Reservoir impoundment affects fish habitat condition, in turn likely influencing the spatial and temporal distribution patterns of fish assemblage structure in the impounded area. Fishing activity and instream gravel and sand mining are important anthropogenic factors, and flow discharge, water temperature, and precipitation are important natural environmental variables; both anthropogenic and natural factors likely have impacted fish assemblage structure in impounded and unimpounded waterbodies. We used multivariate analysis to evaluate the combined effects of two adjacent reservoir impoundments in the main stem of a large river (Jinsha River; the upper segments of the Yangtze River), overfishing, instream gravel and sand mining, the natural flow regime, and other environmental variables (water temperature and precipitation) on fish assemblage structure in the Heishui River, a small, free-flowing tributary upstream of the mainstream reservoirs. Fish assemblage data and abiotic data collected over 10 years (2008, 2010, and 2011–2017) were analyzed. The results showed that fish assemblages of the Heishui River temporally clustered into two groups that were strongly associated with the two downstream cascade reservoirs (Xiangjiaba and Xiluodu reservoirs) in the main-stem Jinsha River. The relationships between fish assemblage structure and abiotic factors were tested using a distance-based linear model and were visualized using distance-based redundancy analysis, showing that the main factors explaining the interannual and seasonal variation in fish assemblage structure were instream gravel and sand mining, mainstream reservoir impoundment, and seasonal flow regime. Among these, instream gravel and sand mining in this tributary played the most significant role in affecting the temporal variation of fish assemblage structure and explained 34.12% of the total variability. Mainstream reservoir impoundment and seasonal flow regime exerted secondary effects on the temporal variation of fish assemblage structure and together explained 13.39% (7.00% and 6.39%, respectively) of the total variability. This study suggests that the relevant administrative agencies should focus more on free-flowing habitat maintenance in this tributary and the control of instream gravel and sand mining.

中文翻译：

---

西南金沙江支流鱼类群落对生境变化和捕捞活动的响应

水库蓄水影响鱼类栖息地条件，进而可能影响蓄水区鱼类群落结构的时空分布格局。捕鱼活动和河道采砂是重要的人为因素，流量、水温、降水是重要的自然环境变量；人为和自然因素都可能影响蓄水和未蓄水水体中的鱼类组合结构。我们使用多元分析来评估一条大河（金沙江；长江上游）的两个相邻水库蓄水库、过度捕捞、河内砾石和采砂、自然流态、以及其他环境变量（水温和降水）对黑水河鱼类群落结构的影响，黑水河是主流水库上游的一条小型、自由流动的支流。分析了 10 年（2008、2010 和 2011-2017）收集的鱼类组合数据和非生物数据。结果表明，黑水河鱼类群落在时间上聚集成两组，与主干金沙江下游的两个梯级水库（向家坝和溪洛渡水库）密切相关。鱼类组合结构与非生物因素之间的关系使用基于距离的线性模型进行测试，并使用基于距离的冗余分析进行可视化，表明解释鱼类组合结构年际和季节变化的主要因素是河道砾石和采砂、主流水库蓄水和季节性流态。其中，该支流的河道砾石和采砂对鱼类组合结构的时间变化影响最为显着，解释了总变异的34.12%。主流水库蓄水和季节性流态对鱼类组合结构的时间变化产生次要影响，共同解释了总变化的 13.39%（分别为 7.00% 和 6.39%）。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。干流水库蓄水和季节流态。其中，该支流的河道砾石和采砂对鱼类组合结构的时间变化影响最为显着，解释了总变异的34.12%。主流水库蓄水和季节性流态对鱼类组合结构的时间变化产生次要影响，共同解释了总变异的 13.39%（分别为 7.00% 和 6.39%）。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。干流水库蓄水和季节流态。其中，该支流的河道砾石和采砂对鱼类组合结构的时间变化影响最为显着，解释了总变异的34.12%。主流水库蓄水和季节性流态对鱼类组合结构的时间变化产生次要影响，共同解释了总变异的 13.39%（分别为 7.00% 和 6.39%）。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。该支流的河内砾石和采砂对鱼类组合结构的时间变化影响最为显着，解释了总变异的34.12%。主流水库蓄水和季节性流态对鱼类组合结构的时间变化产生次要影响，共同解释了总变异的 13.39%（分别为 7.00% 和 6.39%）。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。该支流的河内砾石和采砂对鱼类组合结构的时间变化影响最为显着，解释了总变异的34.12%。主流水库蓄水和季节性流态对鱼类组合结构的时间变化产生次要影响，共同解释了总变异的 13.39%（分别为 7.00% 和 6.39%）。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。分别）的总变异性。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。分别）的总变异性。本研究建议相关行政部门应更多地关注该支流自由流动的栖息地维护和河道砾石和采砂的控制。