Assessment of the population status of Tachysurus sinensis in the waters near Naozhou Island based on LB-SPR and LBB models

Tachysurus sinensis is an important demersal fish species inhabiting the coastal waters near Naozhou Island, playing a key role in maintaining energy flow and ecosystem functioning within the sea. This study assessed the resource status and fishing pressure of the T. sinensis population in the waters near Naozhou Island, providing scientific evidence for fisheries resource management and sustainable development in the region. In order to assess the population status and fishing risks under limited data conditions, this study utilized length-frequency and biological sample data (n=2 614) obtained from bottom trawl surveys conducted in the waters near Naozhou Island from 2016 to 2023. Two models, the Length-Based Spawning Potential Ratio (LB-SPR) and the Length-Based Bayesian Biomass Assessment Model (LBB), were employed to comprehensively evaluate the reproductive potential, fishing pressure, and resource status of T. sinensis. The estimated von Bertalanffy growth parameter the asymptotic length (L_∞) was 344.40 mm. The LB-SPR model estimated an average fishing-to-natural mortality ratio (F/M) of 5.60 and a spawning potential ratio (SPR) of 0.02~0.03, significantly lower than the conventional threshold reference point of 0.20 and the management target of 0.40, indicating a substantial decline in the reproductive potential of the population. The LBB model further indicates that the biomass ratio (B/B_MSY) remained below 0.50 for most years, and the length at first capture (L_c) is much smaller than the optimal length (L_opt=238.43 mm), suggesting that indicating that the fishery selectively harvests immature individuals. The T. sinensis population in the waters near Naozhou Island is in a state of overfishing, facing the dual issues of growth overfishing and declining reproductive potential. The results suggest the coexistence of growth overfishing and declining reproductive potential. To achieve sustainable utilization of the stock, management measures should focus on improving fishing gear selectivity and increasing the minimum capture size. Efforts should be made to increase L_c50 to gradually approach or exceed L_m50, and fishing control rules should be established based on SPR reference points. Additionally, the protection of juvenile fish and spawning habitats should be strengthened. This study provides a scientific reference for the assessment and management of demersal fish resources under data-limited conditions.