Sex ratio of the mature male and female dugongs was about 1:1 and that of younger size groups was 0.6: 1.0. The size distribution varies from year to year. The size groups 150-199 cm were dominant in all the years except during 1972. March, August and October were the months when most of the dugongs got entangled in the nets. Dugongs are found fairly in good numbers around the Islands Valai thivu and Musal thivu in the Gulf of Mannar and Devipattanam and Tondi in Palk Bay. Gulf of Mannar accounted for 76% of the dugongs. Large size dugongs were more common in Tondi (Palk Bay).