浙江南部近海小黄鱼生长、死亡和单位补充量渔获量

Growth, mortality and yield per recruitment of small yellow croaker in offshore waters of southern Zhejiang

浙江南部近海是东海种群小黄鱼(Larimichthys polyactis)的重要繁殖和育肥场所。根据2016年2月、5月、8月和11月采集的2023尾浙江南部近海小黄鱼全长、体长和体重等生物学信息,利用体长频率分布估算小黄鱼种群生长、死亡参数,并利用Beverton-Holt动态综合模型评估探讨单位补充量渔获量在不同自然死亡系数和渔具选择下随捕捞死亡系数的变化趋势。研究结果表明小黄鱼von Bertalanffy生长参数为渐近体长L∞=22.58 cm,生长速率K=0.78/a,初始年龄ta=?0.37 a;自然死亡系数M值为1.343,总死亡系数Z值为4.432,捕捞死亡系数F为3.089,开发率E为0.697,表明资源处于过度开发状态;小黄鱼的首次捕捞体长L50=13.11 cm,对应首次捕捞平均年龄tc=0.743 a,小于临界年龄(0.886 a)和体重生长的拐点年龄(0.979 a),渔业主要捕捞对象为幼鱼和补充群体,无法保证资源的有效补充;根据B-H动态模型,当前的YPR值为15.279 g/ind,若降低捕捞强度到1.685,对应YPRmax为17.061 g/ind,与当前产量相比增幅11.66%;若提高开捕体长(13.11 cm→16.0 cm),YPRcur会出现显著提高(15.279 g/ind→18.766 g/ind),增幅达22.82%,表明提高开捕体长要优于降低捕捞强度。当前东海小黄鱼群系处于小型低龄化和过度开发状态,建议将小黄鱼的开捕体长提高为15 cm,保证小黄鱼的产卵亲体量及资源的可持续发展。

The offshore water of southern Zhejiang is an important breeding and fattening ground for small yellow croaker Larimichthys polyactis.In this study,based on bottom trawl surveys,2023 samples of small yellow croaker with a body length of 3.0–21.5 cm were collected in February,May,August,and November 2016 in the offshore water of southern Zhejiang.Based on the length and weight data of these samples,the dominant body length was 11.0–15.0 cm,accounting for 69.9%of samples,and the dominant weight was 20.0–50.0 g,accounting for 68.26%of samples.The age ranged from 0 to 4+years.Based on 2019 sample data,the length-weight relationship was fitted by a power function,which could be described as W=0.0217L2.8635.The power exponent b was 2.8635,meaning that L.polyactis presented a negative allometric growth pattern.The Von Bertalanffy growth parameters were estimated using FiSAT II electronic length frequency analysis I.The asymptotic length L∞was equal to 22.58,and the age at zero length(ta)was estimated as–0.37 a.The growth coefficient K was 0.78 per year,indicating the fast growth rate of this small demersal species in the offshore water of southern Zhejiang.The total mortality coefficient Z was calculated using a length-converted catch curve as 4.432,and the natural mortality coefficient M was estimated as 1.343 by the Pauly empirical formula.Therefore,fishing mortality coefficient F was 3.089,and the current exploitation rate E equaled 0.697,demonstrating that the stock was subjected to overfishing.The catch curve also determined that the current first capture L50 was 13.11 cm,corresponding to an age of 0.743,which was lower than both the critical age(0.886)and the turning point age(0.931);this indicates that the main fishing objectives were juvenile and included the recruitment group of small yellow croaker.The Beverton-Holt(B-H)model was used to evaluate the yield per recruitment for L.polyactis.Based on the dynamic B-H model,the current yield per recruitment(YPR)value was 15.279 g/ind.If F was reduced to 1.685(Fmax),the corresponding YPR was 17.061 g/ind,with an increase of 11.66%over the current YPR.When L50 was increased from 13.11 cm to 17 cm,the estimates for YPRmax would increase from 15.279 g/ind to 18.766 g/ind,an increase of 22.82%over the current YPR.Thus,it would be better to increase L50 than to reduce F.In conclusion,these data indicate that the current stock of L.polyactis is over-exploited;hence,to protect the spawning stock and maintain the population in a sustainable manner,we suggest increasing the length of the first capture L50 to 15 cm,which will satisfy full growth and correspond to the optimal yield area of L.polyactis under the present fishing pressure.