It is simple cause and effect for any animal. How do you make a hatchery or wild run non biters? Use a hook & line that steadily removes the most aggressive and over time wella they don't bite well. How do you take a average 12 lb Coho to 6 to 8? Net them with a small mesh for several generations allowing a greater percentage in the pool of small fish and you will decrease size with time just as the marine fisheries are dictating the shrinking Chinook. This not new folks and was one of the first things I learned working with fish. The first thing Harry taught me was all things with salmon are proportional and when humans alter the gene flow things happen. This is not rocket science guys. Humans have been doing this to many creatures for a few thousand years. Seems somehow when it comes to fish we want to ignore fact and just plain basic common sense. Enviros blame habitat and many the hatcheries but the truth is WE are the problem because KILLING them for food and fun. Which I might add is compounded by a state government in denial and a governing agency that is lost in the wilderness.
I am a crazy environmentalist, but I agree both gill nets and sport fishing have had a impact.