Salma's spot on that the long-term t=future of mykiss will involve the resident and anadromous components as they are more or less the source of each. It is much more advanced perspective than I heard voiced in WDFW when lots of residents were found in the Cedar; the recommendation was made to fish out the residents to leave room for anadromous.

There are lots of reasons why the Chahalis system, for example, has more trouble with mykiss than some the coastal systems. The Chehalis has a lot more development, is a much lower elevation stream, and for much of the mainstem is better bass and sunfish habitat; all of which mitigate against salmonids.

As to why some areas (states/provinces) appear to do better or worse one need only look at a few variables as a starting point. Human development and access, hydrology, land cover as habitat, and so on. The biggest one, though, will be the management umbrella. What are the actual goals and objectives of the managers? As bad as many here think WA has done with mykiss, BC is on track to wipe out (see Thompson as the poster child with Skeena to follow) major watersheds' worth of mykiss. Oregon doesn't have a Washington-level of tribal input on the Coast and likely does not have a WA-sized population in those rivers. Probably, too, the river size and access may factor in.

It is a very complex problems we are all probably guilty of seeing the problems as centering on our personal favorite boogy-man whether it be the ocean, nutrients, gill nets, and so on. We are all correct in that they are problems, but solving only one won't bring the fish back.