THE common seal populations of Shetland and Orkney have suffered a catastrophic collapse in the past five years, but scientists last night admitted they were baffled as to why.
One theory under investigation is that global warming caused the unexpected 40 per cent crash in the number of common seals.
However, other factors including disease, starvation and persecution are all to be explored in a major investigation, as wildlife experts try to understand this sudden decline.
The Scottish Executive is also poised to take urgent action to protect the dwindling common seal population with a conservation order that will make it illegal to shoot them.
The alarm was raised yesterday by St Andrews University's Sea Mammal Research Unit, which carries out routine surveys of seals when they are hauled up on rocks and sand banks during summer. It also found that seal populations had fallen in the Firth of Tay.
Analysis of aerial photographs and infra-red images showed that last year seal numbers in Shetland and Orkney had fallen to 7,277 - compared to 12,635 when the previous survey was carried out in 2001.
Professor Ian Boyd, director of the Sea Mammal Research Unit, said: "In some areas it is a very rapid decline indeed. It is important that we now do further survey work to confirm these figures and find out whether this is a trend that is continuing."
Professor Boyd said it was too early to say with any accuracy what could have led to such a dramatic decline.
However, he said that it was likely disease and starvation could be ruled out. Earlier this month a study suggested that porpoises may have been adversely affected by a shortage of sand eels. Researchers examined the stomach contents of porpoises stranded off the east coast between 1992 and 2001 and found that up to one-third had died from starvation.
Professor Boyd said: "Global warming may be one small factor, among many we must consider, [that] could have caused this decline.
"The simple fact is at present we simply do not know what has caused this decline."
A Scottish Executive spokesman confirmed that it had begun consultations with the Scottish Seals Forum over a proposed conservation order which will bring in restrictions on shooting of common seals in Shetland, Orkney and the Firth of Tay.
SEALS have a mystical and ancient connection to Shetland.
They are at the heart of folklore in which they are known as "selkies".
In tales that date back centuries, selkies leave the sea to come ashore, where they cast off their skins and transform into beautiful people.
The winsome creatures so captivate lovelorn islanders that they go back into the sea with them and are never seen again. For reasons unexplained, these disappearances were said to happen only at midsummer.
Seal bones have also been found at the Jarlshof settlement, which dates back to the Iron Age.