禁捕后长江鱼类资源监测的技术指标建议

为了确定监测时长、监测网具、站位布局对禁捕后长江鱼类资源监测评估的有效性，于2021年5—7月在长江中游10个站位开展了鱼类资源捕捞监测，每个站位连续监测15 d，从日捕获量、物种记录数、渔获物群落结构等3方面着手，对监测时长、监测网具、站位布局等的设置进行探讨。结果显示，连续11 d捕捞监测所得累计日均渔获量基本达到稳定，连续15 d捕捞监测可以记录到站位近70%的鱼类种类数，所得累计鱼类群落结构基本达到稳定。网具类型、规格的使用覆盖对监测结果中鱼类种类记录数、鱼类群落结构有明显影响，网具使用量对监测结果中日均渔获量有明显影响。10个监测站位间的鱼类群落结构具有明显差异，结合监测站位间的空间距离来看，鱼类群落结构具有较高的空间异质性。研究表明，为了保障评估结果的准确性，基于原始监测数据进行相关评估之前，有必要对监测数据的充分性、有效性进行检验，网具类型、规格和使用量对监测结果的影响应予以适当考虑，各具体江段的鱼类群落结构评估应由相应具体江段的监测结果来支撑。本研究将为长江流域重点水域全面禁捕后的水生生物资源监测评估提供科学支撑。

Suggestions for the technical details of monitoring fish community in the Yangtze River after fishing-ban

The fishing-ban effects in Yangtze River are mainly indicated by the community recovery of aquatic organisms. To identify the effects, the aquatic organism community monitoring is critically needed. However, monitoring duration, monitoring tools and monitoring sites may severely impact its result. The current study aims to identify the impacts of monitoring duration, monitoring tools and monitoring sites on the results of fish communities monitoring and then provide suggestions for the technical details of monitoring fish community. Here, we used gillnets and cages to monitor the fish communities for 15 consecutive days in 10 sites in the middle reaches of Yangtze River form May to July, 2021. Then, we analyzed the catch per day, the recorded species per day and the fish community structure per day to research the impacts of monitoring duration, monitoring tools and monitoring sites on the monitoring results. The results showed that the catch of each day varied day by day and the average catch per day of accumulated 11 days monitoring results reached a relative stable status. The fish community structure result of each day varied day by day and the fish community structure showed by the accumulated 15 days monitoring results reached a relative stable status. Nearly 70% detectable fish species (estimated by species accumulation curve analysis) could be monitored by accumulated 15 days monitoring. The types and sizes of fishing tools obviously impacted the monitoring results of fish species and community structures. The fishing durations obviously impacted the monitoring results of catch per day. There were obviously spatial variations among the fish community structures in different reaches of Yangtze River. It suggested that in the middle reaches of Yangtze River, (1) the monitoring duration of 15 consecutive days was suitable for the fish stocks and community structure, (2) an adaptive tool assemblage is essential, (3) the fish community structure assessment of a definite reach should be based on the monitoring results of the definite reach, rather than a neighbor reach, (4) checking the sufficiency and efficiency of raw monitoring data was essential for assessing the fish stocks and community structures. Overall, the current study could provide scientific supports for the monitoring and evaluation of aquatic organism resources in key waters of the Yangtze River Basin after the fishing-ban.