I think one of the major factors influencing smaller salmon is plainly selectivity. Years ago when I was getting my basic salmon understanding when volunteering at the hatcheries on my days off, I found out that the largest of the returning adults were used for hatchery stock. This made sense to me, because in the various fisheries, especially the gillnet fisheries, selected larger fish with appropriate mesh size. Over the years, the largest of salmon are taken by various fisheries. I'm now unaware of hatchery practices - if they select for large size or not. Years ago I learned that hatchery selectivity was across the board for size. What's the practice now? I don't know.

It seems to me that we're breeding, both naturally and artificially, a bunch of jockeys instead of defensive lineman. The smaller fish also diminish in fecundity, but good 'ol WDFW doesn't adjust the numbers to relate to that diminishment in viable eggs.