Head-start (re-introduction) program of captive- reared hawksbill turtles in the Yaeyama Islands, Okinawa, Japan

Summary

The hawksbill turtle (Eretmochelys imbricata), Critically Endangered worldwide, was the subject of an experimental head-start program run from 2003 to 2010 by Japan's National Center for Stock Enhancement at its Yaeyama Station in Okinawa, testing whether turtles reared in captivity from local eggs could behave and survive like wild turtles once released into the sea. In 2005, researchers used ultrasonic telemetry to simultaneously release five head-started turtles, raised for 2.5 years to match the size range of wild turtles in the area, alongside five wild turtles captured locally as a comparison group. While two wild turtles returned to their original capture site, the head-started turtles dispersed inconsistently, with four leaving the monitoring area entirely and only one remaining nearby for about ten months; unlike wild turtles, which sheltered under coral at night, head-started turtles rested in less protected locations, suggesting higher predation risk. A head-started turtle later recaptured incidentally by a fisherman was found feeding on demosponges, a natural prey item, and had grown at a rate comparable to wild turtles over 88 days. Difficulties included the technical challenge of tracking small, wide-ranging juveniles, their lack of an established home range, and the decades-long timescale needed to confirm whether they eventually return to nest. The project rates itself partially successful, crediting confirmed feeding adaptation and comparable growth, while flagging inadequate shelter-seeking behavior and recommending pre-release training with structures for future cohorts.