浙江南部海域银姑鱼的生活史参数估算及资源评价

为了评估银姑鱼资源开发状态，实验根据2016年在浙江南部海域底拖网的调查数据，研究了银姑鱼的生活史参数，并基于单位补充量模型对其资源状态进行评价，进而探讨不同自然死亡系数和捕捞选择性对资源评价结果的影响。结果显示，银姑鱼渐近体长估计值为25.36 cm，生长速率为0.32/年，当前开捕体长(13.52 cm)远小于其初次性成熟体长(17.79 cm)；自然死亡系数估计值为0.74，总死亡系数为2.62，当前捕捞死亡系数为1.88。基于以上参数，构建了单位补充量渔获量YPR模型和单位补充量亲体生物量SSBR模型，随着F的增加，YPR先增大后减小，而SSBR则减少。银姑鱼生物学参考点F_0.1为0.78，F_max为3.43，F_20%为0.66，F_40%为0.33，可知当前捕捞强度远大于防止补充型过度捕捞警戒线F_20%。敏感性分析结果显示，自然死亡系数的不确定性将明显影响单位补充量模型的研究结果和相关生物学参考点的估算值，而不同选择性系数，尤其是开捕体长，也直接影响单位补充量模型的结果。研究表明，当前浙江南部近海银姑鱼种群已处于补充型过度捕捞状态，为维持渔业资源的可持续发展，建议适当减小开发力度，增大开捕体长；为提高资源状态评价的准确性，建议减小自然死亡系数的不确定性。本研究可为银姑鱼资源的养护和管理提供科学建议。

Estimations of life history parameters and stock assessment for silver croaker (Pennahia argentata) in offshore waters of southern Zhejiang

While silver croaker (Pennahia argentata) is an economically and ecologically important species in the East China Sea, researches on its life history traits, stock assessment and fishery management are limited in recent years. Given the increasing fishing intensity and great changes of ecosystem, limited studies of P. argentata would lead to misunderstanding of its stock status and difficulties in its conservation and management. Based on samples from the scientific survey in the offshore waters of southern Zhejiang in 2016, this study intends to understand the life history of P. argentata (growth, maturity, and mortality), to evaluate the stock status and to provide management advice. This study analyzed the life history traits based on the widely used and empirical methods, i.e. von Bertalanffy growth function for growth parameters, logistic maturity curve, and Pauly empirical formula for mortality coefficients. The yield per recruitment (YPR) and spawning stock biomass per recruitment (SSBR) models were constructed, considering the influence of natural mortality and selectivity. The asymptotic length of P. argentata was estimated to be 25.36 cm, and the exponential rate was 0.32 in the growth function. The current length of 50% selectivity (13.52 cm) was much smaller than the length of first sexual maturity (17.79 cm). Based on the length-converted catch curve, the total mortality of P. argentata was estimated to be 2.62. The Pauly empirical formula estimated the natural mortality M to be 0.74, while the fishing mortality estimate was 1.88. Results of YPR and SSBR models revealed that the biological reference points F_max and F_0.1 were 3.43 and 0.78, while F_20% and F_40% were estimated to be 0.66 and 0.33, respectively. The current fishing intensity was much higher than F_20%, indicating recruitment overfishing for this stock. Scenarios considering different natural mortality (M=0.54, 0.64, 0.74, 0.84 and 0.94) and different selectivity (age of 50% selectivity: t₅₀=1.47,1.77, 2.07, 2.37 and 2.67), were evaluated in the sensitivity analysis for YPR and SSBR models. When M increased from 0.54 to 0.94, the estimates for the current YPR would decrease from 17.69 to 10.48, and the current SSBR would slightly decrease from 0.82 to 0.57. When the t₅₀ increased, both YPR and SSBR declined in different degrees. Both YPR and SSBR, including the biological reference points, were sensitive to M and selectivity. The stock of P. argentata. in offshore waters of southern Zhejiang has been recruitment overfished in 2016, and both natural mortality and selectivity have substantial influence on the stock assessment and management advices for this fishery. Therefore, it is recommended to reduce the fishing intensity and increase the first capture length in order to improve the conservation and management of P. argentata.