Just because man has altered environments does not mean that we can't try to restore them. There is also a very big difference between you suggestion to "control Herschel at the locks" and simply kill pinnipeds. Surgical removal of problem animals should never be a problem, like stock-killing predators. But killing them all is not the answer.

Also, the predators we are trying to control don't have a choice. To exist, pinnipeds eat fish. They don't have a choice. Humans do.

I believe our efforts at salmon restoration, and likely many other species, will fail because society does not want to change/compromise/accomodate. It's my way or the highway.