Gray seals in waters off the Netherlands and United Kingdom are attacking and killing porpoises, leaving marine biologists to question the motives behind the animal killings.
The murderous gray seals utilize their sharp teeth to viciously rip harbor porpoises apart, leaving pieces of the animals to drift onto beaches around the northwestern Europe.
Samples of DNA recovered from wounded and dead porpoises revealed their killer, just as it might at a crime scene. Gray seals, once thought to be mostly harmless to porpoises, were found to be the culprits. Of 1,081 autopsies performed on the remains of harbor porpoises, 25 percent of the deaths were ruled to be caused by gray seals.
"This suggests that these individuals had been attacked. Harbor porpoises may be regarded as prey by gray seals. Indeed, chunks of nutritious blubber had been ripped away from the mutilated porpoises, mostly youngsters in excellent nutritious condition," Imares Wageningen UR reported in a press release.
Some marine biologists are postulating that seals may have first scavenged carcasses of porpoises trapped in fishing nets. After developing a taste for the meat of the marine mammal, the creatures may have started to hunt the species, for the first time. Gray seals normally eat fish, and these recent attacks are the first reports ever of widescale predation on harbor porpoises.
British researchers are warning that humans may also now be in danger from the rampaging seals. There are no known cases of people being killed by seals, but the animals have been known to bite humans before retreating.
Not every porpoise attacked by the unexpectedly vicious seals dies in the battle. Many of the animals escape the ambush, injured but alive.
Fishermen in Scotland have reported overly aggressive seals in their water over the last few years. These creatures weigh an average of 550 pounds, while harbor porpoises come in at around 55 pounds.
When three mutilated bodies of porpoises washed up on the Dutch shoreline in August, October, and December 2013, researchers examined the DNA evidence on the cadavers, determining they were killed by gray seals. This was the first time in history that genetic information of DNA recovered in washed-up bodies proved useful in determining the cause of death.
Ravaged porpoise bodies have washed up on coastal areas of Holland, France, and Belgium, and also the Assateague National Seashore in Maryland. Gray seals live in these areas.
The United Kingdom is home to one-third of the world's wild population of gray seals, with 180,000 of the creatures, 90 percent of which are found in waters off Scotland.
Study of attacks on harbor porpoises by gray seals is profiled in the Proceedings of the Royal Society of London B.
