Using Stable Isotopes to Determine Foraging Areas of Leatherback Sea Turtles: Limitations of the Isotope Tracking Technique in the Western Atlantic Ocean

Reproductive output has long been linked to habitat quality and resource availability. Individuals foraging in high-quality habitats with high resource availability will have better body conditions and higher survival rates, as well as greater reproductive output. Post-nesting, Western Caribbean leatherback turtles are known to migrate to at least two foraging regions: the western North Atlantic and Gulf of Mexico. This study had three objectives: [1] measure δ13C and δ15N values in bulk skin tissue of females nesting in Parismina, Costa Rica to reveal prior foraging region; [2] assess influence of foraging region on female body size and reproductive output; and [3] conduct a comprehensive review of existing stable isotope data for various taxa (from baseline producers to higher order consumers) and create δ13C and δ15N isoscapes to use as a reference for the Gulf of Mexico and western North Atlantic. It was not possible to infer foraging region for skin samples collected in Parismina based on stable isotope values, nor was there a relationship between stable carbon values and reproductive output. Synthesized isoscapes from published stable isotope data showed substantial variation between taxa and sampling regions. Stable carbon values were higher in the Gulf of Mexico than the western North Atlantic for leatherbacks, but no other consistent trends were distinguishable. Although I was unable to validate it as a primary technique to study leatherback movements between nesting and foraging grounds, stable isotope analysis still holds important conservation value for leatherbacks in conjunction with satellite tracking. This study highlights the need for more stable isotope data and longer-term data collection