Rear Blind Spot
Extending the edges of the fish’s binocular zone rearward defines the limits of its field of vision, or so theory says. The theory, furthermore, promotes the idea that the limits of the fish’s peripheral vision clearly establishes a 30 degree blind spot to the fish’s rear. Therefore, the theory continues, one can sneak up on fish from the rear, and they’ll never see you. Only problem is, this is theory, not reality, and it doesn’t consider all the ramifications of the fish’s ability to see the angler.
First, the fish’s eyes bulge a bit, and they can actually see further to the rear than simple line drawings would indicate. Second, the fish can rotate its eyes rearward, enhancing its rearward view. Third, the fish’s swimming movements wiggle its head side to side slightly, constantly shifting whatever blind zone really exists. But far more important, the part of the angler that spooks the fish is the part above water, and the rearward blind zone doesn’t exist when the fish is looking up at its window.
The reason that anglers can “sneak up” on fish from the rear is because fish are normally looking upstream for food, and their attention is thus aimed upstream. It’s really not hard to “sneak down” on a fish, either, if one moves slowly, wears “environmentally friendly” clothes (read, colored like the stream side vegetation), and keeps the casting to a minimum. I’ve done it hundreds of times on smooth waters like Henry’s Fork, Silver Creek, the Test and Itchen, New Zealand’s crystalline waters, and many other similar waters.
The fish’s eyes are especially sensitive to contrast and motion, and doing anything that exposes you to that sensitivity is a sure-fire way to spook the trout. Be the predator that you have to be.
The rear blind spot is 30 degrees in theory, far less in actuality, and non-existent when the fish is looking at the surface.