Sex ratio estimation of the most eastern main loggerhead sea turtle nesting site: Anamur beach, Mersin, Turkey

Abstract

The nesting activities of loggerhead turtles (Caretta caretta) at Anamur Beach, one of their main nesting grounds along the Mediterranean coast of Turkey, were investigated during the 2006 and 2007 nesting seasons. The mean sex ratios were estimated based on gonad histology of dead hatchlings and late stage embryos and were calculated as 72.1% and 79% as females for the years 2006 (n = 366) and 2007 (n = 271), respectively. The nest temperatures of two nests and sand temperatures at nest depths were also recorded by placing electronic temperature recorders into the nests. The recorded sand temperatures were lower when close to the sea and higher towards inland. The mean temperatures of two nests during the entire incubation period were 28.9 and 31.2 °C, with 8 days' difference in their incubation period. Based on mean temperature during the middle third of the incubation period, which ranged from 28.6 to 30.8 °C, the sex ratios were calculated as 49.3% and 79.9% females, respectively. These data are statistically significant when compared by t test (t = 52.34, p < 0.0001) and pair wise comparison (p < 0.0001). The sex ratios among the beach sections were also different (?2 = 16.5, df = 4, p < 0.002). The mean incubation periods of nests were slightly shorter in 2007 compared to 2006, calculated as 48.97 and 52.51 days, respectively. According to overall sex ratio, based on incubation durations, 85.2% of the hatchlings were females and the yearly estimated sex ratio was 75.6% in 2006 and 87.8% in 2007, which is roughly similar to the histological values. The spatial and temporal variations of nests and the resulting sex ratios were due to the possible effects of global warming causing changes in the nesting site preferences of adult females.