Establishment of Nonlethal Method to Estimate the Sex of Loggerhead Sea Turtle (Caretta caretta) Hatchling Individuals

Gonadal sex differentiation in the Sea turtles is determined by the temperature during the critical period of the incubation of eggs. The critical period is the send term of the incubation, when the incubation period was divided in three periods. Adult turtles can be sexed by the physical characteristics such as nails and the tails. Young adults can be sexed by using measurement of blood sex steroids and the laparoscopy. On the other hand, hatchlings are difficult to sex without histological evaluation of gonads. Gross et al. (1995) reported that the ratio of estradiol-17beta (E2) to testosterone (T) in the serum can be used for sex identification and the E2/T values more than 1.25 would be females. We have evaluated the E2/T values of hatchling individuals and precise temperature recording in the nests of the loggerhead sea turtle (Caretta caretta) at the Tojo beach, Kamogawa, Chiba, Japan without sacrificing.
     The mean temperatures in the sand and the nests during the critical period were all below 29.7C. There were 11 individuals showing higher values of E2/T ratio more than 1.25. We found that E2/T ratios showed significant positive co-relations with the mean temperatures in the nest during the critical period. We also found the blood drawing from the dorsal cervical sinus was not fatal. We can conclude that evaluation of E2/T ratios in the blood of the dorsal cervical sinus can be applied for the sexing of hatchlings of the sea turtles. Monitoring the sex ratios of hatchlings in the different places would provide important information for the evaluation of the global worming, the conservation and the management of reproduction in sea turtles.