Stable isotopes confirm a foraging dichotomy in juvenile loggerhead sea turtles

Differential habitat use and foraging behaviors at various life-stages within a population can have profound consequences for survivorship, stage duration, and time to maturity. While evidence for plasticity within a given life-stage in marine species is mounting, factors that contribute to this diversity remain poorly understood. We used stable isotope analysis of consumer and prey tissues to describe the trophic niche width of juvenile loggerhead turtles (Caretta caretta) that have been tracked and previously shown to have significant variation in movement behaviors (oceanic versus neritic). Results of a Bayesian mixing model indicated that whereas benthic invertebrates dominated the recent diet of neritic turtles (determined through blood plasma), pelagic prey items contributed substantially to the diets of oceanic turtles. Analysis of temporally protracted diet composition (determined through red blood cells) reflected contributions from pelagic prey for all turtle groups, indicating that all turtles fed in the pelagic zone during overwintering periods. These results imply that the previous satellite tracking results reflect the turtles' prior foraging habits. Our study highlights the need for an integrative management approach of North Atlantic juvenile loggerheads and validates the use of stable isotopes for determining their differential habitat use.