Killer grey seals suspected of claiming first dolphin in Welsh waters

The first suspected case of a grey seal killing a common dolphin has been recorded in Wales.

The death of a short-beaked common dolphin found stranded on Newgale beach in Pembrokeshire in recent days may be linked to a group of grey seals operating in waters between Wales and the south-west coast of England, marine investigators say.

Mat Westfield, Wales strandings co-ordinator at Marine Environmental Monitoring (MEM), said colleagues in north Devon had recently investigated similar incidents.

"It's the first recorded case in Wales and because it's so close in distance to Devon we suspect that it's just a small population of grey seals that are doing this, and operating in that area," he said.

This story includes an image some people might find upsetting

Westfield said grey seals were known to occasionally prey on smaller harbour porpoises in Welsh waters, but there had not previously been a report involving common dolphins.

He added that the dolphin, a 6ft (1.84m) long adult female, had suffered "corkscrew" injuries consistent with what is seen when a harbour porpoise has been attacked and killed by grey seals.

"It had bite marks on the pectoral fins and around the edges of the torn blubber which are consistent with grey seal bite marks," he said.

The dolphin carcass has been sent for further examination, although test results could take up to six months. Researchers will investigate whether it had any previous injuries or illness which may have made it more vulnerable to attack.

Grey seals typically feed on fish such as sand eels, cod and herring, as well as squid and crustaceans. Adult males can grow to more than 8ft (2.5m) in length and weigh over 660lb (300kg).

Dr Izzy Langley, of the Sea Mammal Research Unit at the University of St Andrews, said there was growing evidence grey seals prey on a wider range of marine mammals than previously thought.

She said they knew about grey seals killing other seals, including harbour seals.

"But now there is evidence from both direct observations and also from strandings data, that it also occurs between grey seals and harbour porpoises, and common dolphins," said Langley.

She said the behaviour appeared to be limited to certain individuals rather than widespread across the population, with every recorded case involving an adult male seal.

While some people have speculated the Pembrokeshire dolphin may have been injured or unwell in order for a seal to catch it, Langley said previous research has not found evidence that dolphins targeted in such attacks are already sick.

Researchers believe the behaviour may involve ambush attacks from below, with dolphins potentially unaware of the threat.

She said the behaviour appeared to be linked solely to adult males and may have been learned.

"I would suspect that it's probably come out of adverse interactions that have then resulted in, 'oh, hang on, I've killed this animal, now I can actually feed on it'. And then that's a learnt behaviour."

Researchers have also struggled to explain how the seals are able to catch fast-moving cetaceans such as common dolphins.

"We've always found it tricky to understand how grey seals would kill a healthy dolphin or porpoise," Langley said.

"This kind of implies that it's not evolved behaviour, in the sense that porpoises and dolphins haven't learnt to be scared of grey seals, and so they're probably foraging in similar areas.

"I assume it's more like an ambush attack."