Bottlenose dolphins attack on porpoise filmed24th May 2013
The IWDG has reported on the resident Cork harbour pod of bottlenose dolphins since they first took up residence in the waters between Weaver's and Roches Point in Febuary 2006. Since then we have validated 142 sightings of this pod and noted the addition of a calf to this group and our monitoring has facilitated photo ID and biopsy sampling of this group by UCC. Interestingly, they seem to have been largely absent from mid-July 2012 until April 2013, but a recent run of sightings would suggest that the entire group of c7 animals has returned and they are back to their usual antics.
On 22nd Dec 2007, IWDG Science officer Conor Ryan observed an attack lasting over 100 minutes by this group on a solitary harbour porpoise. The interaction ended with the porpoise limp on the surface, presumably dead. This behaviour is not a new finding for this large predator, and has been documented previously at other Irish locations. A Welsh study based on post mortem examinations revealed that up to 75% of porpoises washed up dead in the Cardigan Bay Special area of Conservation, were killed by bottlenose dolphins. There are clearly good reasons why the territories of these two Annex II species should not overlap, especially when we consider that bottlenose dolphins can weigh up to 10 times as much as an adult harbour porpoise.
We probably need to be careful in using overly emotive language when interpreting this behaviour. There is always the possibility that this is just a little entertainment for the gregarious dolphins, but it's the end result that counts. Outwardly, there may be little evidence of the assault, bar a few superficial "rake marks" caused by the attacker's teeth on the victim's flanks and head (image left), but internally the blunt traumas tell a different story, as the porpoise is likely to suffer extensive broken ribs and severe internal organ damage. So it's little consolation for the porpoise that their much larger cousins were only "playing".
On 19th May IWDG received two independent sighting reports from Paul Keal & Richie Ryan. Both hinted at the possibility that an attack had been made near Trabolgan, just east of Roche's Pt. and Paul thankfully secured some video footage which clearly shows a much smaller animal being chased and tossed in the air by a bottlenose dolphins. The footage seems very reminicent of killer whales I've seen in Patagonia tossing southern fur seal pups in the air, after snatching them off Punta Norte beach.
It's little wonder that Conor titled his article in Issue 32 of IWDG Magazine .... " a killer's smile".
This video footage is courtesy of Paul Keal, www.mainsheetimages.com. It's brief and a little distant but you'll get the picture within the opening 20 seconds. The calf referred to in the dialogue is the harbour porpoise.
Pádraig Whooley, IWDG Sightings Co-ordinator