Changes of natural reproduction of fish producing drifting eggs in downstream Shashi section, middle reaches of Yangtze River during the ten-year (2011-2020) ecological operation of Three Gorges Reservoir

2011—2020年,三峡水库共开展了14次促进坝下江段四大家鱼自然繁殖的生态调度试验,于每年5—7月在长江中游沙市江段开展鱼类早期资源调查研究,旨在掌握生态调度实施以来产漂流性卵鱼类自然繁殖的响应变化,评估生态调度对长江中游鱼类自然繁殖的贡献。十年间共采集到鱼卵35种,其中典型产漂流性卵鱼类有25种,主要种类包括贝氏(Hemiculter bleekeri)、鯿(Parabramis pekinensis)、银鮈(Squalidus argentatus)、草鱼(Ctenopharyngodon idellus)、鲢(Hypophthalmichthys molitrix)、翘嘴鲌(Culter alburnus)和花斑副沙鳅(Parabotia fasciata);鱼卵群落多样性指数H、均匀度指数E和稳定性指数ICV在年际间呈现先降低后升高的变化趋势,优势度指数D恰好相反,变化拐点出现在2017年,表明2017年以来群落多样性趋于增加,群落结构趋于稳定;产漂流性卵鱼类繁殖规模总体呈先减少后增加变化,有8个类群的繁殖规模逐年增加,鱼类繁殖高峰频次逐渐升高,大规模繁殖出现的时段逐渐延长,表明鱼类自然繁殖状况趋于稳定。结合生态调度期、非生态调度期鱼类日均产卵规模的比值得出,除了2016、2020年生态调度期间没有出现大规模繁殖以外,其它年份生态调度的实施对促进产漂流性卵鱼类繁殖起到了积极的作用。建议今后继续加大三峡水库生态调度力度,针对不同鱼类物种的需求设计更精细的生态调度方案,进一步提升生态调度对长江中游鱼类自然繁殖的贡献。;From 2011 to 2020, Three Gorges Reservoir has conducted a total of 14 ecological operation experiments to promote the natural reproduction of the four major species of Chinese carp in the lower reaches of the reservoir. In order to capture the changes in the response to the natural reproduction of pelagic egg-producing fish since the implementation of ecological operation, and to evaluate the contribution of ecological operation to fish reproduction in the middle reaches of Yangtze River, a survey and study of early fish resources was conducted at a fixed collection point in the Shashi section of the middle reaches of Yangtze River from May to July each year. The results were as follows: In the past ten years, 35 species of drifting fish eggs had been collected, among which 25 species were typical drifting egg producing fishes, mainly including Hemiculter bleekeri, Parabramis pekinensis, Squalidus argentatus, Ctenopharyngodon idella, Hypophthalmichthys molitrix, Culter alburnus and Parabotia fasciata. The diversity index H, evenness index E and stability index ICV of the fish egg community showed the same trend of first decreasing and then increasing, but the dominance index D was the opposite. The inflection point appeared in 2017,indicating that community diversity tended to increase and community structure tended to stabilize since 2017. In general, the breeding size of fishes producing drift eggs first decreased and then increased, with a significant increase in eight fish groups since 2017. The peak frequency of fish breeding gradually increased, and the period of large-scale breeding gradually extended, indicating that the natural breeding situation of fish tended to be stable. Combined with the ratio of the average daily breeding size of fish in the ecological regulation period and the non-ecological regulation period, it was concluded that the implementation of ecological regulation in other years had played a positive role in promoting the reproduction of drifting egg-producing fish, except that there was no large-scale breeding in the ecological regulation period in 2016 and 2020. It is suggested to strengthen the ecological operation of Three Gorges Reservoir in the future, to design more detailed ecological operation plans that meet the needs of different fish, and to further enhance the contribution of ecological operation to the natural reproduction of fish in the middle reaches of Yangtze River.