Impact of fishing losses of males on the reproductive output of the large protogynous fish, Choerodon schoenleinii

Protogynous fishes are major components of commercial fisheries worldwide. They can compensate for fishing losses of males through socially controlled sex change. If their resiliency, however, is insufficient to compensate for male loss, their reproductive output can decline. Understanding the effects of fishing losses of males on reproductive output of stocks requires a detailed understanding of species-specific physiological constraints on sex change and gametogenesis. The potential impact of fishing losses of males on the reproductive output of the large protogynous species Choerodon schoenleinii was investigated by assessing the seasonality of male fishing pressure using market research. In addition, laboratory experiments imitating male removal from a social group through fishing were used to assess (1) whether females change sex during the spawning season, (2) the period after change that is required for an individual to become a functionally mature male, (3) whether individuals have sufficient capacity to fertilize batches of spawned eggs just after sex change, and (4) the impact of fishing losses of males on reproductive output of a social group. Following removal of males from 8 artificial social groups, only one female changed sex. The inability of most females to change sex during the spawning season and the slow rate of sex change may be closely related to the low natural mortality and long lifespan of this species. The female that changed sex showed low fertilization rates for at least 1 mo after sex change. Males are fished from stocks mainly before and during the spawning season, which will result in a large reduction in reproductive output due to male limitation and lower fertilization rates.