Porpoises in the Shannon Estuary 20th March 2018

22nd Mar 2018

What makes for an interesting cetacean sighting record?  Take the most recent sightings feature we wrote up here on www.iwdg.ie, which was Nick Massett's account of the killer whale pair in Dingle Bay on March 5th.  There was actually nothing all that unusual about a pair of killer whales passing through the Blaskets, but it was the fact that the species was killer whales Orcinus orca, and that they were both filmed and photographed. They are a species that capture the imagination like no other. I've travelled around the world several times following them to places like British Columbia, Patagonia and yes, even the River Lee, in Cork. Every encounter with this apex predator is unforgettable.

But what of the many hundreds of sightings reported to IWDG each year of the more commonly seen species, such as the diminutive harbour porpoise Phocoena phocoena? It can be hard for porpoises to get a look in, as they are widespread in distribution in all Irish waters and can generally be seen throughout much of the year. But Tues. 20th March 2018 produced a pretty remarkable sighting of this species, and the reason that this sighting stood out, was because it was in the Inner Shannon Estuary.  We do from time to time report here on sightings of small cetaceans that venture from open water into estuaries and follow river systems inland. Only a few weeks back we had images of what was most likely a harbour porpoise from Carrick-on-Suir in land locked Co. Tipperary. This was another first.

But this porpoise sighting stood out, as this is the first ever sighting of porpoises in the Shannon estuary that have been validated by IWDG or researchers from the Shannon Dolphin Wildlife Foundation, who have been studying the resident population of 130+ bottlenose dolphins Tursiops truncatus  for over 20 years now. Given what we know today about the incidence of bottlenose dolphins attacking and killing the much smaller harbour porpoise, it is remarkable that this pair would venture into such an area. Perhaps even more surprising given that the group comprised a mother and calf pair, with the juvenile still showing signs of neo-natal folds, suggesting it was a calf. Obviously they didn't read the signage up on Loop Head about the area's designation as a Special Area of Conservation (SAC) for bottlenose dolphins. Did they lose their way, were they following prey into the estuary, or avoiding something even more menacing offshore?  We'll never know.

Sean O' Callaghan reports that on the same day ....."At least 4 bottlenose dolphins were present at Moneypoint at 11:50am  when we left them, with more off Beal, Co. Kerry at 15:00, so they were in the area at the time."  Perhaps this was a once off event, and only time will tell if porpoises start using the inner Shannon Estuary more often, how the resident bottlenose will respond. It may not end well, but it will be interesting.

Image above and sighting report courtesy of Sean O' Callaghan, Randal Counihan and Mags Daly.

Image (right): bottlenose dolphin and porpoise interaction from Cork harbour Jan. 2017 by Tadgh O' Caoimh

By Pádraig Whooley, IWDG Sightings Officer

Ps....we've just validated our 1st basking shark sighting record of 2018, from Slea Head, Kerry on Mon. 19th March 2018 by Niamh Mc Sweeney. It's always good to see the annual return of the planet's 2nd largest fish, as it's a sign that winter is passed and spring is upon us...not that you could tell by today's weather!