The culprits behind the mysterious mutilated porpoises washed up on Dutch shores have been identified: grey seals. They hunt the porpoises for their nutritious fat.
This is the conclusion of lengthy forensic research by Imares, the NIOZ and Utrecht University. The seals’ DNA found in bite wounds was the smoking gun. There were also traces of bites and nails on the carcasses, says Mardijk Leopold, DLO researcher at Imares. When increasing numbers of mutilated porpoises were found washed up on beaches in 2006, it was first thought that the animals had got caught in fishing nets. That explanation proved untenable and research on ships’ rudders threw up no answers either. A Belgian researcher finally came up with the seal hypothesis in 2012.
Hunting porpoises is completely new behaviour in seals. It is clear now that it is a factor to be reckoned with. About one fifth of the washed-up porpoises were victims of a seal attack. This has therefore become a significant cause of death. Since both species are protected there is probably little we can do about it. ‘That is nature for you,’ says Leopold