No question on the trend and I think you know what you are talking about. It is what is causing the trend that I question. Is it mainly pressure or are other things involved? I think legal sportie pressure as the answer is not complete.
What are the other things involved that also contribute? Has there been increased tribal harvest? Illegal harvest? Changed ocean conditions? (everybody blames this when they are clueless, a nice scapegoat,). Changes in logging/habitat? Weather? Hatchery release numbers?
Prolly not dams.