The bodies have a smooth cut, starting at the head and spiralling around the body.
During the past two months there have been seven incidents where dead common and grey seals were found in St Andrews Bay and the Firth of Forth.
Similar incidents have also occurred in Norfolk and on the coast of Atlantic Canada.
Inspector Mike Brown, from the Norfolk Police, was quoted by Deadline
saying: “We’ve used maps of local currents and wind patterns to trace the patch of sea they must have drifted from, but there’s nothing in it.
“The obvious guess is their bodies were sliced by propellers because there’s a shipping lane nearby, but that has been there since time immemorial.
“There have been 13 post-mortems carried out, including some by specialists from Defra which have ruled out natural causes, but we don’t have a working theory.”
Professor Ian Boyd, the director of the Sea Mammal Research Unit said that the deaths come on top of a significant decline in some of the seal populations.
reported Dr John Baxter, the head of species management at Scottish Natural Heritage, saying: “All accidental deaths of seals are a matter of concern but with the significant decline in numbers of common seals on the east coast and in the Northern Isles of Scotland in recent years this additional source of moralities is particularly unwelcome.
“It is important that the cause of these injuries and the scale of the problem are identified as soon as possible.”
Richard Lochhead, Cabinet Secretary for Rural Affairs and Environment, is encouraging any member of the public who discovers a dead seal to contact the Sea Mammal Research Unit by emailing firstname.lastname@example.org
or by calling 01334 462 630.