The construction and operation of dams represents one of the most significant anthropogenic impacts to the aquatic environment of freshwater ecosystems and includes changes in flow, temperature, water chemistry, sedimentation, and nutrient delivery. Despite the substantial changes caused by dams, we have a limited understanding of how dams influence important rate functions of fish, including growth rates. This study measured the growth rates of Rainbow Trout Oncorhynchus mykiss from successive captures of individually marked fish over seven annual increments within four river sections downstream of Libby Dam on the Kootenai River, Montana. We modeled the influence of hydropower‐related environmental variables on Rainbow Trout length and weight growth rates using linear mixed‐effects models. The top models predicting annual length and weight growth rates contained measures of water chemistry (ratio of total N to total P [N:P]) during the growing season, winter substrate coverage by the diatom Didymosphenia geminata, and an interactive term between winter D. geminata coverage and fish size at tagging. Winter D. geminata coverage and N:P were negatively correlated with annual growth rates, but the interactive term indicates that the influence of winter D. geminata coverage disproportionally affects smaller fish more than larger fish. We hypothesize that N:P and D. geminata are influencing Rainbow Trout growth rates through lower‐trophic‐level impacts. Top Rainbow Trout length and weight growth models explained 94.6% and 92.2%, respectively, of the annual variability in growth rates, of which 87.7% and 76.2%, respectively, were attributable to fixed effects. An experimental nutrient addition study and robust trophic monitoring efforts in the Kootenai River downstream of Libby Dam would be an effective means of independent corroboration of these study results. If successful, nutrient addition may be an effective management strategy to improve annual Rainbow Trout growth rates, mitigating for the nutrient retention occurring in the large reservoir upstream of Libby Dam.

中文翻译：

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一条受监管大河的虹鳟年生长的影响因素

大坝的建设和运营是对淡水生态系统水生环境的最重大的人为影响之一，其中包括流量，温度，水化学，沉积和养分输送的变化。尽管水坝造成了巨大的变化，但我们对水坝如何影响鱼类重要的速率函数（包括生长率）的了解有限。该研究测量了虹鳟Onkihynchus mykiss的生长速度从蒙大拿州库特纳伊河利比水坝下游四个河段中连续七个年度增减的单独标记鱼的捕获中获得。我们使用线性混合效应模型对水电相关环境变量对虹鳟鱼长度和体重增长率的影响进行了建模。预测年长和体重增长速度的顶级模型包含生长期内水化学的度量（总氮与总磷的比值[N：P]），硅藻Didymosphenia geminata覆盖的冬季底物以及冬季D之间的交互项标记时的双子叶覆盖率和鱼的大小。冬天D.geminata覆盖率和N：P与年增长率呈负相关，但交互项表明冬季双子叶蝉覆盖率对较大鱼的影响更大。我们假设N：P和D. geminata正在通过较低营养水平的影响来影响Rainbow Trout的增长率。顶级虹鳟的长度和体重增长模型分别解释了年增长率的94.6％和92.2％，其中固定影响分别是87.7％和76.2％。在利比水坝下游的库特奈河中进行的一项试验性营养添加研究和有力的营养监测工作将是独立证实这些研究结果的有效手段。如果成功的话，添加养分可能是提高虹鳟鱼年增长率的有效管理策略，以减轻Libby大坝上游大型水库中养分的滞留。