Cetacean Diversity and Mixed-Species Associations off Southern Sri Lanka

Abstract

Sri Lanka, in the northern Indian Ocean island, has a relatively narrow continental shelf and an abundance of cetacean fauna in her waters. A few vessel surveys have produced data on cetacean occurrence off the east and west coast but no similar data exists for the south. To fill this data gap vessel-based transects were carried out in 2008/2009 off a selected segment of the south coast. A high sighting rate was recorded and nine species were documented: Balaenoptera musculus, Balaenoptera brydei, Physeter macrocephalus, Stenella longirostris, Tursiops truncates, Pseudorca crassidens, Feresa attenuata, Orcinus orca and Globicephala macrorhynchus. Significantly the first scientifically documented sighting of O. orca anywhere in Sri Lanka's waters was recorded. Additionally blue whale feeding aggregations including mother-calf pairs were documented off southern Sri Lanka in the Austral summer. Mixed species associations involving five species of cetaceans were also recorded. The coastal waters off southern Sri Lanka are therefore an important cetacean habitat with high diversity and mixing of coastal and usually pelagic species. The implications of the importance of the area for blue whales also warrants further study and more detailed studies are recommended to generate data that can inform future management and conservation decisions.