UTRECHT, Netherlands, Nov. 26 (UPI) -- Scientists had always assumed gray seals only preyed on fish. Though there had been the odd sighting of what looked to be seals attacking porpoises, there was no conclusive corroborating physical evidence.
But new DNA analysis of a series of porpoise carcasses in the Netherlands suggests seals in the North Sea occasionally attack and kill harbor porpoises.
Dozens of mutilated harbor porpoises wash up on Dutch shores every year. between 2003 and 2013, researchers examined 1,081 of these specimens. Roughly two-thirds showed evidence of bite and claw marks, with DNA analysis confirming gray seals as the guilty party. It was the first time forensic examination of DNA collect from washed-up cadavers proved successful.
The new study takes the pressure off local fishermen, who had previously taken the brunt of the blame for the increase in dead porpoises. It turns out, hungry (or sometimes simply aggressive) seals aren't necessarily as sweet and cuddly as they were once once thought to be.
"People go on excursions to swim or dive with grey seals, unaware that these animals can be quite dangerous for human-sized animals," study co-author Lineke Begeman, a researcher at Utrecht University's Faculty of Veterinary Medicine, told Discovery News. "Most people consider them quite cute."
The research was published this week in the latest issue of Proceedings of the Royal Society B.
"This is a new behavior," lead researcher Mardisk F. Leopold told the Guardian. "They're normally fish eaters, they can eat a large fish, around half a meter. It's a switch from fish-eating to mammal-eating. I don't think it's indicative of lower fish stocks, they just learned a new trick."
