Sea cucumbers are heavily exploited worldwide, yet data are lacking on animal mobility and life-history parameters for fishery management and conservation planning. This study assessed movement and growth rates for a medium-sized holothuroid, Pearsonothuria graeffei, harvested throughout the Indo-Pacific. We used photographic mark-recapture to track long-term movements and growth for this species over 2 yr. Recapture rates were 67-72%. Movement rates averaged 9 m yr-1, and many individuals were found in aggregations and recaptured there in 2 successive years. Growth was highly variable; small animals (<700 g) tended to gain weight while large animals (>700 g) tended to lose weight. Some individuals lost weight and then regained weight, while others gained weight and later lost it. Growth models estimated that P. graeffei approach their average maximum weight (769 g) in 7-12 yr and are slow-growing (growth coefficient = 0.17). Natural mortality (M; 0.48 yr-1) was low, and estimated longevity was 18 yr. P. graeffei exhibits traits that heighten its vulnerability to overfishing: aggregation behaviour, low mobility, slow growth, a long lifespan and low M. The site fidelity and low mobility infer that a system of small reserves would effectively protect breeding populations and that emigration to new sites is very limited. This study provides the first published evidence from natural habitats that holothuroids can lose and later regain weight. Our empirical findings suggest that small- to medium-sized holothuroids might be slower growing and longer lived than previously believed, imploring a more conservative approach to conservation policy.