One day several years ago, when the afternoon light was exactly right, I saw a trout rise and then swim swiftly 20 feet away. Boy, was I surprised! Granted, it was in a flat, low gradient pool, so its behavior made sense. The point here is that trout have a tendency to move when feeding on floating flies. Risers may move an inch, a few inches, several feet, or swim in erratic patterns looking for flies, depending on the number of flies available and the type of habitat they are feeding in. 

Anglers that don’t make the connection with this type of feeding behavior will spend a lot of time changing flies and casting at ghosts.

And if I hadn’t observed that trout’s behavior, I probably would have cast toward the last rise, while the fish was long gone! These are things to look for:

Flat water feeders tend to be on the move, more so than trout that feed in rifles or runs. Therefore, before casting, it is important to determine if a trout is holding a feeding location or is on the move. It is easy enough to do; just watch to see if rises occur in the same location or far apart. A fish that is on the move can be extremely hard to rise because it is impossible to know where it will feed next. Unless, you find trout that are staying up and taking flies steadily, allowing you to determine a feeding pattern and direction, then lead the fish and just keep putting your fly out there with the hope that it will eventually take. If flies are not numerous and fish are moving about erratically, that’s a bigger problem. It’s like shooting skeet, except that a gunner knows where each clay pigeon is going.

Trout that feed in rifles and runs have a tendency to hold their feeding stations and don’t move as much as trout that feed in slower pools. They still move to take flies, just not as much. If your patience allows and you have a good hatch of flies with several risers, watch for a bit, just to observe movement of the fish. Then pick a trout and see how much it moves while feeding. Soon you will see that the flies do not drift in exactly the same place as they float along. As a result, your trout will move to intercept individual insects as they enter the fish’s cone of vision.

A trout’s cone of vision is a physiological feature that fly fishers must be aware of and understand, as it can impact whether a fly is taken or not. Unlike humans, trout have a very narrow binocular window of vision, so they can only see in front of them to a limited degree, because their eyes are on the sides of the head. A trout’s monocular vision provides a wide cone of vision, from which it can examine large areas of river depending upon the depth. For example, a trout that’s six-feet deep has a cone of vision of about five feet; at three feet, the cone is reduced to about two-and-a-half feet, and within six inches of the surface, the cone is about five inches. See the problem here? The closer a trout is to the surface, the less likely it will see flies outside of this small cone, so keep this in mind the next time you have a steady riser that is not taking your fly. It may because the trout has not seen it.