This paper deals with various aspects of the biology of the Green turtle Chelonia mydas of Mandapam region caught during 1971-1976. The major food items observed in the stomachs are sea grasses Halophila ovalis, Thalassia testudinum and sea weed Gelidiella acerosa. The relationships or morphometric measurements with plastron width, which is used here as standard measurement, showed linear regression with best correlations. The relationship of carapace length (straight) with other body measurements were also examined.

The plastron width-weight relationship for 316 turtles were worked out. The regression coefficients of the same for the subadults (weighing less than 71 kg), males and females were found to differ significantly. Females greatly outnumber males in all the years. Plastron length and weight frequencies for females and males were analysed.

Using annual weight frequencies for six years from 1971 to 1976, the modals were traced. The mean weights of individual age groups were converted to plastron width and a von Bertalanffy curve was fitted. The growth parameters were determined as i, oc = 92.2241cm, K = 0.2037 and /o=-0.2965 years. It is found that the highest weight increment, 18.64 kg, is in the 7th year of age and highest plastron width, 15.2 cm, in the 2nd year.