07/04/10
Insects and other foods the trout may be eating:
1.    Blue-winged Olives
2.    Cinnamon Sedges (Caddisflies) (Abrams Creek)
3.    Green Sedges (Caddisflies)
4.    Little Sister Caddisflies (Abrams Creek)
5.    Little Yellow Stoneflies -Yellow Sallies
6.    Slate Drakes
7.    Little Green Stoneflies
8.    Golden Stoneflies
9.    Ants
10.  Inchworms
11.  Beetles
12.  Grasshoppers
13.  Hellgrammite
14.  Cranefly
15.  Sculpin, baitfish and small crayfish (Imitate with streamers)


New Series on Fly Selection and Presentation - Part 6
Note: If you missed parts one through 5, please read them.

Trout cannot see nearly as well as us humans and you better be glad they can't. If
they could, none of your flies would fool the wild ones. In general, our human vision
is much better but as mentioned in the previous articles, the trout's vision is
perfectly suited to its needs. It is excellent for detecting predators coming from any
direction and it's perfect for the way trout feed. In essence, that is why they have a
vary wide peripheral vision and a very narrow binocular vision. Their vision leaves
only about a thirty degree blind spot behind them but even that is deceptive. We
approach trout from their rear thinking they can't see us but the slightest movement
of their heads, eliminates the blind spot. When a fish swims, it doesn't have a blind
spot at all. It isn't so much they can't see behind them as it is that when they are
feeding, they are focused on food drifting downstream.

Their eyes point slightly upwards. This means their cone of vision is slightly upward.
The fish can be in a horizontal position, which they almost always are, yet see
straight up over they head for food and prey. This fact makes it more difficult for the
trout to concentrate on the bottom. To do that using its binocular vision, the fish has
to raise its tail up and point down towards the bottom. That's why fish are seen
tailing when feeding. If they do this in very shallow water, you can see their tails.

When they are watching the surface for predators they can also spot drifting food
because of the movement of the food. They much turn their heads toward the food
in order to see it clearly. I mentioned that yesterday. If you cast a fly to their side,
they can detect the movement of the fly in their peripheral vision but they have to
turn their head to see it in any detail or for it to get in zone of binocular vision.

Here's another thing important to know about how a trout sees its food and
predators. If they are feeding in the surface film or feeding lane in fast water, they
have to get near the surface to have the time to catch the food when they see it. If
they are in moderately flowing water, they hold deeper because they have more
time to reach the surface. If they hold very deep and watch for food on the surface,
they have to swim through a lot of water to reach it. So what, you may think but
consider this. When the trout is only six inches deep, it can only see an object such
as food or a floating insect clearly that is within ten inches. This means if your fly
doesn't come into that small window of vision of ten inches in diameter, the trout
won't see it.  Everything else is out of focus. Remember the finger thing from
yesterday? If the fish is a foot deep is can only see something it is focused on
clearly that is within about two feet. Here is where it gets deceptive. If the fish is two
feet deep, it can see an object thirty feet from it. However, remember when fish see
through their window of vision, distant objects near the edge of the window appear
distorted.

What does this have to do with fishing? Well, for one thing it means if a fish is
holding two feet deep with the surface of the water fairly smooth, it can spot you
over twenty feet away. Technically, it can spot you thirty feet away. In either case,
you will be shorter than you are tall. The reason I say technically, is because if you
are under ten degrees of horizontal from the fish, you are in a very dim area due to
light refraction. You probably wouldn't be noticed at all. Remember too that is you
are motionless, or if you don't stand out in sharp contrast from everything else, you
won't frighten the fish. However it will be flee it the object or you move. If the trout is
holding in six inches of water, you can approach it much closer. There's something
else about this I must also point out. As many of you know, it isn't easy to judge the
depth of a fish.  

Without diagrams, which I haven't taken the time to do, it is difficult to explain the
windows affects on the trout's vision. But to put it simple, if you want to stay under
ten degrees of horizontal where you are in the dim or fringe area of the window, you
have to consider the depth of the trout. The shallower they are, the easier it is for
you to approach them without spooking them. The deeper they are, the lower you
have to be to remain unnoticed.