Foraging ecology of green turtles (Chelonia mydas) in Peru: relationships with ontogeny and environmental variability

Feeding strategies in sea turtles are among the most important aspects of their life history, influencing demographic parameters such as growth, age-at-maturity, and reproductive migrations. However, studying sea turtle diet is often challenging and knowledge about foraging ecology is lacking for most populations worldwide. We studied green turtles (Chelonia mydas) at two disparate sites in Peru: La Aguada (similar to 14 degrees S), an area with upwelling conditions, and Virrila Estuary (similar to 5 degrees S) with year-round warm conditions. We conducted (1) in-water capture to assess population size structure and (2) esophageal lavages to recover diet components from turtles at both sites. Diet composition and feeding strategy were evaluated using several analytical approaches, and environmental influence on diet was assessed in relation to the Peruvian Oscillation Index. Our results indicate substantially different life stages and diets at the two study sites. Green turtles at La Aguada were mostly juveniles consuming animal matter, whereas turtles at Virrila Estuary were mainly sub-adults with a diet dominated by vegetal matter. Our results suggest a life-history-based habitat use model for green turtles in the southeastern Pacific Ocean. We propose that juvenile green turtles initially recruit to more southern neritic habitats of Peru, feed on high-caloric animal matter, then as individuals grow, they transition northwards to feed on lower-caloric, but abundant, vegetal matter. Our data provide a framework for ontogenic-based developmental migrations by green turtles in this portion of the southeastern Pacific Ocean, helping policymakers on the need to implement management strategies.