Experts probing the so-called 'corkscrew deaths' of seals on Britain's East Coast believe the building of a huge offshore wind farm could be to blame.
The corpses of 50 seals with a clean 'corkscrew' cut running from head to tail have been washed up over the past 18 months.
A dozen of the mutilated seals were discovered off St Andrews, Fife, and in the Firth of Forth.
Now scientists investigating the riddle have linked it to the Sheringham Shoal wind farm, which is being built 12 miles off the Norfolk coast.
The probe is being carried out by the Seal Mammal Research Unit at St Andrews University, Norfolk Constabulary and the RSPCA.
The St Andrews scientists are working on the theory that boats associated with the Sheringham Shoal wind farm may explain the seal deaths.
Last December, work started in and around Wells-next-the-Sea harbour in Norfolk to build a pontoon and jetty to enable the transport of equipment and turbine parts to Sheringham Shoal.
It is about 12 miles from Blakeney Point, where 38 dead seals have been found.
Since April, when work on the wind farm started, there has been increased boat traffic between the coast and the offshore site.
The farm will comprise 88 260ft turbines capable of generating electricity for 220,000 homes.
It is thought that the seals have fallen victim to boats with ducted propellers, which have a non-rotating nozzle.
The propellers are surrounded by metal casing, which allows greater fuel efficiency for boats with heavy loads.
The injuries are thought to occur when the mammals are sucked into the propeller and ejected at the other end, causing the tell-tale deep, smooth, spiral cut.
Death is caused by massive tissue damage and loss of blood.
Dr David Thompson of the seal mammal research unit in St Andrews said: 'We don't think the deaths are being caused by wind farms per se - but there may be a link with the traffic associated with them.
'The wound looks as if the animal is being hit with something with a right-angled edge, but the animal is then rotating against that blade.
'We think it's probably a ducted propeller device.'
The seal unit was asked to probe the cause of the injuries by Environment Secretary-Richard Lochhead.
The RSPCA, National Trust and the Veterinary Laboratories Agency are cooperating in the investigation.
Mr Lochhead said he was 'hopeful' the team at St Andrews would get to the root of 'these disturbing seal mortalities'.
Scira Offshore Energy, which owns Sheringham Shoal, said: 'We take the death of seals on Blakeney Point very seriously and we support and co-operate fully with the police investigation into this matter.'