On the shores of Netherlands dozens of mangled harbor porpoises carcasses are being washed up on a daily basis. After a DNA test, specialists said the mammals were attacked and killed by grey seals. But this is very strange since grey seals do not usually hunt for porpoises. Grey seals mostly feed on fish, crabs, squids and, hardly ever, sea birds.
Experts performed autopsies on more than 1,000 harbor porpoises to find that about 25% of them were ferociously killed by grey seals.
Dr Mardik Leopold, biologist at the Institute for Marine Resources and Ecosystem Studies at Wageningen, in Netherlands, said that a large part of the dead harbor porpoises were victims of grey seals ruthless attacks. Dr Leopold has added that in most cases grey seals slaughter harbor porpoises by deliberate behavior, and in only a small part of the cases post mortem scavenging was involved.
So, it seems the wounds were inflicted while the porpoises were still alive. Scientists said there were two reasons for this conclusion. First, when found, the harbor porpoises had acute hemorrhages and, second, there were traces of freshly digested prey inside their stomachs showing that they had recently fed.
Researchers also believe that the figures in the massacre are much larger, since many porpoise carcasses with an open stomach or throat sank very rapidly and they remained unrecorded. Other wounded porpoises that had escaped the initial grey seal attack could also have died on a later date and also went unrecorded.
Grey seal behavior specialists say that these carnivorous animals originally scavenged the bodies of the dead harbor porpoises caught in the fishing nets. Gradually, their taste might have changed and started to hunt living porpoises as well. That’s why specialists came to the conclusion that this was an acquired behavior, not a natural one.
“Seals are very nippy underwater. Here in the south we have evidence of them catching salmon in the sea. They are quite fast and the thought is the seals moved from scavenging to attacking young porpoises,”
Ken Collins, a researcher from Ocean and Earth Science at University of Southampton said.
Specialists now warn that the same pattern in behavior could lead to grey seals attacks on humans, too. British and Dutch bathers are the highest risk group, since Britain hosts about 180.000 grey seals, a third of planetary population, with 90% nearby Scotland’s shores.
“Many of the mutilated porpoises were found on Dutch shores used frequently by human bathers and surfers and there would appear to be no reason why humans may not be at risk from grey seal attacks,”
Dr Leopold has also said.