A study tracking salmon in the Fraser and Columbia rivers has determined that dams are not the main cause of Salmon collapse.
“dam modifications to assist migrating salmon have led to much-improved survival rates since the 1970s, the study team suggests.”
In other words, the core issue with Salmon survival is in the open ocean. This does not bode well for an easy fix.
“Possible negative factors include ocean warming and changes to salmon prey distribution, increased salmon predation by seals and sea lions, and lethal parasite infestations of wild smolts spread by coastal salmon farms.”