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FORAGING ECOLOGY OF NESTING GREEN, OLIVE RIDLEY, AND LEATHERBACK TURTLES FROM NORTHWEST COSTA RICA
thesisposted on 28.04.2021, 19:20 by Alison Jenele Meeth
Understanding what sea turtles are feeding on and where they are feeding is key to understand their overall biology and will aid in understanding what type of management actions are necessary in order to conserve and protect these endangered species. Here I set out to (1) examine the population-level isotopic profiles of three sea turtle species in the Eastern Tropical Pacific; (2) determine differences in their foraging strategies; (3) attempt to gain insights about their pre-nesting origins; and (4) determine whether body size would influence the isotopic values of an individual turtle.
Stable isotope analysis (δ13C and δ15N values) was conducted on tissue samples from 52 sea turtles nesting on Playa Cabuyal, Costa Rica; 28 Pacific green (Chelonia mydas), 20 olive ridley (Lepidochelys olivacea), and 4 leatherback (Dermochelys coriacea). Nine satellite transmitters were also deployed on a separate population of post-nesting Pacific green turtles from Playa Cabuyal.
Based on isotopic profiles, green turtles in the Eastern Tropical Pacific were found to be feeding at a higher trophic level when compared to green turtles in other regions and this was supported by their increased δ15N values (16 ± 0.8 ‰). Rather than shifting to herbivory as adults, green turtles foraging in the eastern Pacific are potentially remaining omnivorous. Tracking data further confirmed that green turtles are coastal migrators and are probably inhabiting areas with high δ15N values within this region. Olive ridley turtles are exhibiting similar behavior to olive ridley turtles elsewhere due to minimal variance in their isotopic profiles (δ13C = -15.1 ± 0.7 ‰, δ15N =14.2 ± 0.8 ‰) and their known nomadic behavior. Although a small sample size, leatherback turtles showed a shift in their foraging habitats suggesting they are also feeding inshore in addition to their pelagic behavior due to their increased δ13C values (-15.5 ± 0.4 ‰). Further, as body size increased in olive ridley’s, the δ15N values significantly decreased suggesting that larger turtles prefer deeper pelagic waters with less enriched N isotope concentrations. However, in order to rule out possible external factors influencing this relationship, knowing where the turtle is originating from is crucial. This project provides data for developing isoscapes in the Eastern Tropical Pacific to aid in understanding the spatial distribution of sea turtles and their foraging grounds and the impact that foraging area may have on overall biology of these species. This information can be used to prioritize high use foraging habitats and determine the most effective management practices for protecting these species and the prey and habitat on which they rely.