Causes of Stranding and Mortality, and Final Disposition of Loggerhead Sea Turtles (Caretta caretta) Admitted to a Wildlife Rehabilitation Center in Gran Canaria Island, Spain (1998-2014): A Long-Term Retrospective Study

AIMS: The aims of this study were to analyze the causes of stranding of 1,860 loggerhead turtles (Caretta caretta) admitted at the Tafira Wildlife Rehabilitation Center in Gran Canaria Island, Spain, from 1998 to 2014, and to analyze the outcomes of the rehabilitation process to allow meaningful auditing of its quality. METHODS: Primary causes of morbidity were classified into seven categories: entanglement in fishing gear and/or plastics, ingestion of hooks and monofilament lines, trauma, infectious disease, crude oil, other causes, and unknown/undetermined. Final dispositions were calculated as euthanasia (E(r)), unassisted mortality (M(r)), and release (R(r)) rates. Time to death (T(d)) for euthanized and dead turtles, and length of stay for released (T(r)) turtles were evaluated. RESULTS: The most frequent causes of morbidity were entanglement in fishing gear and/or plastics (50.81%), unknown/undetermined (20.37%), and ingestion of hooks (11.88%). The final disposition of the 1,634 loggerhead turtles admitted alive were: E(r) = 3.37%, M(r) = 10.34%, and R(r) = 86.29%. E(r) was significantly higher in the trauma category (18.67%) compared to the other causes of admission. The highest M(r) was observed for turtles admitted due to trauma (30.67%). The highest R(r) was observed in the crude oil (93.87%) and entanglement (92.38%) categories. The median T(r) ranged from 12 days (unknown) to 70 days (trauma). CONCLUSIONS: This survey is the first large-scale epidemiological study on causes of stranding and mortality of Eastern Atlantic loggerheads and demonstrates that at least 71.72% of turtles stranded due to anthropogenic causes. The high R(r) (86.29%) emphasizes the importance of marine rehabilitation centers for conservation purposes. The stratified analysis by causes of admission of the three final disposition rates, and the parameters T(d) and T(r) should be included in the outcome research of the rehabilitation process of sea turtles in order to allow comparative studies between marine rehabilitation centers around the world.