In Southeast Asia, virtually all knowledge about sea turtle biology is derived via nesting beach studies. This study investigated life-stage parameters for a foraging population of immature Green Turtles Chelonia mydas off the coast of Borneo, Malaysia, to elucidate a significant portion of the at-sea life-stage component. Mark–recapture provided new data on localized movements between captures, growth, and residency period. Laparoscopic examination provided information on sex ratios and maturity. Turtles moved only an average of 380 m between recaptures and exhibited site-fidelity over several recaptures spanning up to two years. Size classes suggested all animals were juveniles and ranged from 38–80 cm CCL. Growth rates among recaptures averaged 3.6 cm yr⁻¹. Laparoscopic examinations of the gonads confirmed that all individuals were immature, with a sex ratio of 1M ∶ 4F. These initial data on foraging C. mydas population structure and dynamics are of use for life-stage population models and turtle management and recovery planning.