First Suspected Grey Seal Killing of Common Dolphin in Wales
The first suspected incident of a grey seal killing a common dolphin has been documented in Wales. A short-beaked common dolphin was found dead, stranded on Newgale beach in Pembrokeshire in recent days. Marine investigators suggest the death may be linked to a group of grey seals active in the waters between Wales and the south-west coast of England.
Mat Westfield, Wales strandings coordinator at Marine Environmental Monitoring (MEM), noted that colleagues in north Devon had recently investigated similar cases.
"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.
Westfield explained that while grey seals are known to occasionally prey on smaller harbour porpoises in Welsh waters, there had been no prior reports involving common dolphins.
The dolphin, an adult female measuring 6ft (1.84m) in length, exhibited "corkscrew" injuries consistent with those observed in harbour porpoises attacked and killed by grey seals.
It also had bite marks on the pectoral fins and around the edges of torn blubber, which align with grey seal bite patterns.
The dolphin carcass has been sent for further examination. However, test results may take up to six months. Researchers will assess whether the dolphin had any previous injuries or illnesses that could have increased its vulnerability to attack.
'Ambush Attack'
Grey seals typically feed on fish such as sand eels, cod, and herring, as well as squid and crustaceans. Adult males can exceed 8ft (2.5m) in length and weigh over 660lb (300kg).
Dr Izzy Langley, from the Sea Mammal Research Unit at the University of St Andrews, stated that evidence is growing that grey seals prey on a broader range of marine mammals than previously recognized.
"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 added that this behaviour appears to be limited to certain individual seals rather than widespread across the population, with every recorded case involving an adult male seal.
While some have speculated that the Pembrokeshire dolphin might have been injured or unwell, making it easier for a seal to catch it, Langley noted that previous research has not found evidence that dolphins targeted in such attacks are already sick.
Researchers believe the attacks may involve ambush tactics from below, with dolphins potentially unaware of the threat.
"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," Langley explained.
Researchers have also found it challenging to understand how grey 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."
