Sustainability of sex-changing fish stocks under fishing pressure: Insights from a length-based assessment in the Persian Gulf and Oman Sea

Objective This study evaluates exploitation patterns and reproductive vulnerabilities in four commercially important hermaphroditic fish species from the Persian Gulf and Oman Sea: Arabian Yellowfin Seabream Acanthopagrus arabicus, King Soldierbream Argyrops spinifer, Fourfinger Threadfin Eleutheronema tetradactylum, and Spangled Emperor Lethrinus nebulosus. Methods Using length-frequency data, we applied the length-based spawning potential ratio method alongside sex-specific indicators, including the adult-level male index (aLMI) and effective spawning stock biomass, to assess stock status in data-limited fisheries. Results The results revealed distinct exploitation dynamics: King Soldierbream exhibited a risk of growth overfishing, with 68% of individuals (juveniles and subadults) below the maturity length. In contrast, Arabian Yellowfin Seabream showed severe male depletion (aLMI = 0.06). Spawning potential ratio (SPR) values ranged from critically low (0.18 in Arabian Yellowfin Seabream) to moderate (0.54 in King Soldierbream). However, the juvenile-dominated catch of King Soldierbream highlights that SPR alone may mask recruitment risks when large spawners are scarce and sex ratios are skewed. Therefore, SPR should be interpreted alongside the proportion of immature individuals, aLMI, and effective spawning stock biomass. Conclusion The results demonstrated contrasting patterns of sex-specific depletion: In protandrous species, male biomass was the limiting factor, whereas in protogynous species, limitations varied between female and male biomass depending on the species. The consistent absence of large spawners across all species further threatens reproductive sustainability. We recommend implementing minimum size limits and slot-harvesting strategies to protect spawning biomass and ensure the sustainable management of hermaphroditic fish in the region.