杭州湾北部张网对凤鲚幼鱼的损害性分析

为探究张网捕捞作业对凤鲚幼鱼的损害性,根据2017年5—10月杭州湾北部张网渔业资源调查数据,利用全长分析、幼鱼密度和质量占比等方法,对张网渔获中凤鲚幼鱼的生物学特征及幼鱼密度的变化进行了研究分析。结果表明,5—10月各月份张网渔获物中均有凤鲚幼鱼出现,6月份凤鲚幼鱼的平均全长达到最大值112.8 mm,8月份最小,仅为64.7 mm；平均体质量则是10月份最大,达4.4 g,8月份最小,仅1.7 g。5月份凤鲚幼鱼质量密度最高,达到493.1 g/kg,8月份最低,仅为70.3 g/kg；凤鲚幼鱼的数量密度则是7月份最高,为225 ind/kg,6月份最低,为63 ind/kg。渔获中凤鲚幼鱼质量占比5月份最高,为49.3%,8月份最低,仅7.0%；9月份渔获中凤鲚幼鱼数量占比最高,为21.0%,6月份最低,仅为5.3%。研究结果表明,5月和7月杭州湾北部张网对凤鲚幼鱼的损害程度最高。为保护凤鲚幼鱼资源,除调整禁渔期以外,建议组织开展张网网目尺寸试验,研究不同网目尺寸对凤鲚幼鱼释放的效果。

Damage analysis of set nets to juvenile Coilia mystus in the north of Hangzhou Bay

According to the fishing data in the north of Hangzhou Bay from May to October of 2017,the total length and body weight of juvenile Coilia mystus were analyzed to investigate their biological characteristics and density variation.The results showed that juvenile C.Mystus always appeared from May to October,the average total length reached a maximum of 112.8 mm in June while a minimum of 64.7 mm in August, and the average weight reached a maximum of 4.4 g in October while a minimum of 1.7 g in August.For weight and quantity density, the weight density of juveniles reached a maximum of 493.1 g/kg in May while a minimum of 70.3 g/kg in August,and the quantity density of juveniles reached a maximum of 225 ind/kg in July while a minimum of 63 ind/kg in June.For weight and quantity proportion, the weight proportion of juveniles reached a maximum of 49.3% in May while a minimum of 7.0% in August,and the quantity proportion reached a maximum of 21.0% in September while a minimum of 5.3% in June.In conclusion, the damage of set nets to juvenile C.Mystus in the north of Hangzhou Bay was more obvious in May and July. Except for adjusting fishing moratorium,experiment regarding the effect of mesh size on fish release is also necessary for protecting the wild resource of juvenile C.Mystus.