Scientists are investigating the mysterious disappearance of more than 5,000 common seals from Britain’s coastline.

Zoologists from the University of St Andrews are so concerned about the catastrophic slump in population that they are carrying out the first complete survey of Scotland’s common seal population, home to 80 per cent of the British total.

Two teams of researchers will spend the next two weeks flying over the coast in helicopters using military-specification thermal imaging technology to pinpoint seals.

Flying at up to 90 knots and 700ft above the sea, they expect to cover about 55 miles of coast every hour but are limiting their flying to several hours either side of low tide - the best time to view seals. The thermal imager can detect a seal up to two miles away, showing it as a little white blob on a sand bank or rock.

The seals will be counted as they appear, but the footage will also be recorded so that the findings can be double-checked.

Both teams set out last week, one beginning at Berwick-upon-Tweed in England and working its way around the east and north Scottish coasts, the other starting in the Solway Firth and following the West Coast. They are expected to converge in the Outer Hebrides this month.

Callan Duck, senior research zoologist at the university’s sea mammal research unit, said that the slump in population was a “mystery”.

The decision to map the entire population in one go was prompted by a routine survey of Orkney and Shetland last summer showing that numbers had dropped by up to 45 per cent over the previous five years, he said. The population had crashed to 7,277, compared with 12,635 in 2001.

Mr Duck said: “We want to find out what the reasons are for that decline, and if that decline is continuing. We also want to find out if the decline is limited to the East Coast of Scotland or if it is also happening on the West Coast.”

He said: “It’s possible that seals are being shot, though if people do shoot seals the carcasses are usually found and folk haven’t been finding carcasses in great numbers. It could be disease, but again there would be carcasses.” He said that the big rise in the grey seal population may be a factor. Both species rely for food on sand eels, which have declined sharply over the past few years.

Mr Duck said that, in his view, there was no single reason for the slump in the common seal population.

Ailsa Hall, another team member, said: “It’s baffling. It could be killer whales, it could be changes in the environment, it could be pollutants in the water, it could be shooting. We just don’t know.”

There have been mounting calls in recent years for a tighter restrictions on the shooting of seals. Although in theory they are protected by a range of conservation measures, fishermen are allowed to kill seals if they believe that their fishing equipment is at risk.

Ross Flett, chairman of Orkney Seal Rescue, said: “Common seals are still being shot even though there is a big reduction in numbers. At the moment the law is a joke because fishermen can get away with whatever they want.”

There are about 30,000 common seals, or harbour seals, in Britain and about 150,000 grey seals. The sea mammal research unit expects to publish its findings next year.

Blubbery

- The common seal grows up to 7ft (2.1m) long and weighs up to 140kg (300lb)

- Its coat is grey or brownish grey and more spotty than that of the grey seal; its eyes are rounder and it has a short nose and spaniel-like face

- Becomes sexually mature at age 3 or 4 and normally lives 20-25 years

- Breeds in June/July and moults from July to September

- Eats up to 5kg of fish a day, including sand eels, cod and haddock Also known as harbour seal

Source: Times database

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