grey seal pup
Cannibal grey seals behind mystery corkscrew deaths, researchers say. Andreas Trepte

Cannibal seals in Scotland have been identified as the cause of almost 100 mystery pup deaths between 2009 and 2014.

Eighty-six grey seal pups were found dead on Scottish beaches with unusual corkscrew injuries, with marine experts unable to identify the cause of the deadly wounds.

Researchers from the University of St Andrews Sea Mammal Research Unit (SMRU) have now issued a preliminary report on what caused the seal deaths, with observations of cannibalism by a male off the Isle of May.

The seals were washed up with single, smooth-edged cuts spiralling around the body. It had been suggested the injuries could have been the result of the seals getting sucked into boat propellers, however, visual observations showed otherwise.

Researchers observed an adult male during daylight hours and attacks on pups were filmed through time lapse cameras.

grey seal death
Grey seal carcasses found on Scottish shores.

The researchers gave a grisly account of the death: "On 2 December 2014, an adult male grey seal was seen to approach a weaned grey seal pup on land on the Isle of May. It grabbed the pup by the scruff of the neck and dragged it over 20m to a shallow freshwater pool. The adult then climbed on top of the pup, forced its head under water and held it until its struggles subsided.

"The male seal then proceeded to bite the back of the neck and simultaneously pull back with its head while pushing away with his fore flipper ... The study male then proceeded to eat the blubber."

Observations suggest the pup would have died from severe blood loss. After finishing its meal, the male fell asleep on the carcass. Researchers retrieved the carcass and found the corkscrew wounds matched that of the other pups.

The experts now plan to take tissue samples from the wound sites to confirm their findings.