ESR 17:133-138 (2012)  -  DOI: https://doi.org/10.3354/esr00412

ABSTRACT: Knowledge of foraging strategies has significant implications for the conservation of endangered loggerhead sea turtles Caretta caretta. Stable isotope analysis is a useful tool in studying the ecology of marine consumers, as nitrogen and carbon isotope ratios (δ¹⁵N and δ¹³C) may reflect an organism’s patterns of diet and habitat use. However, obtaining samples for analysis from the study species can be difficult. For female loggerhead turtles, there is a limited time window in which to collect samples while the turtles are nesting. In the present study, we investigated mother−offspring stable isotope relationships and the potential for sampling hatchling loggerheads to gain information about nesting female populations. Epidermis samples were collected from 29 nesting females and 47 of their hatchlings on Wassaw Island, Georgia, USA. The δ¹⁵N and δ¹³C values of maternal and offspring tissues were compared to determine the discrimination, or difference, in isotope values. Hatchlings that were sampled after being discovered dead in the nests had significantly different discrimination values from those that were freshly dead, suggesting that decomposition affects the reliability of isotope ratios. Therefore, we suggest using fresh hatchling samples. Hatchling δ¹⁵N and δ¹³C values were significantly correlated to the isotope values of their mothers. Freshly dead hatchlings had significantly higher δ¹⁵N values and lower δ¹³C values relative to their mothers, and there was little variation among hatchlings within a nest. These discrimination factors can be applied in the future to determine maternal isotope composition from hatchling tissues and evaluate trophic relationships and foraging strategies of nesting females without sampling them.

KEY WORDS: Discrimination factor · Carbon isotopes · Nitrogen isotopes · Sea turtle · Hatchling · Decomposition · Epidermis