Seal cannibalism is likely cause to mystery deaths in UK
A group of cannibal seals have said to be responsible for fatal corkscrew injuries to other seals in UK waters over the last five years.
Marine Scotland commissioned the Sea Mammal Research Unit (SMRU), based at St Andrews University, to investigate after 86 seal carcasses were found between 2009 and October 2014 in locations such as Blakeney Point, the Isle of May and St Andrews. All carcasses had very distinctive markings.
The injuries have been described as a single, smooth-edged wound starting at the head and spiralling around the body. Until now it was thought the animals had died after being caught in ships propellers because of the extremely neat edge to the wound and the fact that the spiral cuts on their skin are consistent with rotation of the propellor blade. Sharks in Greenland were also suggested as the cause of the deaths although this has been difficult to reconcile with observations.
After years of speculation, marine experts believe they have found the culprits – rogue grey seals.
In December 2014, the SMRU observed an adult male grey seal killing five young seals at a colony on the Isle of May, biting off chunks of blubber and leaving the dead seals with the distinctive spiral injuries. These injuries closely resembled those that have been previously recorded as corkscrew wounds on grey and harbour seal cases in Scotland. After being tagged, the adult male was later implicated in at least nine killings of pups in the same manner.
While seal cannibalism is rare, it is not heard of. Previous research in the late 1980s has shown evidence of seals killing this way.
Similar evidence gathered from German waters suggests this type of predatory behaviour may be more common than previously thought.
Grey seals were also implicated recently in the mutilations of harbour porpoises in the North Sea.
This new evidence does not completely rule out ship propellers, but they are certainly less likely to be a key factor. Continued research into this issue is taking place to understand fully these unusual deaths.
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