Sea turtles return home after intentional displacement from coastal foraging areas

Abstract

Vulnerable species may be removed from their normal habitat and released at a new location for conservation reasons (e.g. re-establish or augment a local population) or due to difficulty or danger in returning individuals to original sites (e.g. after captivity for research or rehabilitation). Achieving the intended conservation benefits will depend, in part, on whether or not the released animals remain at the new human-selected location. The present study tested the hypothesis that hard-shelled sea turtles along the coast of north-eastern Australia (9–28°S, 142–153°E) would not remain at new locations and would attempt to return to their original areas. We used satellite-tracking data gathered previously for different purposes over several years (1996–2014). Some turtles had been released at their capture sites, inferred to be home areas, while other turtles had been displaced (released away from their inferred home areas) for various reasons. All non-displaced turtles (n = 54) remained at their home areas for the duration of tracking. Among displaced turtles (n = 59), the large majority travelled back to their respective home areas (n = 52) or near home (n = 4). Homing turtles travelled faster and adopted straighter routes in cooler water and travelled faster by day than by night. Our results showed that displacement up to 117.4 km and captivity up to 514 days did not disrupt homing ability nor diminish fidelity to the home area. However, for homing turtles we infer energetic costs and heightened risk in unfamiliar coastal waters. Confirmed homing suggests that moving individuals away from danger might offer short-term benefit (e.g. rescue from an oil spill), but moving turtles to a new foraging area is unlikely to succeed as a long-term conservation strategy. Priority must rather be placed on protecting their original habitat.