Stable isotope relationships between mothers, eggs and hatchlings in loggerhead sea turtles Caretta caretta

Abstract

In the past two decades, stable isotope analysis (SIA) has been increasingly used to infer dietary ecology and habitat use in sea turtles. Tissue samples for SIA are often collected from adult females during a nesting event because turtles are easily accessible then. However, this sampling opportunity can be easily missed, or the female may be disturbed during the nesting event and abandon nest construction. The current research assessed the relationships of carbon and nitrogen stable isotope values between mothers, and their eggs and hatchlings of loggerhead turtles Caretta caretta to evaluate the accuracy of using eggs or hatchlings in inferring the mothers’ stable isotope values. Whole blood and epidermis from mothers (n = 5), yolk, albumen and shell in their eggs (n = 5 per female) and epidermis, whole blood, liver, muscle and residual yolks in their hatchlings (n = 5 for 3 females) were collected from loggerhead turtles in the 2012/2013 nesting season at Mon Repos sea turtle rookery (24°47′46″S; 152°26′26″E), in South East Queensland, Australia. The effect of lipid extraction on isotopic values in sampled tissues was also evaluated. Lipid extraction had a significant effect on δ13C values for egg yolk, residual yolk and liver, but also altered δ15N values for these tissues. Significant correlations were found between adult tissues and both their egg-yolk and hatchling tissues. Isotopic values of fresh egg yolk sampled straight after oviposition and residual yolk internalized by hatchlings at hatching were similar, implying that the stable isotope values of yolk remains unchanged throughout embryonic development. Stable isotope values were distinct between different tissues sampled from the same hatchling. With the caution that our results are based on a small sample size (n = 3), they support the method of sampling hatchlings, or eggs, rather than nesting females, to infer information about the feeding habits and migratory patterns of nesting turtle populations.