Fish no matter how large they become, they still refer to a predator prey relationship. All fish start off as small insignificant creatures, with many other larger fish willing to write their obituary with one fell swooping bite. So hence, the Salmon are a prey specie for things like seals, killer whales and numerous other beings of the deep. Also, a Salmon's mouth is not designed for slash and tear tactics like a Great White, They don't even have noticeable teeth until the last few weeks of life. I seen this personally every time I unhook a fish for a charter guest.
Fish hold their distance then turn on the prey with a slight turn of their head.
I seen this in the river when fishing for Steelhead in either clear water or shallow water while nesting on the redds many times. Also, let me add, we as humans have 3 color receptors, being red, blue and green. Fish can have up to 9 color receptors, depending on the specie. I know because I've missed fish with the net and brushed them, only to see a spent 30 pounder to get a new lease on life and peel 20 yards off the reel in a rapid fashion with me apologizing to the rod person. Fish feel movement and that's why the Dodgers and Bechold Rotating Flasher was so effective the last Salmon Season.