salmon return to the river they were born in. Dams prevent their return. Barge transport does not work very well, hence fish ladders. No ladders, no fish. Then, going out to the ocean, the smolts must avoid being sucked into the turbines and killed, or eaten by birds. Then four years later when they return, they have to get by hordes of seals and sea lions.
So over the last hundred years how many salmon have been born in these rivers, if these rivers have been dammed up this whole time?
Never knew that fish were born. Interesting.