We tested for effects of two dams on fish assemblages in the St. Joseph River, Indiana. Fishes were collected by boat electrofisher twice annually, at 23 sites from 1998 to 2018. Fish collection data were aggregated into CPUE counts of species per 500 m, and CPUE were pooled across sites above and below the dams. We used multivariate analyses to test for spatial and temporal variation for assemblages above and below dams. Assemblages above and downstream of the dams differed significantly when examined by collection year. The effects (abundances of fish species) of the dams on fish assemblages were different at the South Bend dam from those at the Elkhart dam. Trajectories of temporal change in fish assemblages above and below dams were all gradual and directional. Temporal variation in fish abundance categorised into trophic traits (guilds) differed by location. We suggest that moderate to high stress from anthropogenic impacts on the St. Joseph River appears to result in high assemblage variation above and below dams. The St. Joseph River fish community appears to be unstable, likely from multiple anthropogenic impacts to water quality, habitat degradation and hydrologic alteration. We found that 25 of 33 hydrologic variables in four of five Indicators of Hydrological Alteration groups were significantly altered from 1931 to 2019. However, hydrology variation as potential disturbance events did not visually match observed temporal assemblage variation.

中文翻译：

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印第安纳州圣约瑟夫河流域的鱼群：主干水坝的影响

我们测试了两个水坝对印第安纳州圣约瑟夫河鱼群的影响。从1998年至2018年，每年通过船用电钓者在23个地点收集鱼类。鱼类收集数据汇总为每500 m的CPUE物种计数，CPUE汇集在大坝上方和下方的各个地点。我们使用多变量分析来测试大坝上方和下方的组件的时空变化。按收款年份检查时，大坝上方和下游的组件差异很大。南本德水坝的水坝对鱼类群落的影响（鱼类种类丰富）与埃尔克哈特水坝的影响不同。大坝上方和下方的鱼群的时间变化轨迹都是渐进的和定向的。鱼类丰度的时间变化归类为营养性状（行会），随位置而异。我们建议，人为地影响圣约瑟夫河的中度至高应力似乎会导致大坝上方和下方的高度组合变化。圣约瑟夫河的鱼类群落似乎不稳定，可能是由于多种人为因素对水质，栖息地退化和水文变化的影响。我们发现，五个水文变化指标组中的四个中的33个水文变量中的25个在1931年至2019年之间发生了显着变化。但是，由于潜在的扰动事件，水文变化与视觉上观察到的时间组合变化并不相符。约瑟夫河似乎导致大坝上方和下方的高度组合变化。圣约瑟夫河的鱼类群落似乎不稳定，可能是由于多种人为因素对水质，栖息地退化和水文变化的影响。我们发现，五个水文变化指标组中的四个中的33个水文变量中的25个在1931年至2019年之间发生了显着变化。但是，由于潜在的扰动事件，水文变化与视觉上观察到的时间组合变化并不相符。约瑟夫河似乎导致大坝上方和下方的高度组合变化。圣约瑟夫河的鱼类群落似乎不稳定，可能是由于多种人为因素对水质，栖息地退化和水文变化的影响。我们发现，五个水文变化指标组中的四个中的33个水文变量中的25个在1931年至2019年之间发生了显着变化。但是，由于潜在的扰动事件，水文变化与视觉上观察到的时间组合变化并不相符。