东海日本鲭繁殖群体生物学特征的年代际变化

利用1960–2012年间3个时间段共1054尾东海日本鲭(Scomber japonicus)繁殖群体的基础生物学数据,对其群体组成、肥满度、性比、性成熟长度等繁殖特征的年代际变化进行了研究。结果表明,随着时间的推移,东海日本鲭繁殖群体的年龄结构和优势年龄组、肥满度指数、最小和平均性成熟长度都呈现出逐渐下降的趋势。各年代的性比均符合1∶1关系(P0.05),但呈现升高的趋势。与前2个年代相比,21世纪初期有大量1龄鱼加入繁殖群体,这有助于提高繁殖群体的数量。各年代的雌雄鱼性成熟长度之间无显著性差异(P0.05),但最小和平均性成熟长度均表现为雄鱼略大于雌鱼。面对近50年来不断增强的捕捞压力,日本鲭主要采取降低性成熟年龄、提高性腺指数、增加群体中的雌性比例、提高相对繁殖力和减小卵径等自身调节机制来保持种群的延续。针对上述日本鲭繁殖群体的生物学长期变化特征,为了保持该鱼类资源的种群平衡和渔业可持续利用,文章提出了3点渔业管理建议,分别是控制中上层渔业捕捞努力量并制定渔船及网具标准、在主要产卵场设立产卵亲体保护区及在幼鱼索饵场设立特殊禁渔期、针对日本鲭渔业实施TAC管理制度。

Inter-decadal changes in biological characteristics of reproductive stocks of chub mackerel, Scomber japonicus, in the East China Sea

<i>Scomber japonicus </i>is one of the primary pelagic fish in the East China Sea and Yellow Sea and has continued to maintain a high yield in recent years. Inter-decadal changes in the reproductive biology characteristics of <i>S. japonicus </i>must be investigated to determine the cause for the continued high production under strong fishing pressure. The inter-decadal changes in reproductive stock structural characteristics, such as the fatness index, female to male ratio, and fork length at maturity, were evaluated based on data collected from 1054 <i>S. japonicus</i> samples collected during three periods from 1960 to 2012 in the East China Sea. The results show that the age structure, dominant age group, fatness index, and the minimum and mean fork length sat maturity of there productive stocks tended to decrease with time. The 2 to 7-year age and the 2 to 5-year age groups were dominant in the 1960s, where as the 1 to 4-year age and 1 to 2-year age groups were dominant in the early 21st century. Mean fork length and mean body weight decreased by 47.04 mm and 247.39 g, respectively, from the 1960s to the early 21st century, which were decreases of 13.98% and 44.17%, respectively. The fatness index decreased by 0.14, which was a decrease of 11.48%. Mean fork length at maturity in males and females decreased by 48.07 mm and 45.70 mm, respectively, which accounted for decreases of 14.30% and 13.58%, respectively. The female to male ratio was near 1: 1 (<i>P</i>>0.05), but showed an increasing trend. A large number of age-1 fish joined the reproductive stock in the early 21st century, compared with the previous two periods, which increased the number of reproductive stocks. No significant difference in fork length at maturity was detected between males and females (<i>P</i>>0.05), but minimum and mean fork lengths at maturity in males were slightly larger than those in females. <i>S. japonicus</i> has followed some self-adjusting mechanisms to maintain population continuity. For example, reduced age at maturity and increases in the gonadosomatic index and the percentage of females have improved relative fecundity and reduced egg size in face of increasing fishing pressure during the past 50 years. We propose three fishery management strategies to maintain population stability and sustain the fishery based on the long-term changes in the biological characteristics of the <i>S. japonicus</i> reproductive stocks in the East China Sea. The first is to control the pelagic fishery fishing effort and establish fishing boat and net standards. The second is to set up spawning fish reserves on the main spawning grounds. Special closed fishing periods should be implemented during larval feeding. The third strategy is to implement a total allowable catch management system for <i>S. japonicus</i>.