The Stillwater Fly Fisher: UVor Not UV?

Fly-tying materials labeled “ultraviolet” started appearing a few years ago and are increasingly found in fly shops and fly-fishing catalogues. There is much confusion regarding what advantage, or lack thereof, these products impart to the fish-catching abilities of flies made with them. Some of the claims may well be factual and others nothing more than marketing hype. Let’s take a look at some empirical field observations and then try to lay a science-based foundation from which we can make educated guesses.

Yes and No

About five years ago, I was invited to fish with angling friend and master fly tyer Phil Fisher at Diamond Lake in Central Oregon. Phil had a hot tip on where to fish and the description for a new Callibaetis nymph pattern that was supposed to be just the ticket there. I was traveling with another master tyer and angler, the late Jim Cramer. The night before, after a fabulous dinner and fine wine at Phil’s home in Sun River, we used Hareline UV Ice Dub Callibaetis (UV Grey works, as well) to fabricate a dozen size 14 Callibaetis nymphs tied in the AP style of Phil’s and my mentor, the late André Puyans. The dubbing product was interesting in that in natural light, it had a slightly iridescent, subtly flashy, gray/ purple sheen. Our flies had excellent proportions, as preached by Andy, but the abdomen and thorax colors were different from any of the many Callibaetis nymph patterns that we had seen and fished, including Mike Mercer’s Poxyback Callibaetis, Rene Harrop’s similar and effective creation, and Denny Rickard’s approach using his stillwater nymph style of tying.

We drove south to Diamond the next morning, arriving a bit late, but found our friends from the Davis Fly Fishers who had given the original tip. We proceeded to anchor on the west shore in 14 feet of water, and Phil showed us his two-fly rig, which consisted of the new UV Callibaetis nymph on the point and a Central Oregon standby, the red-and-white Snowcone, 14 inches up the rig, which used release indicators because of the depth. (See “Deep-Water Indicator Fishing in this column in the July/August 2015 issue of California Fly Fisher.) We set our deepest fly one foot above the sandy, weedy bottom and proceeded to catch an amazing number of fish from 12 to 21 inches long until the bite ended in midafternoon. In addition to preferring the nymph, the trout took our flies best when we cast our rigs out from the shadow of our boat and shortly after instituted intermittent six-inch pulls. We hooked five fish on the UV fly for everyone taken on the Snowcone.

Tired and enthralled by landing so many fish, I jotted down notes, trying to peg the reasons for our success. After securing our gear and the boat, I went for beer and nachos, while Jim and Phil set up their vises on a table outside our motel room at Diamond Lake Lodge and started tying more UV Callibaetis nymphs. We had lost many on 5X break-offs. We speculated on what might be the reason for our spectacular success, thinking that it could be the UV component in the flies. But the only two certainties that resulted from two days of wildly successful angling were that we were over large concentrations of fish and that we had a fabulous time.

As I write this, however, I just returned from three days of fishing and had success at Frenchman Lake with the UV Callibaetis pattern, casting to sighted fish in shallow water where colors are more distinct. That said, my partner did equally well with a classic AP soft-hackle emerger tied without UV materials. A day later, at Davis, the fishing was abysmal with any pattern. There simply aren’t many fish there this year. Two and three years ago, when water levels were lower and ample fish populations were more concentrated, the same UV fly worked, at times spectacularly. I always carry half a dozen.

Variables

To try to understand these equivocal results, I called an angling friend who had a distinguished career as a physicist at Bell Labs and later at Intel (he’s a Stanford and Princeton guy — one of his notable discoveries was in the laser optics field related to silicon chip etching) to ask about ultraviolet light and its relation to fish and fishing. He called me back after a thorough search. His only solid information was that UV light is invisible to humans, but not to trout, bass, and many other species of fish, that UV materials reflect light from that wavelength spectrum, and that the reflectance drops off rapidly as water depth and turbidity increases. The enticing purple iridescence in our f lies’ dubbing was not in the UV spectrum, and there might not have been much UV wavelength coming off the dubbed abdomen and thorax of those nymph imitations in 13 feet of water among weeds in a clear, but rich aquatic soup at Diamond Lake.

In other words, it turns out that there are lots of variables at work here. Let’s take a closer look at light, color, and aspects of human and fish vision.

Visible light is a portion of the electromagnetic radiation spectrum that radiates out from the sun. The full electromagnetic spectrum begins with long wavelengths known as radio waves, and wavelengths get progressively shorter across the spectrum, shrinking to microwaves, terahertz radiation, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. There is no precise boundary between the categories; the wavelengths fade into each other. Humans can’t see ultraviolet or infrared light, but we can feel the later as the warmth of the sun or the heat from a campfire. The UV band can cause skin cancer and eye problems and can exacerbate herpes simplex outbreaks on our lips if we forget UV protection.

Visible light of different wavelengths is seen as different colors. We use colors to help interpret the world, as do fish with color vision. There’s a tremendous evolutionary advantage given to a discriminating, more precise vision. Shorter wavelengths of visible light are seen as blues and longer ones as reds. Water absorbs the red end of the spectrum more easily than the blues. (You see light that’s reflected; you do not see light that’s absorbed.) At one yard down, 25 percent of the red light entering has been absorbed. The deeper you go, the less color can be seen. Depth reduces light penetration.

Fish and other vertebrates have eyes similar to ours. Rods in their retinas detect black, gray, and white, while cones, as in our eyes, detect color. Fish that live at depth have fewer color-perceiving cones. Yet trout, bass, and even goldfish are known to have keen color discrimination and preferences for particular colors in certain environmental settings. In a grade-school science project, I dyed fish food different colors and tested the preferences of several species of goldfish. They liked red flakes better, but their favorite food was my classmate’s guppies, which my science teacher absentmindedly put in my research subject’s aerated tank for a long weekend. It’s hard to beat live bait and scent. (See “Scents and Sensibility” in this column in the November/December 2016 issue of California Fly Fisher.)

Water quickly removes all wavelengths of visible light other than the blue end of the spectrum, and most fish have eyes adapted to see dim blue wavelengths, and some can perceive light on into the ultraviolet range. But very few bodies of water have the clarity of Lake Tahoe or the Bahamian flats on a clear day. Granitic watersheds, like we have in the Sierra, produce clearer runoff and contain less particulate matter. Fertile lakes such as Crowley, Davis, or Frenchman drain alkaline soils, which produces a rich biomass: plankton, algae, and organic particulate matter that further complicate visibility. Fish rarely see more than 50 yards under optimal visibility conditions. In algaefied, turbulent, or muddied waters, their vision may be measured in inches. Water vapor in the air filtering sunlight, a wind that ruffles the water’s surface, reflection, and refraction in the meniscus complicate matters further.

UV or Not UV?

So there are many components to the color and light equation, as well as many factors at work in the equation beyond one particular part of the sunlight spectrum. Because we can’t see UV light and fish can, we can be fooled by UV materials as much as the fish are. Spectrum Response Total UV doesn’t appear to be on the market anymore, but it was a spray product that was said to “create intense visual effects that trigger strikes by emitting UV light and visible light in lifelike colors that are proven to attract fresh and saltwater fish of every kind.” Lot’s of hype there! I’ve tried it a few times and have no opinion either way. It used acetone as a vehicle, and the residual odor may turn fish off.

On the other hand, hype for new materials aside, some natural materials reflect UV light. Birds see UV radiation, and some feathers, particularly white and bright colors such as orange reflect UV light. Perhaps the attraction of iridescence in peacock herl is because it is reflecting UV radiation. But even seen in marketing terms, the jury seems still to be out about UV products. I pulled out one of the big fly-fishing catalogues and found that there was lots of attention and hype given to UV materials. Another respected feather-and-fur merchant’s publication was devoid of the UV word, and a third took the middle ground.

There are very few axioms in fly selection. As one so-called expert said, “If bass have a favorite color, they are keeping it a secret.” Another expert commented, “Loud, smelly, vibration-ridden, red or bright-colored lures are the best place to start.” The most expensive swimbaits are big-buck trout imitations. They look so good that you could throw one in the frying pan, but to the best of my knowledge they don’t reflect ultraviolet light.

And when I went through my fly boxes I realized that many of my best flies are gray, brown, olive, black, or tan. I pulled out my crankbait boxes and found an abundance of Bomber Model A Fire Tiger baits. Their model with chartreuse and fiery orange coloration was my best plug in the Delta. Second place was taken by blues and blacks. Was it the visibility factor, or just that it is a good crawdad pattern? I had also bought and made lots of red-and-white creations, as this color combination at times seemed productive. So in the end, I’ve concluded that

UV products have their place and are worth trying, but you shouldn’t quit using the other materials you’ve collected over the years. Don’t forget that fly animation, proper proportions, and lifelike appearance are all important for drawing strikes. It’s often the buggy gray, brown, black, or olive imitations that seem to work best. And nothing works very well if you don’t put your fly in front of a fish.

Editor’s note: the debate as to “UV or not UV” has been occurring on the Internet for a number of years, so far with no firm conclusions. It has, however, generated tantalizing ideas, like UV perhaps being most important for trout at night. See, for example, discussions at ence/to-uv-or-not-to-uv/ and http://www.troutnut.com/topic/7879/ UV-spectrumand-trout. In 2009, a book was published on the subject, The New Scientific Angling: Trout and Ultraviolet, by Reed F. Curry. It is not without controversy.