Polymodal foraging in adult female loggerheads (Caretta caretta)

To determine whether loggerhead turtles (Caretta caretta) nesting in southeastern USA exhibit polymorphic foraging strategies, we evaluated skin samples for stable isotopes of carbon (delta C-13) and nitrogen (delta N-15) from 310 loggerheads from four locations on the east coast of Florida and epibionts from 48 loggerheads. We found a dichotomy between a depleted delta C-13 cluster and an enriched delta C-13 cluster. Epibionts from oceanic/pelagic or neritic/benthic habitats were largely consistent with this dichotomy. The bimodal distribution of delta C-13 could reflect a bimodal foraging strategy or-because of the potential for confounding among four gradients of delta C-13 in marine environments-a polymodal foraging strategy. We integrate our results with results from other stable isotope studies, satellite telemetry, and flipper tags to evaluate potential foraging strategies. Understanding foraging strategies is essential for development of management plans for this endangered species that has suffered a 43% population decline over the last decade.