Sex Ratio and Size Range of Small Cetaceans in the Fisheries Catch on the West Coast of Sri Lanka

Abstract

This study examined the sex ratios and size range of small cetaceans caught on the west coast of Sri Lanka, in the fish landing sites of Beruwala and Negombo, where accidental entrapment and intentional harpooning occurs. Monitoring was done from May to October 1994. A total of 588 specimens of 12 species (Stenella longirostris, Stenella coeruleoalba, Stenella attenuata, Tursiops truncatus, Grampus griseus, Peponocephala electra, Pseudo rea erassidens, Feresa attenuata, Kogia brevieeps, Kogia simus, Steno bredanensis, Lagenodelphis hose i) were recorded. The proportion of sexes was significantly different between sites. In most species females were longer than males but there was no significant sexual dimorphism in any species recorded. In most commonly caught species a larger percentage were juveniles and sub-adults. The study concludes that there is a female bias in the catch at Beruwala with the avera! number of females caught being significantly higher than the number of males. A significant difference between sites in the size of males of the species Stenella longirostris and females of Tursiops truncatus indicates that more than one form (coastal and offshore) of these species may occur around Sri Lanka, similar to previous records from the eastern tropical Pacific for S. longirostris and from the north Pacific for T truncatus. A larger percentage of juveniles and sub-adults being caught indicates the possibility of an adverse impact on populations in the future due to an eventual dearth of breeding adults and diminishing replacement levels.