An oceanographic context for the foraging ecology of eastern Pacific leatherback turtles: Consequences of ENSO

We analyzed some of the primary biological and physical dynamics within the eastern Pacific leatherback turtle (Dermochelys coriacea) migration area in relation to ENSO and leatherback nesting ecology at Parque Nacional Marino Las Baulas (PNMB), Costa Rica. We used data from remote sensing to calculate resource availability via a net primary production (NPP) model, and to analyze the physical dynamics of the migration area via sea surface temperature fronts. Within the migration area, NPP north of 15°S was highly governed by interannual variability as indicated by the Multivariate ENSO Index while south of 15°S, production had a more seasonal signal. Nesting peaks of leatherbacks at PNMB were associated with cool, highly productive La Niña events and with large-scale equatorial phytoplankton blooms encompassing 110°W that were induced by iron enrichment following the termination of El Niño events. Resource availability in the northern migration area (eastern equatorial Pacific) appeared to determine the nesting response for the population at PNMB, Costa Rica. We suggest that ENSO significantly influences the nesting ecology of leatherbacks at PNMB because the majority of the population consists of pelagic foragers that strictly rely on the eastern equatorial Pacific for prey consumption prior to the nesting season. Coastal foragers may be a minority in the population because of high mortality rates associated with coastal gillnet fisheries along Central and South America.