OUTDOOR LIVING Could bottlenose dolphins be marking territories new?

Marking territories new?


Marine Life
John Paul Tiernan

NORMAL North Atlantic order has restored itself after a most remarkable four weeks in Ireland’s recent meteorological history. It will be hard now to discern any surface goings-on between shore and horizon with wind and swell likely to run for weeks on end as they often do in January, driven to us by lows sweeping across from Newfoundland in our general direction.
These lows stopped for that extraordinarily Siberian month, blocked by a strong high pressure air-mass to our North which made for a very still Atlantic, allowing me one evening to sharply define the space between caudal fin and ocean and see through the burst of spray between dorsal fin and sky. It could be September but for the 10 degree water I thought as the three dolphins surged powerfully high out of a flat sea and all of this silhouetted by a low cloudless sunset over Renvyle.
Such acrobatic behaviour, in particular whirling vertical leaps are more noted of the smaller common dolphin, which are usually found far offshore over the continental shelf in great numbers. They are only occasionally seen inshore and that’s usually in the southwest of the country. There was not enough light to be sure but these were most likely bottlenoses, which do from time to time leap and spin like this, and bow ride and surf of course too. But then the bottlenoses are continuously surprising us. Reports of porpoises with great shark-like chunks taken from them a hundred miles or so south of here this summer led to the surprising discovery of research, mostly from Britain, on violent bottlenose attacks on porpoises.
Where the two species occur together, the most common cause of washed up porpoises’ deaths was attacks from bottlenose dolphins according to The British Environment Ministry. They don’t compete for food and scientists are guessing that it is a simple territorial aggression, with serious costs for the muc mhara (the porpoise is the pig of the sea in Irish). Recorded damage to porpoises includes broken ribs, internal organ rupture as well as bite marks. Have some of the many that wash up on Mayo’s shores experienced the same underwater violence? Probably, but data and studies could say for sure.
The bottlenose is not the indifferent play seeker we may have thought and neither does the muc mhara dip from cuain to cuainín in Clew Bay as carefree as it could appear.

Bottlenose dolphins
THE bottlenose dolphin (Tursiops truncatus) is grey to black above and light grey on the underside. They have a tall fin and a long, rounded beak with a curved mouth-line giving the familiar smiling expression. They are usually seen in small groups and frequently inshore where they are engaging and playful. The common dolphin (Delphinus delphis) is smaller than the bottlenose with a distinctive ‘hourglass’ colour pattern on its sides; yellow to the front and light grey to the back. Above this hourglass shape is black and below is white. They have a tall fin and a long black beak. They are more commonly seen in deeper waters in large numbers, but are sometimes seen off coastal headlands in summer. Report your dolphin sightings to The irish Whale and Dolphin Group at www.iwdg.ie