Do loggerhead turtle (Caretta caretta) eggs vary with alternative foraging tactics?

- Egg characteristics were compared between oceanic and neritic foraging loggerheads.
- No significant differences were found in egg size or components between foragers.
- Foraging tactics did not seem to affect egg or hatchling characteristics.
- Egg mass increased significantly with straight carapace length among all females.
- The values for most nutritional components significantly increased with egg mass.

Quantifying variations in the size and viability of offspring is essential to accurately evaluate fitness differences between alternative life histories. In the present study, the size and nutritional components (water, protein, lipid, carbohydrates, and ash) of loggerhead turtle (Caretta caretta) eggs were compared between small planktivores inhabiting oceanic areas (water depths > 200 m) and large benthivores inhabiting neritic areas (depths < 200 m) that sympatrically nest on Yakushima Island, Japan. We aimed to verify whether variations in the diet, which are dependent on the environment, of a large marine reptile influence egg quality. No significant differences were found in the size or component values of eggs between oceanic and neritic foragers classified based on stable isotope ratios in the yolks. The above results imply that foraging tactics adopted by loggerhead turtles do not affect the characteristics of the eggs and hatchlings. Among all 20 nesting females analyzed, egg mass increased significantly with straight carapace length, and the absolute contents for all components (except carbohydrates) significantly increased with egg mass. Interspecies and interpopulation variations in egg characteristics are discussed in relation to adaptations to local environments.