Grey seals feasting on their own kind, and not ship propellers, is the likely reason behind the mysterious deaths of 86 seals in Scottish waters over the last five years, according to new research.
Between 2009 and 2014, 86 seal carcasses in Scotland each had the same wound: a "corkscrew"-patterned cut that worked in a spiral around the seal's body.
Prior to a new report by Scotland's Sea Mammal Research Unit (SMRU), the deaths were strongly suspected to have been caused by the seals getting caught in the propellers of ships.
But late last year the SMRU researchers, in the midst of trying to further nail down the propeller theory in an Isle of May study, got a surprise when they were able to witness and record an adult male grey seal cannibalizing a young seal.
The seal was recorded attacking and killing a weaned grey seal pup, leaving behind the same corkscrew injury pattern. After being tagged and tracked, the adult male was later implicated in at least eight killings of pups in the same manner.
Six additional carcasses were also documented in the study area, although their deaths were not directly attributed to that specific adult male.
Of the newer carcasses observed during the latter part of 2014, the SMRU wrote in its report: "The wound patterns seen on the grey seal pups at the Isle of May clearly resembled those that have been recorded as corkscrew wounds on previous grey and harbour seal cases in Scotland."
The team's analysis of the 14 pups' injuries found 12 of them to be consistent with the corkscrew patterns seen in the prior cases.
"This clearly suggests that a proportion of the cases previously identified as the result of interactions with propellers were in fact due to grey seal predation," the team wrote.
Grey seals were also implicated last November in the mutilations of more than 1,000 harbor porpoises along the Dutch coastline.
The tagged adult male seal thought by the SMRU to have killed at least eight pups was said by the researchers to be headed for grey seal breeding sites in Germany, about 25 miles from Helgoland.
"This information will help to inform regulators, developers and others, enabling them to take it into account in their activities," said Scotland's Environment Secretary Richard Lochhead, in a statement. "Marine Scotland will continue to monitor our seal population for further injuries and any evidence about the causes."