Cannibalism was the cause of dozens of mysterious seal deaths on the north Norfolk coast, scientists have concluded after a five-year investigation.
Marine biologists believe that it is highly likely that adult male grey seals had killed seal pups for food.
Scientists were baffled by the cause of death after 46 seals, all with unusual corkscrew-like injuries, were discovered in an eight-mile stretch, between Wells and Blakeney between March 2009 and August 2010.
All of the dead seals were found with smooth-edged cut that starts at the head and spirals around the body.
The nature of the injuries led investigators to originally believe the deaths may have been caused by seals being caught up in ducted propellers on ships working on the Sheringham Shoal Wind Farm, which was being built off the north Norfolk coast.
But Dr David Thompson, senior research scientist at the University of St Andrews, Scotland, which has been leading the investigation, said: 'Our investigations have led us to believe that it is highly likely cannibalism was the cause.
'We believe that adult grey seals were killing seal pups for food.
'The mechanical nature of the injuries led us to believe that some sort of machinery was involved.
'There were theories that the seals were caught up in blades on ships working on an offshore wind farm, but we couldn't work out why that would happen.'
The breakthrough on how the seals died was made by a student researcher at the Sea Mammal Research Unit at the University of St Andrews in December and the investigation has been concluded in the last few days.
The student saw an adult grey seal kill a pup on the Isle of May, east of Edinburgh.
The predator forced the pup under water and clamped its jaws around the scruff of its neck while locking its fore-flippers to the mid section. It pulled upwards with his jaw while pushing down with his foreflippers, tearing flesh from the carcass before feeding on the pup which was left with a corkscrew cut.
The same seal was seen to carry out other attacks in the same way and further studies showed there to be at least three seals in the North Sea killing pups in such a fashion.
Dr Thompson said over the last two years, about six seals a year have been found dead with the same injuries.
He said: 'Seal cannibalism is rare but not unheard of and our research has shown evidence of seals killing in this way back in the late 1980s.
'We can't be 100pc certain this is what happened in Norfolk but we believe it is highly likely to be the case.'
Dr Thompson said it was a 'very surprising conclusion' and one of the most unusual cases he has worked on in his 25-year career.
Wells harbour master Robert Smith said: 'People here are very passionate about seals and we took a lot of stick at the time when people thought it was the wind farm boats causing the deaths. It was harming the public perception of the wind farm industry,
'It's nice to be able to show now that this was not the case.'
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