Individual specialization and behavioral plasticity in a long-lived marine predator

•Adult marine turtles exhibit high levels of individual specialization on habitat use.•Heterogeneity in reproductive output is strongly liked to foraging ground quality.•Stable isotope analysis allows reconstructing individual foraging trajectories.•Most females do not shift habitats as adults despite low fitness.•Adult marine turtles have a low behavioral plasticity once specialized.

Individual specialization in vertebrates is often related to morphological variability, but can also reflect a diversity of trajectories during the learning sensitive period in early life. In both cases the capacity of adults to adapt to new environments can be limited if further morphological or behavioral change is not possible. Adult loggerhead turtles Caretta caretta (Linnaeus, 1758) from Cape Verde (NW Africa) may forage in the open ocean or on the continental shelf. Oceanic foragers prevail in the population, but neritic foragers grow larger, have a higher reproductive output and produce best fitted offspring. Previous research suggests that the high prevalence of oceanic foragers is because the migratory routes followed by juvenile turtles during their early life results into a low probability of settlement on the African shelf. The stable isotope ratios of C and N in 60 μm carapace layers from 14 adult females have been analyzed to reconstruct retrospectively their individual habitat use patterns and test the hypothesis that adult loggerhead turtles remain faithful to their foraging grounds even if sub-optimal. Only two turtles exhibited clear oceanic-neritic shifts, approximately 22 and 15 years before sampling. The remaining turtles had foraged in neritic (3) or oceanic (9) habitat as long as recorded in the carapace scutes (approximately 8-37 years), despite the smaller body size and the lower reproductive output associated to oceanic foraging. These results suggest that habitat shifts during adulthood are unlikely in this species and support the hypothesis that only during the juvenile stage loggerhead turtles are flexible enough to adapt to contrasting environments.