Marine biologists have warned of significant and serious changes in the seas around Britain after detecting a steep and “frightening” fall in the numbers of common seals around the coast.
Common seals are one of Britain’s largest and most charismatic marine predators and the most likely to be seen by holidaymakers and sailors. But the latest surveys have revealed a dramatic decline in their numbers in Scotland’s waters and along eastern England.
In the worst affected areas, such as the Orkney islands, the numbers of common seals are falling by 10% a year, and have dropped by as much as half in the past six years. Along the Argyll coast, from Oban to the Mull of Kintyre, the numbers fell by a quarter last year.
Ian Boyd, a professor with the sea mammals research unit at St Andrew’s University, said it was as if the entire population had stopped breeding.
The cause was baffling scientists. “We just don’t know,” he said. “Our collective view is that there’s some large-scale process going on in the northern North Sea which is driving down seal numbers. We’re seeing a massive decline. It’s quite a frightening decline because these populations don’t change as quickly as that under normal circumstances.
“This is very abnormal. To give you an idea of the level of abnormality, the rates of decline are equivalent to these populations producing no offspring for five or six years.”
The steep declines mirror other crises in the marine environment. Biologists have reported plummeting sea bird populations, with falls of a third in numbers of puffins on the Farne islands off the Northumberland coast, and the Isle of May at the Firth of Forth, as well as declines in food sources for mammals and birds, such as sand eels. At the same time, warmer-water animals from plankton through to large fish are moving north.
Boyd said it was too early to say whether climate change was directly connected to the collapse of seal populations. He said his unit and other marine biologists were investigating a number of possibilities, including the theory that common seals – also known as harbour seals – were up against stiff competition from the larger, more robust grey seals for increasingly scarce food supplies.
Some studies suggested that killer whales, now hunting in larger numbers around Orkney and Shetland, were killing seals at pupping time.
People could be illegally shooting the seals in fish-farming areas and at inshore fishing grounds. But Boyd said these problems were localised and could not explain the UK-wide declines. The causes were likely to be complex.
The latest findings will be raised at a conference this month in Edinburgh run by the conservation agency Scottish Natural Heritage, which will give conservationists the chance to debate the challenges of climate change, alien species and conflicts between species, including common and grey seals.
All the main environment groups want the Scottish government to use powers under the proposed marine bill for Scotland to legally protect common seals, by abolishing the Seal Conservation Act 1970, which allows salmon farmers and the fishing industry to legally shoot seals that appear to damage their nets. Instead, seals should be a protected species under the Wildlife and Countryside Act, they say.
The Guardian has learned that the latest figures show that last year common seal numbers fell from 4,256 to 3,379 in Orkney, from 1,056 to 800 along the eastern coast of the northern Highlands, from 113 to 102 in the north-east, in Grampian, and from 6,702 to 4,732 on the west coast from Oban to the Mull of Kintyre. There was also a fall, from 445 to 215, in Fife, and by nearly half in the smaller populations around Lothian and Dumfries and Galloway.