The dams will stay until an alternate way of generating power is found, be it fusion or whatever. Take CM's magic wand and all cars & trucks are electric, then ask where does the power come from? Wind, solar, geothermal could put a small dent in it but not much. Coal, nuclear, more hydro are out so where does the power come from? Until that question is answered with a cost effective alternative nothing changes. In fish terms our only approach can be to reduce harvest to match the productivity of individual watersheds which will mean you have to address mixed stock fisheries over harvest. Harvest will still happen but it will be terminal based or where stock overlap is minimal.