A synthesis of US Atlantic salmon habitat requirements and implications for future suitability under a changing climate

The Gulf of Maine hosts the southernmost remaining population of North American Atlantic salmon. Despite extensive hatchery supplementation since the late 1800s, and more recent riverine habitat restoration efforts and fishing restrictions, US-origin Atlantic salmon populations continue to decline and have remained at low abundance over recent decades. Climate change has been identified as a critical threat to the future of US Atlantic salmon. In this study, we synthesized available information on how habitats used by Atlantic salmon across all their life stages will be affected by climate change as well as the suitability of future conditions for salmon's persistence in the region. Maintaining sufficient cool water refugia during increasing summer temperatures in riverine habitats is required for sustaining salmon in the future. Changes in groundwater quantity and temperature, which will depend on future precipitation and temperature, will be critical factors for river temperatures, as will land use and land cover. While Atlantic salmon's freshwater life stages are heavily documented, the marine phase is relatively less studied. Climate models predict basin-scale changes over the next century, but impacts to salmon are difficult to predict. Furthermore, disparate drivers and differential rates of change between freshwater and marine habitats could present an obstacle to the transition between phases in the future. We have a general understanding of migration patterns and prey preferences but lack a clear picture of how salmon respond to habitat and ecosystem-level changes associated with climate change progression. More research to understand freshwater habitat changes and salmon's marine spatiotemporal distribution responses will enhance capacities to evaluate future risks and predict impacts of climate change to US-origin Atlantic salmon.

Automated summary

The Gulf of Maine is home to the southernmost population of North American Atlantic salmon. Despite conservation efforts, including hatchery supplementation, habitat restoration, and fishing restrictions, the population of US-origin Atlantic salmon continues to decline. Climate change is recognized as a significant threat to the survival of US Atlantic salmon, and understanding how their habitats across different life stages will be affected is crucial for conservation. While the impacts on freshwater habitats are well-documented, the marine phase of Atlantic salmon's life cycle is less studied, and predicting the effects of climate change on salmon remains challenging.