The Smith River is a popular recreational sport fishery in western Montana, but salmonid abundances there are thought to be artificially limited by riparian land‐use alterations, irrigation water withdrawals, and high summer water temperatures. We used integrated networks of temperature loggers, PIT tag antenna stations, and in situ temperature mapping to investigate the thermal hydrodynamics and associated movements of PIT‐tagged salmonids at the confluence of Tenderfoot Creek, a major, unaltered coldwater tributary of the Smith River. Contrary to expectations, Tenderfoot Creek itself was not used as a thermal refuge by salmonids during periods of high water temperatures in Smith River; rather, its cool outflow plume into the main stem was used instead. Mean daily outflow water temperatures averaged 2.9°C lower than those of the Smith River during summer and ranged from 0.5°C to 6.1°C lower. Moreover, measured and estimated temperatures in the outflow were cooler (by up to 2.8°C) than in Tenderfoot Creek itself at times as a result of groundwater upwelling at the confluence. Detections of PIT‐tagged fish in the thermal plume increased, especially at night, when daily mean water temperatures exceeded 20°C in the main‐stem Smith River; more than four times as many PIT‐tagged fish were detected in the plume (N = 52) than along the opposite bank (N = 12), which ostensibly afforded better cover. Coldwater tributary confluences may provide superior thermal refuges for salmonids—cooler than the tributaries themselves—when water temperatures in river main stems are stressful.

中文翻译：

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在Montane支流汇合处的高温事件中，地下水上升调节热流体动力学和鲑鱼运动。

史密斯河是蒙大拿州西部最受欢迎的休闲运动渔业，但据认为，鲑鱼的丰富度人为地受到河岸土地用途变更，灌溉水抽取和夏季水温升高的限制。我们使用了温度记录仪，PIT标签天线站和原位温度测绘的集成网络，以研究Tenderfoot Creek（史密斯河的主要，不变的冷水支流）汇合处的PIT标签鲑鱼的热流体动力学和相关运动。与预期相反，在史密斯河水温高的时期，嫩足河本身并未被鲑鱼用作避难所。取而代之的是，它使用了进入主茎的冷流出羽流。平均每日流出水温平均为2。夏季比史密斯河低9°C，并且低0.5°C至6.1°C。此外，由于汇合处的地下水上升，有时测得的和估算的温度比嫩足溪本身要低（最高2.8°C）。在主羽史密斯河中，当日平均水温超过20°C时，在热羽中检出PIT标签的鱼的数量增加，尤其是在晚上。在烟羽中检测到带PIT标签的鱼的数量是其数量的四倍以上（主干史密斯河的日平均水温超过20°C时; 在烟羽中检出的带有PIT标签的鱼的数量是后者的四倍多（主干史密斯河的日平均水温超过20°C时; 在烟羽中检出的带有PIT标签的鱼的数量是后者的四倍多（N =  52），而不是沿对岸（N =  12），表面上提供了更好的覆盖率。当河流主干的水温充满压力时，冷水支流汇合处可能为鲑鱼提供更好的避难所，温度比支流本身凉爽。