三峡水库生态调度试验对四大家鱼产卵的影响分析

2011年以来，三峡水库持续开展了促进长江中游四大家鱼产卵的生态调度试验.采用鱼类早期资源调查方法研究了三峡水库生态调度实施以来四大家鱼自然繁殖、水文环境要素的年际变化特征，采用系统重构方法分析了四大家鱼自然繁殖的关键生态水文要素，提出了宜昌江段涨水过程的生态调度优化条件.结果表明:①2012—2018年三峡水库共开展了11次生态调度试验，生态调度使得宜昌江段持续涨水时间范围为2~9 d，水位日均涨幅范围为0.43~1.83 m，流量日均增幅范围为1 080~5 800 m3/s，起始水温范围为17.5~23.5℃.②沙市江段监测到四大家鱼鱼卵时的水温分布范围为19.2~25.5℃、平均值为22.5℃，流量分布范围为11 000~33 600 m3/s、平均值为16 890 m3/s；水温平均值在各年份间没有显著性差异，流量平均值在各年份间有显著性差异.③沙市江段四大家鱼鱼卵组成以草鱼和鲢为主，二者年均产卵量约占总产卵量的85%，青鱼和鳙年均产卵量约占总产卵量的15%.除2016年外，生态调度期间四大家鱼的产卵量占监测期间四大家鱼总产卵量的比例较大，变动范围为31.90%~66.58%.生态调度期间，四大家鱼自然繁殖性能普遍好于非生态调度时期，表现为产卵持续时间更长、产卵场范围更广、单次洪峰的产卵规模更大，证实了实施生态调度的有效性.④持续涨水天数、初始水位和产卵时序是影响2012—2018年宜昌至沙市江段四大家鱼产卵量的重要生态水文参数.⑤为增加宜昌至沙市江段四大家鱼产卵量，宜昌江段需满足的水文条件为断面初始流量达14 000 m3/s，持续涨水4 d以上，水位日涨幅平均大于0.5 m，流量日增幅平均大于2 000 m3/s，与前一次洪峰的间隔时间在5 d以上.研究显示，三峡水库连续实施生态调度对近年来长江中游四大家鱼的种群恢复起到了一定的作用，未来应将建模和监测手段整合到生态调度试验中以分析长期的生态响应，并建立一套科学的生态调度效果评价体系来评价流量调节对四大家鱼产卵活动的影响. 

Three Gorges Reservoir Ecological Operation Effect on the Spawning of the Four Major Chinese Carps

Since 2011, ecological operation tests of the Three Gorges Reservoir (TGR) have been continuously conducted to improve the spawning quantity of the four major Chinese carps (FMCC) below the Gezhouba Dam. This study evaluated the interannual variations of the spawning quantity of FMCC and the hydrological and environmental factors using an early fish resource investigation, and analyzed the key eco-hydrological factors affecting the spawning quantity of FMCC using a system reconstruction method. Based on the results of the system reconstruction, the flood process in the Yichang River Section was optimized for TGR ecological operation. The results show that: (1) A total of 11 ecological operation tests were carried out during the period of 2012-2018. As a result of ecological scheduling, the water level in the Yichang River Section continued to rise for 2 to 9 days. In these flood courses, the average daily rise of water level ranged from 0.43 m to 1.83 m, the average daily increase of flow ranged from 1, 080 m3/s to 5, 800 m3/s, and the initial water temperature ranged from 17.5 ℃ to 23.5 ℃. (2) When the FMCC eggs were collected, the water temperature ranged from 19.2 ℃ to 25.5 ℃, with an average value of 22.5 ℃, and the flow distribution range was 11, 000-33, 600 m3/s, with an average value of 16, 890 m3/s; There was no significant difference in the water temperature between years, whereas significant difference in river flow between years could be detected. (3) Grass carp and Silver carp were dominant species in egg composition of FMCC, accounting for about 85% of the annual average spawning quantity of four carps, and Black carp and Bighead carp accounted for about 15%. Except for 2016, the spawning quantity of FMCC during ecological scheduling period accounted for a large proportion of that during monitoring period, with a range from 31.90% to 66.58%. During the periods of the TGR ecological operation, the FMCC showed a longer spawning duration, a wider distribution of spawning grounds, and a larger spawning scale at a single flood course. (4) The number of days for continuous water rise, initial water level and spawning date batch were important eco-hydrological parameters affecting the spawning scale of FMCC in the Yichang-Shashi River Section from 2012 to 2018. (5) In order to improve the spawning quantity of FMCC in the section from Yichang to Shashi, the hydrological conditions of the Yichang River Section should meet following conditions: the initial flow of the section is above 14, 000 m3/s, the water level continues to rise for more than 4 days, the daily average water level rises more than 0.50 m, the daily average flow increases by more than 2, 000 m3/s, and the time interval from the last flood peak is more than 5 days. The research shows that the continuous implementation of the TGR ecological operation has played a certain role in the population restoration of the FMCC in the middle reaches of the Yangtze River in recent years. Future research should be focus on integrating modeling and monitoring methods into the flow regulation experiments to analyze the long-term ecological responses and establish a set of scientific evaluation system to estimate the effect of flow regulation on the FMCC spawning activities.