Incubation periods and sex ratios of green turtles: highly female biased hatchling production in the eastern Mediterranean

Marine turtles are globally endangered and subject to numerous conservation and management initiatives, yet many aspects of their life histories remai n undescribed. All populations subject to investigation have been shown to have temperature dependent sex determination, and data in a number of cases have suggested that the sex ratio of hatchling production may be highly fe male biased. To date, the green turtle Chelonia mydas has been Little studi ed in this respect. We recorded the temperature in 18 green turtle clutches laid at Alagadi Beach, Northern Cyprus using automated intra-nest recordin g devices. The temperatures experienced within these clutches ranged from 2 6.7 to 34.1 degrees C with mean temperature ranging from 29.8 to 32.5 degre es C. No regular diel thermal cycle was observed. Incubation periods at thi s site decreased as the season progressed and ranged from 43 to 60 d (n = 2 31; 1993 to 1998). In comparison to other published studies regarding tempe rature dependent sex determination in this species, these data are strongly suggestive of a highly female biased hatchling sex ratio. This hypothesis was partly confirmed utilising histological sexing of hatchlings found dead in nests (>99% female in 1998, n = 231). From these data we estimate that the pivotal incubation period for this population is greater than or equal to 56 d and the pivotal temperature as below 29.2 degrees C. Using a conser vative assumption that 100% males are produced by nests with incubation per iods greater than or equal to 56 d and 100 % females are produced by nests with shorter incubations, for the years 1993 to 1998, we estimate that at l east 86 to 96% of hatchlings produced at this site were female.