Expanding the coastal forager paradigm: long-term pelagic habitat use by green turtles Chelonia mydas in the eastern Pacific Ocean

The East Pacific green turtle Chelonia mydas population is gradually recovering, yet much remains unknown about their long-term demographics and habitat use due to their inaccessibility for study. We present the first detailed characterization of age-at-settlement (similar to 3-5 yr), age-at-maturity (similar to 17-30 yr), and long-term resource use patterns for these turtles by combining skeletochronology with stable carbon (delta C-13) and nitrogen (delta N-15) isotope analysis of annual bone growth layers. We studied dead green turtles stranding along the Baja California Peninsula at Playa San Lazaro in Mexico, where their deaths are presumed to be a result of regional fisheries bycatch. Our stable isotope results indicate that these turtles utilize resources differently than other regional, lagoon-foraging green turtle aggregations. Based on stable isotope values from multiple years for individual turtles, we propose these green turtles are long-term pelagic foragers in the coastal shelf habitat of the Gulf of Ulloa and consume a more carnivorous diet from the epipelagic zone, likely including fishery discards, similar to a sympatric group of foraging North Pacific loggerhead turtles. Thus, green turtles use the Gulf of Ulloa as more than a transit area between benthic lagoon foraging and/or breeding locations. This unexpected and prolonged use of a pelagic foraging area could benefit the turtles by facilitating increased somatic growth, but may be of conservation concern as this area also experiences high fisheries turtle bycatch rates. Our findings expand the current paradigm of green turtle life history and habitat use by demonstrating an unexpected exploitation of habitat and prey for post-oceanic stage turtles.