As an eastside steelheader, and one who discusses a lot of topics with our local fish biologists, a lot of our fish over here don't leave salt water untill Aug. and Sept. Some they have tagged aren't getting to Bonneville untill mid Oct. Not sure where your 8 month data comes from. Also, while you may not feel it ethical, we sure do have some good fishing over here, with multiple fish days being the norm for those with a little knowledge.
Incidentally, the Grande Rhonde has been very good this year, and should stay that way. Watch flows, best under 4500 cfs.