Reproductive biology of the Hawksbill Eretmochelys imbricata at Tortuguero, Costa Rica, with notes on the ecology of the species in the caribbean

From 1955 through 1983, 246 hawksbills Eretmochelys imbricata have been tagged as they came ashore to nest at Tortuguero, Costa Rica, a beach they share with a large colony of green turtles Chelonia mydas. Nesting hawksbills average 82 cm in straight carapace length and grow at a mean rate of 0·3 cm year −1. Mean clutch size is 158 eggs; clutch size is poorly correlated with female body size. Average time from egg deposition to hatching emergence is 58·5 days. Mean emergence success ff hatchling is 58·3% in all clutches and 91·6% in clutches that produced hatchlings. The internesting interval averaged between 16 and 17 days. Site-fixity of females both within and between seasons was examined; a greater degree of site-fixity was exhibited between seasons than within. The distribution of hawksbill nesting activity at Tortuguero is spatially similar to, but temporally different from, that of the green turtle. There is increasing evidence from tag returns that the Tortuguero hawksbill may also share the feeding grounds of the Tortuguero green turtle in the Miskito Cays, Nicaragua. Notes on the movements and feeding habits of juveniles on their feeding grounds are included. Following a decline from 1956, there has been no consistent trend in the number of hawksbills nesting at Tortuguero since 1972. However, the mean carapace length of hawksbills has shown a steady decline, suggesting that the population is not demographically stable. The stability of an entire population cannot be determined from monitoring the number of nesting turtles each year.