Supplemental feeding and other anthropogenic threats to green turtles (Chelonia mydas) in the Canary Islands

Highlights: • Juvenile green turtles regularly occur in coastal waters of the Canary Islands. • Fed turtles showed no increase in the consumption of macrophytes as turtles grew, remaining with animal-based omnivorous diets. • Fish hooks represent the first cause of admission of green turtles in the wildlife rescue centres, followed by skin wounds, boat strikes and other traumatisms. • Studied turtles exhibited high levels of some blood biochemical markers associated to a high consumption of protein and fat. Green turtles are found in the waters of the Canary Islands but little is known about the ecology and anthropogenic pressures that threaten them. Our results have revealed that juvenile green turtles, ranging in curve carapace length from 26.9–81.0 cm, are regularly found in the archipelago and originate from rookeries in both the eastern and western Atlantic. Photo-identification and satellite tracking showed high levels of site fidelity to coastal foraging grounds associated with seagrass meadows, but stable isotope analysis indicated animal-based omnivorous diets after settlement on the continental shelf, with no increase in the consumption of macrophytes as the turtles grew. Most turtles exhibited high levels of some blood biochemical markers associated with a high consumption of proteins and fat. In addition, we determined levels of some organic and inorganic pollutants. Supplemental feeding may also contribute to explain the high prevalence of hooking and boat strikes in the green turtles brought to wildlife rescue centers as compared with loggerhead turtles. Regulatory measures and surveillance should be urgently implemented in order to improve the status of the species in the archipelago.