[Justin]

They have trapped the sea lions and returned to the other side of earth for many years. But the same sea lion just keeps coming back.

Due to human, the sea lions gained significant advantage and almost annihilated the salmons. In addition, majority of the damage is done by just a few individual sea lions, who are several times heavier than others thanks to the easy kills at the dams.

I see no alternatives other than destroying the dams, which seems to me, not so practical.