三峡水库蓄水后长江中游宜昌江段鱼类早期资源群聚动态

基于2007～2018年葛洲坝下宜昌江段鱼类早期资源调查资料的整理分析,采用群落生态学方法对12年来长江中游鱼类早期资源群聚特性和年际变化趋势进行了研究,探讨了三峡水库蓄水后鱼类早期资源的优势种更替过程和群落结构变异.结果显示:12年间共采集到鱼卵5目9科49种,其中产漂流性卵鱼类28种.鱼卵物种数的年际变化趋势不显著,但年间变幅较大(18～30种/a).鱼卵丰度的年际变化表现出明显的趋势性上升,其中"四大家鱼"采集数量和密度呈先下降后上升的"U"型变化趋势.群落结构分析显示,12年间宜昌江段鱼卵物种多样性指数均呈缓慢下降趋势,并在2007～2008、2009～2013和2014～2018年形成三组不同的时间聚类,组间差异显著.SIMPER分析表明,各时期鱼卵群落差异主要受优势种和重要种所决定.2013年前,贝氏(鳖)(Hemiculter.bleekeri)、银鮑(Squalidus argentatus)、银鲴(Xerocypris macrolepis)、草鱼(Ctenopha-ryngodonidellus)等交替出现成为主要优势物种;2013年后,贝氏(鳖)成为主要优势物种,优势种和重要种的鱼卵数量占比进一步上升(大于90％).研究结果指出,2003年三峡水库蓄水后,葛洲坝下宜昌江段鱼类早期资源优势种更替现象逐渐消失,群落结构趋于稳定,繁殖鱼类群落结构正向"单一化"发展.

Dynamic of Fish Eggs Assemblage in the Middle Yangtze River After the Impoundment of the Three Gorges Reservoir

Based on the annual ichthyoplankton surveys under the Gezhouba Dam (GD) in the middle Yangtze River from 2007 to 2018, the assemblage of fish eggs and its temporal variation were studied using multivariate statistical analysis. This research aimed to investigate the change between the dominant species and the succession process in the species abundance and richness after the impoundment of the Three Gorges Reservoir (TGR). Over the past 12 years, 49 species belonging to 5 orders and 9 families were collected, and of which 28 species were drifting fish eggs. The species abundance varied from 18 to 30 between years and the egg richness increased significantly year by year. For the four major Chinese craps, the number and density of their eggs increased after an initial decrease. The diversity index of the fish egg community exhibit a slow downtrend, and three groups were identified using CLUSTER and nMDS. They were group A (2007-2008), group B (2009-2013) and group C (2014-2018). The SIMPER showed that the difference between groups was significantly and was mainly attributed to the turnover of the dominant species. Before 2013, The dominant species of fish eggs varied among Hemiculter Bleekeri, Squalidus argentatus, Xenocypris macrolepis and Ctenopharyngodon idellus. Since then, the eggs of Hemiculter. Bleekeri became the only dominant species. The results in our study showed that the species turnover became weak after the impoundment of the TGR, which indicated a structural decline in the fishery resources.