Highly feminised sex ratio estimations for the world’s third largest nesting aggregation of the loggerhead sea turtle

Abstract

Despite being a fundamental life history character, there is a paucity of population-wide, data-driven studies of primary sex ratios for any marine turtle species. The Republic of Cape Verde hosts the third largest nesting population of loggerhead turtles in the world (hosting up to 15% of global nesting by the species). Weighting for the spatial distribution of nests, we estimate that 84% female hatchlings are currently likely produced across the population, with 85% of nests laid on Boa Vista, where incubation temperatures were coolest. In future climate change scenarios (by 2100), irrespective of beach, island or sand colour, sex ratios reach over 99% female, and three islands (Fogo, Sao Nicolau, Santiago) would cease to produce males, with >90% of nests incubating at lethally high temperatures. Given that most of the population cannot move to nest on cooler islands, we highlight that temporal refugia are amongst primary means available to this population to adapt. Under Low Emissions Scenario, without phenological adaptation, there would only be an estimated 0.14% males produced across the whole population but in Mid and High Emissions Scenarios, male production may cease on most islands.