to its larger ‘bottle-nosed’ cousin. The common dolphin lives along the coast but prefers slightly deeper waters. Although seen occasionally from headlands, it seldom comes very close to the shore.
The botle-nosed dolphin, of which Fungie is the most famous representative, has the largest brain, compared to its body size, of any animal apart from ourselves. The grey and white Einstein of the ocean, however, is not as glamorous as its smaller cousin. Black on top, the common dolphin sports a curvilinear ‘hour-glass’ pattern, in cream and light grey, extending from the thrush-like bill along its sides to the neat little tail. Picasso would be proud had he created such an elegant design. A big male, 2.5m long, might weigh 120kg, compared to 270kg for a 4m long bottle-nosed dolphin.
Common dolphins are lively and inquisitive. When blue and fin whales were plentiful, the dolphins followed them. Now they swim in the wake of ships and ride the bow-waves of fast-moving boats. This may seem foolhardy and dangerous but there is little risk to an animal which can swim at more than 60km per hour. The Scots Gallic name ‘leumadair’, recalling ‘léim’ in Irish, means ‘leaper’; these playful acrobats love to jump clear of the water. Such exuberance, alas, can get them into trouble. On their occasional ventures close to shore, common dolphins often become stranded; fatalities have been recorded from every maritime county of Ireland. Precocious individuals even venture into rivers. One was found dead 135km up New York’s Hudson River. Another became stranded 270km inland.
The scientific jury is out as to whether these fun-loving extroverts are genuine long-distance migrants or just free spirits that wander randomly. They travel in groups; pods of thousands are sometimes recorded. Their annual appearance off the Hebrides, however, suggests that they have a regular migratory agenda.
The experts are cautious as to the causes of the changes in dolphin behaviour of recent years. According to Dr Conor Ryan of the Trust, ‘further research is needed to explain what is happening, the extent to which this has been caused by human activity, and the implications for other cetacean species’.
The chief suspect, however, is climate change. The waters of the North Atlantic are warming at an alarming 0.5-degree Celsius per decade. Common dolphins prefer warmer waters and seldom frequent seas where the temperature is less than 10. With the ocean warming off the Hebrides, the dolphins may be following populations of fish which have moved recently to the area.
