As to the peer-reviewed literature on overharvest take a look at Stockner's "Restoring Nutrients in Salmonmid Ecosystems". While the papers contained in it are not specific to steelhead or Puget Sound, they lay out a convincing case that the "cultural oligotrophication" (excessive fishing) of watersheds substantially reduces productivity which leads to smaller runsizes.

The literature is out there. It is just being ignored.