The first reported observation of bottlenose dolphins ganging up to kill a common dolphin calf has emerged from Cardigan Bay in west Wales. Passengers and crew out on the dolphin-watching boat Dreamcatcher witnessed the rare example of “interspecific infanticide” on 18 April.
New Quay Boat Trips was running a dolphin-spotting charter for tourists with the charity Sea Watch Foundation, and its photographer and wildlife guide Sarah Michelle Wyer was able to capture stills while SWF research intern Dylan Coundley-Hughes obtained video footage of the attack.
The occupants of the boat had been observing resident Cardigan Bay bottlenoses when they noticed a larger pod starting to breach in the distance.
At first they thought that the dolphins were chasing one another, before realising that they were throwing something smaller, assumed to be a fish or harbour porpoise, out of the water as they breached and splashed around it.
“As we got closer, we realised it wasn’t a large salmon but, to all our surprise and sadness, it was a young common dolphin, which was not able to survive the attack,” reported New Quay Boat Trips.
The company emphasised that there was nothing those on the boat could or should have done to interfere with what was a natural behaviour – “hard as it was to watch”.
Common dolphins, which do not grow as big as bottlenose dolphins, are found further south around Pembrokeshire but rarely in the New Quay area, according to the company. It now wonders whether the hostility of its resident bottlenose dolphins towards the calf might explain their absence.
The remains of the dolphin calf were recovered by the boat and the UK Cetacean Strandings Investigations Programme was carrying out a post mortem examination.
Sea Watch Foundation routinely monitors the Cardigan Bay dolphins in terms of conservation status and protection. “Bottlenose dolphins, particularly the males, are known to pursue porpoises and other bottlenose calves, but not common dolphin calves – making this encounter an ‘interspecific infanticide’, the killing of infants of one species by members of another species,” stated the charity.
Also on Divernet: Malta’s dolphin park: is it a zoo or a circus?, BDMLR ready as dolphin strands in Cornwall, Mass dolphin stranding on Anglesey, BDMLR warn people not to return stranded mammals to the sea
Far from the first such example.
When I was a novice cave diver, in Aberdeen, in the early 90s, the “DolphinWatch” people at the Uni’s Zoology department reported regularly on such encounters between the “Moray Firth” pod of (IIRC) Common Dolphins and the overlapping pods of Harbour Porpoises. As I recall, one of the students did a number of autopsies on wash-ups and determined that the dolphins were a comparable hazard to the porpoises as propellor-strike.
Which is what you’d expect for carnivore species with overlapping ranges and food resources. Killing the young of the other species is efficient maintenance of your food resource. Don’t let the “smile” fool you – that’s engineered for efficient fish-catching.
FWIW, the arch-demons of the oil industry funded these researches. I assume the programmes got cut during a subsequent oilfield slump.
The article states in the final paragraph: “Bottlenose dolphins, particularly the males, are known to pursue porpoises and other bottlenose calves, but not common dolphin calves”. It also mentioned earlier on that the observers initially thought that the victim could have been a harbour porpoise, because that would not have been an unusual behaviour.