Sequential scute growth layers reveal developmental histories of hawksbill sea turtles

Understanding the basic life history patterns of highly migratory species is important for effective management. For sea turtles, evidence of developmental biogeography and discrete life stage residency provides key information for understanding resource use and population threats and defining conservation priorities. Resolving gaps in these knowledge areas is not straightforward, however. Inaccessible habitats, low survivorship, late maturity ages, and technology limitations all complicate monitoring individuals continuously throughout their life span. Here, we expand on previous studies and document a near-complete tissue record in the ultimate posterior marginal scutes of hawksbill sea turtle ( Eretmochelys imbricata ) carapace. Stable isotope analysis (SIA) of ventral scute surfaces reveals differences between three geographically isolated populations in the Pacific and Atlantic basins. Additionally, sequential sampling and SIA along growth line contours of sectioned scutes reveals developmental movements. Perhaps surprisingly, no clear or general patterns emerge. Bivariate isotope data (stable carbon, δ 13 C, and nitrogen δ 15 N) indicate that only one of six Central Pacific hawksbills showed a distinct ontogenetic shift. And while all three Western Pacific individuals showed evidence of ontogenetic shifts, these individuals had three unique patterns. We summarize regional stable isotope values for common hawksbill foraging items, discuss drivers of regional nitrogen structure, and make recommendations for future study.