Journal of the Marine Biological Association of India

Volume 54 Issue 2
Behaviour of Indo-Pacific humpback dolphin, Sousa chinensis (Osbeck) in the Ashtamudi estuary, southwest coast of India
A. Bijukumar and R. Smrithy Department of Aquatic Biology and Fisheries, University of Kerala, Thiruvananthapuram, Kerala 695581, India
This paper documents the behaviour of Indo-Pacific humpback dolphin, Sousa chinensis (Osbeck) found in the Ashtamudi estuary situated along the southwest coast of India. The major foraging strategy of the dolphins observed was beach hunting. The feeding-related behaviours noted were sudden bout towards the prey with shuttling or speedy zigzagging backwards and forwards and fish-stunning by tossing them into the air. The surface feeding was primarily on mullets. The dolphins displayed a stereotyped surfacing–breathing pattern, with the rostrum rising steeply above the water before the forehead breaks the surface. While travelling, they move in the same direction and the group members dive and surface synchronously for a longer time. The resting activity was primarily floatation in water. As part of socializing behaviour, the humpback dolphins exhibited vertical leaps, side leaps, quasi leaps and somersaults. The principal threat to dolphins in the Ashtamudi estuary is the heavy traffic of trawlers and other motorised vessels.
Humpback dolphin, group size, ethology, feeding,social life, resting behaviour.
Date : 17-10-2012