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Survival of a Risso’s dolphin calf entrapped by fishing gear debris
Reported by Sabina Airoldi
December 2000
Tethys Research Institute, Italy
We would like to report a remarkable example of the potential impact on cetaceans of floating debris such as discarded fishing gear in the International Ligurian Sea Cetacean Sanctuary.
The event took place in the western Ligurian Sea (43°42¹17N, 007°43¹94E), where the Tethys Research Institute has been conducting cetacean research since 1990.
On 26 October 2000, at 11:20 AM, a group of about 50 individuals including 8 calves was sighted 4.5 miles off the Italian coast, at a depth of about 1000m. The dolphins were travelling at 2-3 knot, with no steady directionality.
At 11:35 a calf - associated with an adult - was spotted with a fishing rope of approximately 2mm diameter around its foresection. The calf was towing about 20m of rope, which end was wrapped around a floater made of expanded polystyrene. The size of the buoy - that was recovered and measured later on, was 23x11x5cm.
Professional fishermen operating in the Ligurian Sea Cetacean Sanctuary routinely use this kind of floaters for their bottom long-line nets.
At 11:45, by means of the inflatable boat that serves as a dinghy to research vessel "Gemini Lab", we carefully approached the calf, still associated with its presumed mother, and we took some pictures and videos.
The mother-calf pair moved much slower than the rest of the group, because the calf was frequently slowing down.
At 12:10, moving at the same speed of the calf, we managed to remove the floater. However, we did not dare to cause further stress to the animal by handling the rope. Following the detachment of the floater, it was difficult to recognize the calf among all other group members. Therefore, we attempted to photograph every calf in the group in order to check if some of them were still entrapped by the rope.
At 13:00 the sea became too wavy and we were forced to stop working with the inflatable and go back to the motor-sailer. We remained with the group until 14:25, but we were unable to approach close enough to make further observations of the entangled calf.
Two days later, quite close to the position of the previous sighting
(43°38¹74N, 007°29¹38E), we met the same Risso¹s dolphin group and we had a chance to take more photographs of all group members. By studying the developed prints we could recognize the calf, associated with the mother, by a dark mark on its for-section caused by the rope. He was finally free.
Please direct any inquiry to Sabina Airoldi sabina.airoldi@iol.it
Photographs of the Risso's dolphin calf can be seen at http://www.tethys.org
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