There are many predators out there killingthe salmon and steelhead. Not the least of which are chemical pollution, poor logging practices, over grazing, pesticides, gill nets, dams, poachers, etc, etc.
I just learned of a study on the Columbia that found that mergansers are one of the very worst salmon and steelhead smolt killers.

Yeah, I would like to see some control on seals and sea lions. But I bet it would be much easier to do something about the mergansers, and it appears they are at least as big a problem. Sometimes that ugly thing we see, like a sea lion shredding a salmon have a huge impact when some of the things we don’t see are as bad or worse.