Sightings of the elusive Risso's dolphin on the rise.

29th Jun 2010 A quick search through the advanced search facility on www.iwdg.ie shows a 53% increase in sightings of this large, pale dolphin species, when compared with the same period last year.

The Risso's dolphin is poorly understood in most waters within their range, which includes most oceans, except those in polar regions. This may in part be due to their shy nature and reluctance to associate with boats. But in recent weeks we have noticed a significant increase in sightings of this species from Counties, Wexford, Cork and Kerry.

Risso's dolphins may be confused with Juvenile or female killer whales, due to their large dorsal fin and bulbous head shape. But if seen in good light with the sun behind you, their very pale-white colouration combined with the extensive scarring giving them a unique "marbelled" effect, should make them easier to tell apart from other dolphins such as bottlenose, which are regularly seen in Irish waters. As always, IWDG would like to receive such reports.

Nick Massett, IWDG reports below on some interesting times he's spent in recent days with Eugene Mc Keown of Biospeheric Engineering as they carried out acoustic fieldwork on Risso's dolphins off the Blasket Islands, Co. Kerry......


16/06/10

With reports of Risso's dolphins being seen around the Blasket islands, Eugene McKeown set out with Nick Massett on his RIB in search of these unusual cetaceans. The purpose of this trip was to record their vocalisations, which have never previously been documented in Irish waters.

Out by Inishtooskert in ideal conditions a loosely spread group of 6-10 Risso's was spotted milling around. With their general aversion to boats and a relatively long dive time, getting close to and keeping track of these animals was going to be demanding. However, a point was reached approx 100 metres away from a couple of the Risso's, the engine was cut and hydrophones deployed.

Straight away the computer began to show short signature clicks in real-time and then more interestingly the longer buzzes associated with feeding. While this was playing out a number of photo ID images were obtained. Risso's lend themselves to photo ID with their extensive body scarring, which are the result of individuals interacting.

Later in the same trip another group of 12 or so animals was sighted out near An Tiaracht. Behaviour observed included spyhopping, breaching and tail-fluking. Again ID images were obtained and vocalisations recorded; a successful mission all round.

17/06/10

A group of five Risso's were observed milling just off the cliffs east of Fahan, Slea Head. Over the next 90 minutes these animals slowly made their way the two miles to Slea Head. Judging by their long dives they appeared to be foraging along the rocky seabed close to the shoreline, no more than 20 metres out. From Slea Head they then headed out to the Great Blasket.

18/06/10

Three Risso's from Slea Head in the Blasket sound.



20/06/10

Another RIB expedition with Eugene McKeown to try and support the data from the previous trip. It was only after eight hours on the water in testing conditions that finally a small group of Risso's was spotted on the south-western side of Blackhead Sound. With the sea-state now finally starting to improve more animals were beginning to appear.

Also on the water was Conor Ryan IWDG/GMIT on the north eastern side of Blackhead Sound and he too was reporting Risso's. His position over 1km away with animals of this same pod highlighted their dispersed grouping and the difficulty establishing numbers. The consensus was 15-20 or more animals.

At this point the hydrophone was playing a vital role in locating animals. Jus