Here's another thing to think about - fish eyes do not iris, and though they can see much better in the dark than we can, they can only adapt their eyes to changes in light by chemically activating or deactivating rods and cones in their eyes, and do so at about the speed that the sun rises and sets. Think of this as stepping into a darkened theater and taking an hour for your eyes to adjust enough to find a seat. This has implications for escape from predators in the unnatural situations we build for them - like continuous pier aprons in our industrial waterways. Why do those Green River fish runs seem to be failing? Well, picture this, downstream come the smolts and they run into a pier. They can't see under it so they go around it. They are then in deep water where diving ducks can attack them from all sides and push them against that black hole that is the unnatural shadow under the pier where they can't see and the diving ducks, who's eyes iris, can. Same for returning adults, this time it's the seals who bottle them up against vertical riprapped shorelines and pier aprons and feed away. The fish don't have anywhere to run or hide and they don't have a chance. All the harvest and hatchery impacts pale in comparison to the habitat impacts in this situation