Biometric data on hawksbill turtles (Eretmochelys imbricata) nesting at Cousine Island, Seychelles

Abstract

Nesting hawksbill turtles Eretmochelys imbricata and their eggs and young were studied on Cousine Island, Seychelles from 1995 to 1999. Numbers of females known to nest (tagged individuals) on Cousine was 146. An average of 75% of emerging adults were intercepted, and this rose to 81.6% in 1999. Mean carapace lengths and widths of adult females were 81.2×60.8 cm, and included some of the longest carapace lengths known for hawksbill turtles. There were poor correlations between adult weight and carapace length or width, but better correlations between adult weight and the product of carapace length and width. Width to length carapace proportions averaged 0.75. The mean weight of nesting females before their first recorded nesting on Cousine was 65.6 kg (51.2–83.0 kg). These were the first recorded weights for nesting hawksbills from the Seychelles. Individuals lose 8.5–15% of their body weight after laying three to five clutches. Mean clutch size was 176.7, and clutch sizes for any season showed great variation for some individuals. Clutch sizes tended to decrease after the main nesting month for the population but not necessarily for the individual. The largest clutch size of 264 is the largest recorded for hawksbill turtles worldwide. Turtles with longer carapaces tended to lay larger clutches than those with shorter carapaces, and heavier turtles generally laid heavier clutches than did lighter turtles. Eggs were usually (85.6%) somewhat elongate, measuring on average 36.3×35.5 mm, and weights averaged 25.5 g. Very few ‘pea’ eggs were found. The average hatchling weight was 14.5 g and the average carapace length and width were 39.2 and 30.1 mm, giving a mean ratio of carapace length to width of 0.77.