Foraging ecology of the olive ridley sea turtle (Lepidochelys olivacea) from the Mexican Central Pacific based on stable isotopes

Knowledge regarding the trophic ecology, including the feeding habits of olive ridley sea turtles (Lepidochelys olivacea), is scarce. Although few investigations have been carried out, some results are contradictory. We described several foraging aspects of this sea turtle species in the Mexican Central Pacific (MCP) using stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N). Data were analyzed by sex, size classes (adult/subadult), season (rainy/dry), and location (coastal/oceanic). Surveys were conducted during February 2012–June 2014. A total of 120 olive ridley sea turtles were captured, of which 86 were adults and 32 subadults; 40 were females and 46 males, while the sex of two adult individuals was unidentified. Descriptive statistics and Bayesian analyses of δ¹³C and δ¹⁵N values were performed. A similar isotopic niche width (δ¹⁵N) between males and females was found; while it was wider in adults compared to subadults. A wide δ¹³C range by sex (females) and by size (adults) was evidenced. Values of δ¹⁵N differed significantly, with lower values observed during rainy seasons. There were no significant differences in δ¹³C or δ¹⁵N between turtles captured in the coastal and oceanic areas. We infer that olive ridley sea turtle feeding areas occur in coastal areas due to the occurrence of upwellings that increases primary productivity; and during the rainy season, most sea turtles fed in coastal and intermediate areas, as oligotrophic characteristics resulted in turtles increasing their feeding range. The isotopic difference between olive ridley sea turtles and the items that were sampled in the region, suggests that crustaceans, cnidarians, and small pelagic fishes are potential prey of these turtles, which support the argument that these are opportunistic foragers. The present study highlights the importance of the MCP region for the ecology and conservation of olive ridley sea turtles, which seem to feed in the region.