Grey Seals Guilty of Killing Porpoises in the North Sea

When experts first noticed hundreds of harbor porpoises washing ashore on beaches in the North Sea with horrible gashes and slash marks, no one predicted that cuddly grey seals would be guilty, according to a new study.

Scientists had expected some apex predator or a ship propeller was to blame, but DNA found in bite wounds points the finger at grey seals, indicating that their appetite has switched from fish to mammals. And while for the past decade this massacre has been focused on harbor porpoises (Phocoena phocoena), researchers are now warning swimmers of these cuddly killers.

"Many of the mutilated porpoises were found on Dutch shores used frequently by human bathers and surfers, and there would appear to be no a priori reason why humans may not be at risk from grey seal attacks," researchers wrote in the journal Proceedings of the Royal Society B.

A Dutch team examined 721 of 1,081 porpoises that were stranded between 2003 and 20013 along the Netherlands coastline and found that nearly one in five had been killed by seals.

"This makes predation by grey seals one of the main causes of death in harbor porpoises currently stranding in the Netherlands," they wrote.

"They probably first grab their victims with their heavily-armed [jaws] before tearing off large sections of the calorie-rich blubber," the team added.

According to The Guardian, it's not a scarcity of fish that's causing seals to become a bit more ambitious in their appetite, but simply that they "learned a new trick."

Not only is their mammal-eating surprising, but also the fact that it's not just one grey seal (Halichoerus grypus) to blame, but lots of them. Somehow these social animals - which hunt solo - got the word around that harbor porpoises were on the menu.

Now researchers are worried that this behavior will spread to other seals in northern Europe.

"We know there is exchange between 'Dutch' seals and 'English' or 'Scottish' seals, so there's ample opportunity for dispersal of this behavior," Mardisk F. Leopold, who led the research, told The Guardian.

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