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Human activities and climate change threaten coldwater organisms in freshwater ecosystems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold‐water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short‐term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold‐water refuges. We review current understanding of cold‐water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold‐water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold‐water refuges be managed as distinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the foundation for an integrated framework that links science and management by (1) mapping and characterizing cold‐water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework provides a path forward for managing and protecting cold‐water refuges using existing and new policies to protect coldwater organisms in the face of global change. [ABSTRACT FROM AUTHOR]

Fishways have traditionally been designed according to the capabilities of salmonids, but other species may be unable to navigate such structures. To improve passage for the entire local fish fauna in a cost‐effective manner, pool‐and‐weir fishways can be reconstructed to a hybrid vertical slot design. Here, we contrast a typical short‐term before‐after monitoring approach with a long term data series to assess whether we could document an effect of the reconstruction on the numbers and composition of species ascending the Høyegga fishway in the Glomma River, Norway. We found a significant difference in the species composition ascending the fishway before (2014–2015) and after (2016–2017) reconstruction. Species diversity increased and the combined number of fish ascending the fishway approximately doubled, largely driven by greater numbers of European grayling and European whitefish. However, the variance of the total number of fish and their relative composition found in the long‐term monitoring data (1985–2013) exceeded the range of values found in the apparent short‐term change. We could therefore not reliably attribute the changes to the reconstruction, as they could perceivably result from other, unexplained factors. Although diversity increased, we did find evidence that the fishway remained species‐selective after reconstruction. We conclude that although there have been improvements to passage in the fishway, the potential fish migration has not been restored. [ABSTRACT FROM AUTHOR]

Across taxa, it is generally accepted that there are fitness advantages to rapid growth early in life. For stream-dwelling salmonids, however, high temperatures and associated energetic costs during the summer growing season might offset or even prevent the competitive advantage of large body size. Our overall objective was to understand the relative importance of factors that can cause variation in growth rates in an age-0 cohort of wild steelhead ( Oncorhynchus mykiss) in Idaho, USA, where temperatures approach, and temporarily exceed, their tolerance level. For individually tagged fish inhabiting the same stream reach, we found that growth rates were negatively related to fish mass (slopes of the two best approximating models were both −0.024). Comparing growth rates from 16 different stream reaches throughout the watershed, we found that temperature-induced metabolic cost was the single best approximating model ( AIC w i = 1.0) of the variation in individual growth rates. The bioenergetic model showed that mass-specific metabolic costs decreased with mass, but the absolute energetic demands increased over the same size range. Because temperature had a multiplicative effect on metabolic cost, our results suggest that the effect of food limitation increased with fish size. We conclude that high water temperatures pose energetic bottlenecks and can be a potentially strong mechanism limiting growth in juvenile salmonids in summer, particularly as streams in the region experience warming trends. [ABSTRACT FROM AUTHOR]