Abundance Trends and Nesting Biology of Green Turtles Chelonia mydas (Testudines: Cheloniidae) During Ten Consecutive Breeding Seasons (2012-2021) at Akyatan Beach, Turkey.

Abstract

Data obtained from long-term survey studies are valuable for assessing the population status and trends in critical populations of threatened species, like sea turtles. Akyatan Beach is one of the most important green turtle nesting beaches in the Mediterranean and has been monitored since 2006 without interruption. The beach is 22 km long and more than 100 m wide at some points, and both loggerhead and green turtles nest on the beach. However, loggerhead nesting is very limited compared to green turtles. A total of 3866 C. mydas nests were recorded over ten consecutive years at Akyatan Beach, with a mean of 387 ± 127 nests (range = 201-559). The average nesting density was 17.6 nests km^-1 (range = 9.1-25.4 nests km^-1). In the 3309 nests, a total of 355,259 eggs were counted. The overall mean clutch size was 112 ± 26.10 eggs. Of these eggs, 50.80% hatched (depredated nests included), and 78.07% of them were able to reach the sea. The overall mean hatching success was 73.07 ± 26.20%. The overall mean incubation duration was 51.4 ± 3.5 days. The clutch sizes and hatching success differed between years, and there was a significant decreasing trend in mean incubation duration over the ten years of the study. A total of 1585 green turtle nests (41.02% of nests) were totally or partially depredated by golden jackals and wild boars, while other predators depredated 20.5% of hatchlings. The nesting data obtained since 2006 showed strong annual fluctuations ranging from 170 (in 2007) to 562 (in 2006) with a slightly increasing but statistically insignificant trend (r = 0.94, p > 0.05). The main threats to the population were depredation by jackals and wild boars.