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MEPS prepress abstract   -  DOI:

Ecological drivers of the high predation of sea turtle hatchlings on the beach

Samir Martins, Luis Sierra, Edson Rodrigues, Javier Oñate-Casado, Iván Torres Galán, Leo J. Clarke, Adolfo Marco

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ABSTRACT: Synchronized emergence of offspring may represent an adaptive strategy to reduce predation risk. This strategy swamps the short-term capacity of predators to consume prey before offspring disperse, inducing a dilution effect, thus improving the individual’s chance of survival. In the case of sea turtles, this occurs during emergence and mass migration to the sea, to avoid potential predators on the beach. In this study, we evaluate the effect of group size on predation rates of loggerhead (Caretta caretta) turtle hatchlings during the crawl to the sea on Boa Vista Island, Cabo Verde. Our results show that synchronous emergence reduces ghost crabs (Ocypode cursor) predation rates. The mean estimated predation rate overall was 50.3%. Predation was highest at (~75%) in the smallest group sizes and decreased to ~25% at higher group sizes, due to the lower probability of an individual being attacked by a ghost crab. Our observations also indicate significantly higher predation rates at night (55%) than during the day (22%). No relationship between predation rates and the distance between the nest and the surf zone of the sea was identified, however, this is likely due to ghost crab’s behaviour of waiting close to the tide line for hatchlings during the night. Our results provide important information for the management and conservation of endangered sea turtle populations in areas with high density of predatory ghost crabs. Specifically, to reduce predation rates we recommend that hatchlings are released in large groups at twilight hours and in areas of low ghost crab densities.