Grey seal interaction with common dolphin….a 1st for Irish waters…. March 27th 2024

Every few weeks we receive a sighting report which makes its way as an entry into my diary under the heading…. “Standout Sightings ”. On Wednesday 27th March, I added another.  The reason for its inclusion needs a little explaining, as there is nothing that unusual these days about a common dolphin sighting off the Dublin coast, but there is when it comes with images confirming an interaction between it and a grey seal.

The day started innocuously enough with a morning swim by Terry and Catherine MacMahon who noticed a commotion in the sea just below the RNLI station in Skerries, north Co. Dublin, which they knew involved a grey seal and felt the other protagonist was a harbour porpoise. They contacted a fellow swimmer who they knew was into wildlife, who turned out to be none other than Dr Ciaran O’ Keefe, former director of the National Parks and Wildlife Service (now retired).  Ciaran contacted Johnny Woodlock of the Irish Seal Sanctuary who grabbed his camera and travelled immediately to the site, where together they witnessed the event, which had by then already played out for some time.

Luckily Ciaran had brought a good pair of binoculars along and light conditions were favourable.  While Johnny managed to secure these really interesting images you see here, which confirm the two actors in this drama were an adult male Atlantic grey seal Halichoerus grypus and a common dolphin Delphinus delphis.

They watched the proceedings within 80-100 mts of the shore, during which the dolphin moved slowly. Despite the presence of other seals in the area at this time, this incident involved a single bull and the same dolphin; raising two questions.  Why was this dolphin alone, given that common dolphins are gregarious, regularly seen in pods ranging from dozens to hundreds, even more.  Also, common dolphins are a pelagic species and while they may on occasion come close to shore to forage in groups, they’d generally not do so alone, and certainly not in this area.

Having spoken at length with both observers, they were of the view that the seal displayed no “predatory intent” and while our initial reaction was that this was surely an “attack”, which is a big word, requiring a level of proof which in this case was simply not available.  Apart from a small area of exposed flesh at the tip of the dolphin’s beak, it had no obvious injuries, and there was no blood, which you’d reasonably expect if the seal’s intention was to kill and/or eat its captive.

But Ciaran’s impression was that the seal at times had a firm hold of the dolphin, which it wasn’t going to relinquish.  He writes: “… At times the seal was on top of the dolphin, but frequently the dolphin separated from the seal. It looked as though the seal was holding onto the dolphin at times, their two heads sticking out of the water close together. The dolphin sometimes splashed, as though trying to get away, but we never saw the seal bite it. Occasionally the dolphin held its tail vertically out of the water, motionless for some seconds until it went under. We watched for two hours during which they were mostly within touching distance of each other, never far apart.  They remained in a 200 metre-wide stretch of water close to the rocky shore.”

Eventually the running tide took the pair further offshore and into deeper and choppier water until they lost sight of them.  It’s a fascinating observation which we may only understand fully if over the coming days we find the body of a dead common dolphin in the waters off Skerries, but without this hard evidence, we can only speculate as to where on the behavioural spectrum this event rests. Was the dolphin an intended meal but ultimately too much of a handful, was it potential mating material, (albeit very out of season) and a small matter of its unwilling partner being a different species, or was it just a curious plaything?  We’ll leave that up to you to decide from these images.

Interestingly, just 15 miles up the coast at Clogher Head, Co. Louth in November 2021 a similar incident was observed by Andy Smith ,which we also reported on; but in this case the victim was a harbour porpoise, which was killed and partially eaten. This was the first documented case of grey seal predation on a cetacean in Irish waters.  Is it significant that along the same stretch of east coast, we now have a second incident of our largest native pinniped interacting with a small cetacean, in what we can only assume was not a mutually beneficial encounter.

There are a few interesting theories that could be worth exploring. One possibility is that this is a new “learnt behaviour” by one or more seals, and being intelligent mammals there is nothing to prevent this behaviour spreading culturally among the wider seal population, especially if they learn that mammal meat is easier to catch or more abundant that a declining fish alternative.  It could also be a response to a rapidly changing marine environment where species such as common dolphins, once rarely recorded in the eastern Irish sea are expanding their range into areas that provide new opportunities and with them, new threats!

For now, it might leave me a little more inclined if I lived in Skerries and wanted some cold water immersion to take a cold shower!

As always IWDG extend a huge thanks to our old friend Johnny Woodlock of the Irish Seal Sanctuary, and Ciaran O’ Keefe for their input into this story.  We will of course keep you updated if there are any developments on this.


By Pádraig Whooley

IWDG Sightings Officer