Mass-nesting events in olive ridley sea turtles: environmental predictors of timing and size

During the mass nesting of olive ridley sea turtles, Lepidochelys olivacea, thousands of adult females aggregate offshore, then emerge from the ocean together to lay their eggs along small, specific stretches of coastline. Little is known about the mechanisms that underlie synchronization of mass nesting. As a first step towards identifying environmental variables that control or affect the timing of mass-nesting events, we analysed 10 years of nesting data from Ostional, Costa Rica, a Pacific beach where mass-nesting events occur throughout the year. The onset of mass nesting was not uniformly distributed across lunar phase, with mass nesting occurring predominantly near last-quarter moon. Statistical models were developed to investigate whether environmental variables could be used to predict the timing and size of mass-nesting events. Predictions of the onset of nesting were improved by considering lunar phase and the time since the previous mass-nesting event as well as several oceanographic variables. Predictions of the number of turtles participating in nesting events were improved by considering salinity, relative humidity and nearshore current velocity, three parameters related to weather patterns and rainfall. Overall, the results imply that mass-nesting events at Ostional tend to occur near last-quarter moon but do not follow an invariant lunar or seasonal pattern. Instead, the results suggest that physiological and environmental factors interact to influence mass-nesting events, with no single environmental variable serving as an infallible predictor of either timing or size.