Species Ddiversity, Seasonal Variation and Capture Method of Small cCetaceans on the West Coast of Sri Lanka

Abstract

Species diversity, seasonal variation and capture methods were examined, in small cetacean catches and offshore sightings at the fishing sites and adjacent waters of Beruwal a and Negombo, on the west coast of Sri Lanka. from May to October 1994. 325 and 263 individual specimens of 12 and 9 species of small cetaceans (Stenella longirostris, Stenella coeruleoalba; Stenella attenuata, Tursiops truncatus, Grampus griseus, Peponocephala electra, Pseudora crassidens, Feresa attenuata, Kogia breviceps, Kogia simus, Steno bredanensis, Lagenodelphis hosei) were recorded in the landings at Beruwala and Negombo respectively. Offshore sightings contained 114 and 565 individuals, of two species (Stenella longirostris, Tursiops truncatusi off Beruwala and Negombo respectively. Species diversity between sites was not significantly different for the catch but was significant for sightings, while diversity between catch and sightings at each site was significantly different. Seasonal variation was observed in peak catches but there was no clear seasonality for offshore sightings. Capture method did not differ significantly between sites indicating increased harpooning. Many species not sighted offshore were found in catches at both sites, indicating even deep sea stocks of small cetaceans are exposed to threat by fisheries. The finding that intentional harpooning is spreading both in area and extent should be noted and investigated further.