Comparative demography of three black seabreams found in the Ryukyu Archipelago: implication for the definition of protandrous hermaphrodites

Life history traits of three commercial and recreational important black seabreams were characterized from the Ryukyu Archipelago of the Northwest Pacific. The active spawning periods were similar among three species and were determined to be between January and March, coinciding with a lower water temperature. The Okinawan yellow-fin seabream Acanthopagrus chinshira is a large-bodied species which exhibits a moderate initial growth, late female maturation, and an estimated intermediate lifespan of 15 years. The Pacific seabream Acanthopagrus pacificus is a medium-bodied species with a slow initial growth and an estimated intermediate lifespan of 20 years. The Okinawa seabream Acanthopagrus sivicolus is a large-bodied species with a rapid initial growth, early maturation, and an estimated intermediate lifespan of 15 years. The present study strongly suggested that all three species of the Okinawan populations showed protandrous hermaphroditism based on the available evidence (size and age frequencies and gonadal histology) and contributed toward the understanding of sexual systems in closely related black seabreams. Detailed age-based demography, which relates directly to productivity and recovery potential, also provided a necessary component for future management and conservation decisions: A. chinshira has a particularly high extinction risk and key approaches for the species preservation are urgently needed.