Egg-burying reptiles need relatively stable temperature and humidity in the substrate surrounding their eggs for successful development and hatchling emergence. Here we show that egg and hatchling mortality of leatherback turtles (Dermochelys coriacea) in northwest Costa Rica were affected by climatic variability (precipitation and air temperature) driven by the El Niño Southern Oscillation (ENSO). Drier and warmer conditions associated with El Niño increased egg and hatchling mortality. The fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) projects a warming and drying in Central America and other regions of the World, under the SRES A2 development scenario. Using projections from an ensemble of global climate models contributed to the IPCC report, we project that egg and hatchling survival will rapidly decline in the region over the next 100 years by ∼50–60%, due to warming and drying in northwestern Costa Rica, threatening the survival of leatherback turtles. Warming and drying trends may also threaten the survival of sea turtles in other areas affected by similar climate changes.

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Satellite telemetry has helped reveal migratory movements of sea turtles. We attached satellite transmitters (MK10 Pat Tags) to 10 post-nesting East Pacific green turtles Chelonia mydas from Nombre de Jesús, Costa Rica (in 2006Rica (in , 2007Rica (in and 2009) to track their movements, identify their foraging grounds, and elucidate their foraging behavior. Location data were analyzed by applying a switching state-space model to obtain daily position estimates and to differentiate between 2 behavioral modes (migrating and foraging). All post-nesting movements were along coastal routes ranging up to 1086 km from the nesting beach. Of the 10 turtles, 6 remained local residents of Costa Rica foraging in the Gulf of Papagayo (N = 2) and the Gulf of Santa Elena (N = 4). One individual moved southwards to the Gulf of Panama, and 3 other turtles migrated northwards to waters off the Gulf of Fonseca in northern Nicaragua, with one continuing its foraging movements northwards to coastal Guatemala. Home ranges during foraging varied widely among individuals, and the calculated size of feeding grounds ranged from 315 to 18 335 km 2 , the latter being the largest reported for this species. The fact that members of this nesting population inhabit coastal waters makes them vulnerable to human activities along the coasts of Central America. Our findings highlight the importance of Costa Rica and the coastal waters of Central America for the survival of the Endangered Costa Rican green turtles.

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