Assessing climate change impacts on North American freshwater habitat of wild Atlantic salmon-urgent needs for collaborative research

Climate change and human activities have dramatically affected all ecosystems inhabited by Atlantic salmon, causing drastic population declines. Change in river temperature dynamics (e.g. daily variability, frequency, and duration of summer maximum, warmer thermal regimes) is of special concern as it impacts growth rates, reproductive success, prey abundance and phenology, timing of migration, and ultimately survival. The Atlantic Salmon Research Joint Venture held a workshop to address the effects of climate change on freshwater habitats of Atlantic salmon and identify research gaps and priorities. Here we summarize the state of the science for three key themes identified by workshop participants: (1) Effects of climate change on in-river habitat conditions, (2) Physiological and behavioral responses of salmon to temperature, and (3) Population-level responses of salmon to climate change. The group highlighted the crucial importance of understanding and monitoring the links between river temperature dynamics and physiological requirements of Atlantic salmon across different life stages and habitat conditions, with a focus on freshwater life stages. Climate change will undoubtedly continue to affect instream habitats across all seasons and render challenging conditions for all freshwater Atlantic salmon life stages. Hence, we call for urgent interdisciplinary collaborations and partnerships among scientists and managers to address the pressing research gaps that require large-scale data integration across life cycle stages and ecosystems. More collaboration between scientists, managers, and interest groups is needed to ensure that fundamental science directly addresses the knowledge-action gap to enhance evidence-based decision-making and conservation. Climate change and anthropogenic activities are affecting Atlantic salmon habitat characteristics, leading to physiological and behavioral changes that determine both the individual and population level potential for adaptability. Although climate change affects all aspects of the Atlantic salmon life cycle and habitats across the watersheds-ocean continuum, this workshop focused on changes in thermal and hydrological river regimes.