We need too keep remembering that what spawns is what survives to spawn. They are not caught in nets or by hooks, they are missed by the pinnipeds. I remember reading somewhere that the European Brown Bears are way smaller and much more secretive that Americans Browns. Maybe all those years of avoiding humans made then so. Same with the salmon. For a salmon, lockjaw is a survival advantage. Not riolling and jumping and calling attention to ones self works too. Sneak upstream.