For number one, wolves may eat fish instead of larger animals because those larger animals may be going into hibernation and also the berries that a wolf may eat has also gone out of season, leaving the only choice really being fish.
For number two, over harvesting salmon is pretty bad when it comes to the environment. it takes away food from predators, like the wolves in number one, so they lose a source of food and it also takes away the salmons ability to eat the smaller organisms in the stream, so they're going to become overpopulated.