Fly choice in stained water depends on the color shift. In brown, muddy water or tannin-stained water with a yellow-brown color shift, I like a light tan-colored fl y contrasted with a bright secondary color, or hot spot. In the driftless rivers I call home, my favorite fly for the spring runoff period is a tan-colored scud with a bright pink hot spot. For the green-stained water common when algae concentrations rise in the summer, fish see a dark-bodied fly with green highlights well. Because light is attenuated in heavily stained water, I lean toward a dark primary-colored fly contrasted by fluorescent accents. Fluorescent colors are the least affected by color shifts.
Contrast is critical, and anglers should emphasize those characteristics in flies the more deeply stained the water. Most insects, smaller prey fish, and other prey species trout feed on have two-toned bodies—dark on top with a lighter underside—and contrast in flies is often a trigger for trout, much like a hot spot.
Central Processing: The Trout Brain
Anglers probably ascribe way too much intelligence to trout, but when we’ve been outwitted by them, most of us automatically want to attribute a much higher intellect to fish than is probably justified. There’s no conscious effort on the part of the trout to thwart our desires; more often than not, we’re just not offering a fish what it wants.
Like all predators, a trout forms its own mental “search image,” if you will (an archived image of food it’s eaten in the past), to help it decide what to eat in the future. It compares any new potential food items, including a fly, to a pre-established standard. If a fly matches something in the search image, you’re in business.
HOOK: Tiemco 3769, sizes 12 and 14.
THREAD: Tan 6/0.
BEAD: Fluorescent Pink Hareline Plummeting Tungsten Bead.
TAIL: Natural mallard flank.
RIB: Small black UTC Ultra Wire.
BODY: Hareline Ice Dub, UV Tan.
SHELL: Clear 1/8-inch Hareline Scud Back.
LEGS: Teased-out dubbing.
The search image is firmly entrenched with repeated exposure to the same prey species, which leads to food exclusivity, an activity sometimes called “selective feeding” when trout will accept a fly only if it closely matches the natural food item. When prey is less frequent, the search image is weak and fish will show more latitude in food acceptance. Doug Swisher and Carl Richards originally called this nonexclusive feeding pattern “opportunistic” in their classic book, Selective Trout. Opportunistically feeding trout will accept a wide range of different foods items and flies, provided they’re well presented.
The search image consists of four criteria: size, profile, color, and animation. Think of it as a checklist or set of criteria a fly must pass for a trout to accept it. If it passes all four tests, the fish will eat it, providing it imitates a food they’re currently eating. But remember, the search image is an inclusive list. Those items must be present for a food item to be accepted. It’s not an exclusive list, meaning that the presence of something that’s not on the list is not necessarily a negative. In other words, when fish examine food, they are looking for a reason to eat it, not for a reason to refuse it. After all, they’ve got to eat to stay alive, and if they were looking for reasons to reject a fly, the hook would be the most obvious deterrent.
Size is usually the first criterion a fly must match, since size can be judged at a distance. If our fly is larger or smaller than the naturals, it will stand out as phony at a glance. As the fly approaches a trout, shape is also obvious early on. Just as you can tell a minivan from a sports car a long ways off, if our fly is the wrong size or profile, it usually won’t stand a chance. If trout are completely ignoring your fly and you’re pretty sure it’s the right profile, try the same fly in a different size.
The color of a fly is most accurately judged at close ranges to avoid the effect of color shifts in water. If a fly’s color isn’t close to that of the natural, that difference may account for close-range refusals. If you’re seeing fish inspect a fly closely but ultimately refuse it, try the same fly in a slightly different color.
Animation, the fourth item on the search-image checklist trout use, is just as important as appearance. If a fly doesn’t act like it’s supposed to, fish won’t accept it. All food trout eat is alive and moves. For fly tiers, the small-scale movements of insect legs and gills are well imitated with natural and supple fur and feathers. The materials interact with the current to add a touch of realism. I also like rubber legs on flies that imitate legged insects; after all, it’s often the little things that matter. Think of a mountain lion seeking a deer—sometimes all it takes for the lion to attack is the flick of the deer’s ear or tail. Movement attracts attention.
The search image is not like a photograph trout use to compare food items. It’s more like a template. Therefore, our flies don’t need to be exact duplicates of the naturals; we can instead aim for impressionistic renderings of them.
The Pineal Gland
Sometimes called the trout’s “third eye,” the pineal gland lies at the top of the brain just beneath a section of skull that allows the partial transmission of light. It helps synchronize the trout’s rhythm to daily and seasonal cycles, but also serves as a “shadow detector” to warn of overhead threats. In fact, even fish that have lost vision in both eyes still respond to overhead shadows.
Understanding what trout see and how fish process visual information is vital to anglers because we seek to fool a predator that has discriminating eyesight with which to inspect our flies, backed up by a visual early warning system to alert it of danger from larger predators—including us! Although we’ll probably never know exactly what fish see, since we can’t look at their underwater world through their eyes, we have a pretty good idea of what they should see.
Jason Randall is the author of Trout Sense: A Fly Fisher’s Guide to What Trout See, Hear, & Smell and a frequent contributor to American Angler. Visit his website at www.jrflyfishing.com.