Atlantic Salmon Fish Passage and Dams

Atlantic salmon split their life cycle between freshwater and saltwater. When in freshwater, salmon have relatively safe conditions in a resource-limited environment. While in saltwater, they endure a risky existence in a resource-rich environment. This provides unique benefits, but also creates vulnerabilities since Atlantic salmon rely on both environments for their survival. 

Scientists and managers are gaining greater appreciation for this dynamic. They are focusing research and conservation efforts on both freshwater and saltwater environments to help ensure the longevity of the species.

Atlantic salmon have evolved to migrate in and out of rivers. We investigate how barriers in those rivers affect the productivity of Atlantic salmon.

Barriers to fish migration are a common threat to salmon. Dams alter the natural flow and dynamics of a watershed and hinder migration to and from freshwater spawning and rearing areas and the ocean. Dams that span rivers where Atlantic salmon live are considered a primary threat to the recovery of the species because they:

• Impede movements of migrating salmon
• Contribute to the artificial alteration of the species’ age structure 
• Prevent salmon from easily moving upstream or downstream when temperatures get too hot and they need to find cool water 

Minimizing the negative impacts that dams have on Atlantic salmon and other anadromous fishes is an important first step to restoring the productive capacity of our rivers. Managing the existence of dams and diadromous fish within our rivers is complicated and challenging. 

We work to quantify the impacts that dams are having on Atlantic salmon populations. These impacts can be large with downstream losses of Atlantic salmon smolts often exceeding 50 percent. We also work with partners to monitor the ecological impacts of dam removal. All of these efforts inform better management of the species and water resources.