Climate change and its associated symptoms, such as warming air temperatures, glacier retreat, reduced snowpack, and increased variability in precipitation, are warming rivers and lakes. Such warming water temperatures threaten cold-water fishes in some regions. For instance, warm water temperatures can kill or harm anadromous Pacific salmon as they migrate upstream to spawning grounds. In this study, we assessed how tributaries, and their relative watershed properties, shape temporal and spatial dynamics of temperatures during the summer months in a salmon migratory river. We focused on the mainstem of the Babine River of British Columbia, an important migratory corridor for steelhead and the five eastern Pacific salmon species, but particularly for sockeye salmon that spawn in stream reaches above the Babine Lake, at the river’s headwaters. We discovered that large glacier- and snowpack-fed tributaries cooled the Babine River by approximately 2 °C over its 96 km length. Different tributaries played different temperature functions. Cooler and more glacierized rivers were associated with a bigger change in temperature between upstream and downstream sites. Understanding how water temperatures change during adult salmon migration, especially within riverscapes on the edge of potentially harmful temperatures, can help inform proactive management options in a warming world.

气候变化及其相关症状，例如气温升高、冰川退缩、积雪减少和降水变化增加，正在使河流和湖泊变暖。这种变暖的水温威胁着一些地区的冷水鱼类。例如，温水温度会杀死或伤害溯河太平洋鲑鱼，因为它们向上游迁移到产卵地。在这项研究中，我们评估了一条鲑鱼洄游河流的支流及其相关流域特性如何影响夏季月份温度的时空动态。我们专注于不列颠哥伦比亚省巴宾河的干流，这是硬头鲑和五种东太平洋鲑鱼的重要洄游走廊，尤其是在巴宾湖上方、河流源头处产卵的红鲑鱼。我们发现大型冰川和积雪供给的支流使巴宾河在其 96 公里长的范围内冷却了大约 2°C。不同的支流起到不同的温度作用。较冷和冰川化程度更高的河流与上游和下游站点之间的温度变化更大有关。了解在成年鲑鱼迁徙期间水温如何变化，尤其是在潜在有害温度边缘的河流景观中，可以帮助为变暖的世界提供积极的管理选择。