Mother−offspring stable isotope discrimination in loggerhead sea turtles Caretta caretta

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 analy- sis 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 investi- gated mother−offspring stable isotope relationships and the potential for sampling hatchling log- gerheads 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, suggest- ing 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 val- ues 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 composi- tion from hatchling tissues and evaluate trophic relationships and foraging strategies of nesting females without sampling them.