Individual specialization and temporal consistency in resource use by adult olive ridley sea turtles (Lepidochelys olivacea)
During ontogenetic development, several types of marine vertebrates commonly switch their habitats and resources used. Stable isotopes of carbon and nitrogen in bone collagen in lines of arrested growth in humeri of adult olive ridley sea turtles (Lepidochelys olivacea) were analysed to detect habitat use and dietary shifts over time. Adult turtles from northeastern Brazil undergo a marked ontogenetic shift at approximately 17 years old, which is within the range of estimates of age at sexual maturity when individuals recruit from oceanic waters to coastal waters to breed. After this period, however, some individuals seem to inhabit continental shelf waters instead of returning to offshore areas. Young adults (12–18 years old) and older adults (19–23 years old) showed similar degrees of individual specialization based on both δ13C and δ15N values. Nonetheless, older adults displayed less variable carbon and nitrogen values over time than did young adults, suggesting consistent use of the same feeding grounds as the turtle’s age. Overall, adults form a generalist population with specialist individuals. Isotopic niches and potential prey contributions are consistent with this classification, reinforcing the high plasticity of habitat use by olive ridleys. The individual variability and variable habitats used make olive ridleys susceptible to fisheries bycatch in neritic and pelagic habitats, where shrimp trawl and pelagic longline fisheries occur, respectively. Therefore, the year-round cycle of this species indicates the need for actions to be taken in both coastal and offshore areas to reduce adult mortality and achieve effective conservation.