High habitat use plasticity by female olive ridley sea turtles (Lepidochelys olivacea) revealed by stable isotope analysis in multiple tissues

The marine habitat use of olive ridley sea turtles (Lepidochelys olivacea) from northeastern Brazil was analyzed via stable isotope analysis (SIA). Blood (red blood cells and serum), epidermis and scute samples from 46 nesting females were collected for SIA of carbon (delta C-13) and nitrogen (delta N-15) to infer the habitats used at distinct time windows. Such approach is possible because each tissue reflects consumer's diet at different time scales due to different tissue turnover time. Prey representative of both neritic and oceanic realms was used as endpoints. Differences in the residence time of delta C-13 and delta N-15 among samples indicated a shift from oceanic feeding grounds to neritic habitats before nesting or effects of prolonged fasting on stable isotope values. However, two individuals seemed to have used neritic feeding habitats for longer timespans before the nesting period. Stable isotope mixing models demonstrated high individual variability, suggesting the variable use of non-breeding grounds. Moreover, serum indicated that olive ridleys might feed during the nesting season, most likely opportunistically on discards from trawl fisheries. Finally, through correlations of stable isotope values among tissues, this study provides equations for the conversion and adequate comparison between values from different tissues. Therefore, the habitats used by olive ridley sea turtles from Brazil are vast, encompassing both oceanic and neritic habitats, where they encounter pelagic longline and trawl fisheries, respectively. The high individual variability in the population results in turtles experiencing distinct and variable threats during their annual cycle.