离底拖网的游泳动物群落特征——以兄弟岛渔场为例

为探究离底拖网对游泳动物的群落结构以及捕捞量的影响,于2019年9月和2020年9月在福建海域兄弟岛渔场开展了36网次的底拖网专项试验,通过调整曳纲长度控制底拖网作业过程中的网位变动,分别保持底拖网作业在贴底或离底1 m的状态,以物种组成、渔获量对数均值、优势度、多度谱、多样性等参数,分析和比较了贴底拖和离底拖的游泳动物群落结构变化。结果显示:贴底拖和离底拖游泳动物的种类数分别为126种和79种,贴底拖游泳动物的总尾数和总体质量均为离底拖的3倍,贴底拖的渔获量对数均值比离底拖要高0.36,表明贴底拖网的渔获物以栖息于底层的游泳动物为主；贴底拖的游泳动物多样性、均匀度和丰富度分别为2.81、0.65和10.01,均高于离底拖(2.29、0.60和8.13),经济幼鱼的比例更高,说明贴底拖会对游泳动物的多样性以及幼鱼造成更大的损害；离底拖游泳动物的优势度指数为0.41,高于贴底拖的0.29,其多度谱曲线更陡,说明近底层游泳动物群落优势种分布更集中、数量分布不均匀。研究结果可以为底拖网渔业的科学管理提供依据。

Effects of bottom trawling and off-bottom trawling on community structure of nekton in Xiongdi Fishing ground

The method of bottom trawl from bottom can reduce the disturbance and physical influence of bottom trawl and protect the ecological environment of benthic organisms.In order to further research the impacts of bottom trawl operations on bottom fishery resources,special bottom trawl trials were conducted on 36 nets in September 2019 and September 2020 in the Xiongdi Fishing ground of Fujian,the changes of community structure of nekton in bottom and near bottom were analyzed and compared by using species composition,logarithmic mean of bottom trawl catch,dominance,abundance spectrum and diversity,etc.,and the effects of bottom trawling and off-bottom trawling on the community structure of nekton were revealed,which provided a basis for the scientific management of bottom trawl and the adjustment of the structure of inshore fishing.The results showed that there were 126 species of nekton in the catch of bottom trawling and 79 species of nekton in the catch of off-bottom trawling,and the total number and weight of nekton in the catch of bottom trawling were 3 times of that of in near bottom,and the logarithmic mean of bottom trawl catch was 0.36 higher than that of in the catch of off-bottom trawling,which indicated that bottom trawl catch was dominated by nekton in the bottom.The diversity,evenness and abundance of nekton in the catch of bottom trawling were 2.81,0.65 and 10.01,these values were all higher than that in the catch of off-bottom trawling(2.29,0.60 and 8.13,respectively).The catch miniaturization was more serious in the catch of bottom trawling,and the proportion of economic juvenile fish was higher in the catch of bottom trawling,which indicated the diversity and juvenile fish were more damaged by bottom trawling.The curve of abundance spectrum of nekton was steeper in the catch of off-bottom trawling,and the index of dominance was higher in the catch of off-bottom trawling(0.41),which indicated that the dominant species distribution of nekton was more concentrated and uneven in near bottom.