Agreed that humans killing salmon is the lion's share of the problems facing salmon. I personally don't buy into any notion that sport fishing has led fish to evolve to bite less (though there may be some truth there). My experience has consistently shown that, all other things being equal, quality of fishing is directly proportional to the number of fish subject to the fishery.
In 2014, when we had lots of coho around, I got lots of bites. For crying out loud, I had Chinook taking trolled spinners about 4 inches under the surface that year, and that hasn't been the case in any other year I've fished. Past two years, few coho, and very few bites. Of course, after I realized the numbers were crappy, I didn't put in as much effort....