UV light: Why it Matters to Fishermen
November 16, 2017
Special coatings containing brighteners that give ice lures added visual appeal can in some situations help gamefish see and home in on our offerings from greater distances than untreated lures, thus boosting our catch rates.
A virtual explosion in the number and variety of optically brightened baits in recent years has sparked intense debate over what kind of treatments are most effective, as well as where, when, and how they aid our efforts to put fish on the ice.
With so much science and speculation surrounding the ever-intriguing topic of what fish see, we thought it was high time for a quick recap of the subject to help you factor UV, phosphorescence, and fluorescence into your hardwater presentations.
Let's start with phosphorescent, or glow, finishes. Many anglers have been using glow for decades. I personally recall zapping bluish-white, glow-in-the-dark teardrops with an old-school camera flash during nighttime crappie missions in the 1980s. Though decidedly unscientific, my experiences told me there was little doubt that as a jig's glow faded, my odds of catching a fish declined.
Glow finishes represent a form of luminescence — the process by which a material emits visible light when it is subjected to an energy source (such as a camera flash) or chemical reaction. In a nod to Thomas Edison, it's worth noting that luminescence is a type of cold light, whereby its atoms become excited and radiate light without being heated — compared to incandescence, which is light from heat energy.
As I learned from my nocturnal panfish experiments years ago, length and intensity of glow depend on the particular type of finish, as well as the light source. But the bottom line is glow, or phosphorescent, finishes continue to emit light after you remove them from the source of energy that coaxed their atoms into putting on a light show in the first place. This sets glow apart from fluorescent finishes, which require continual stoking from an external light source to work their magic. Also a form of luminescence, fluorescence is the process whereby a substance (like a lure finish) absorbs high-energy light of a shorter wavelength and emits lower-energy light of a longer wavelength.
This is pertinent to our presentations because the portion of the sun's solar radiation spectrum that is visible to humans and many species of gamefish ranges from violet (shorter wavelengths, higher energy photons) to red, which has longer wavelengths and lower energy photons. These longer wavelengths of light include high-vis shades of red, orange, and fluorescent green, depending on the fluorophore the manufacturer adds to the finish.
Fluorescent finishes can add to a lure's contrast and make it appear brighter. In human terms, think of the fluorescent vests worn by highway workers, emergency personnel, and other people whose safety depends on being seen. Although the clothing appears to glow, it's actually changing the sunlight it absorbs and emitting it in different wavelengths that are easier for us to see.
Ultraviolet (UV) light lies on the shallow end of the wavelength pool. Science tells us that short-wavelength UV rays fall outside that portion of the electromagnetic spectrum visible to humans and many of the fish we love to slide onto the ice, including walleyes, sauger, pike, and a variety of sunfish.
Collectively, these kinds of fish and their human adversaries lack a dedicated photoreceptor in the retina that is sensitive to UV light. However, many other members of creation, ranging from birds to butterflies — including trout, salmon, and other species — do have the receptors necessary to see UV.
Many species that can see UV light rely on it for a variety of purposes, from identifying a mate to finding food and avoiding predators. Only a few years ago, reindeer were thought to be the only mammals that could see UV. Scientists have since acknowledged that other mammals, including some mice, rates, moles, and bats, have UV powers. As research progresses, we'll no doubt learn more about what can see UV, to what extent, and how it affects behavior.
Regardless of the latest scientific line on the subject, UV jigs, jigging spoons, softbaits, and do-it-yourself coatings are all the rage on the ice-fishing and open-water scenes, and not just for salmonids. And many highly respected anglers have reported improved catch rates using UV-enhanced baits in a variety of settings.
Perhaps the truth about UV lies somewhere in the middle. When certain fluorophores are activated by "invisible" UV light, they re-emit it as longer-wavelength light within the visible spectrum. This phenomenon explains why a lure that looks pale in indoor lighting springs to life like a blacklight poster on a teenager's wall when hit with UV rays. Astute anglers like In-Fisherman's Dr. Rob Neumann, a student of the UV craze and fish vision in general, point out another caveat to the practical applications of lures coated with UV brighteners.
"If, and how much, a UV-enhanced lure fluoresces depends on how much UV light from solar radiation filters down to the depth at which you're fishing," he says. "Factors including chlorophyll content and dissolved organic matter have been proven to affect how much, and how deep, UV light penetrates the water column."
For example, in gin-clear lakes with very little to stop it, UV can radiate into depths of 100 feet or more. But in lakes with significant organic matter, it may penetrate less than a foot, Neumann says. "The scientific literature includes several studies where UV penetration was measured, and those depths can vary considerably depending on clarity and other properties of the water. In Crater Lake, Oregon, one of the clearest lakes known to exist, UV can penetrate over 300 feet. But most lakes we fish aren't that clear and contain more dissolved matter, which limits the depth UV can penetrate. Even within a geographic region, how deep UV penetrates in one lake can be quite different than in another."
Further complicating the conversation is that visible light can at times penetrate deeper than UV light — which runs counter to what many anglers believed at the outset of the UV revolution. "While UV does penetrate deeper in the most extreme water clarities, we now understand that UV penetration is affected by organic matter and other variables, and in most cases doesn't descend as deep as visible light in the waters anglers typically fish," Neumann explains.
By now you're probably wondering whether the ice also affects UV light penetration and the effectiveness of UV brighteners on our lures. Neumann's review of studies suggests that very clear lake and river ice is largely a non-factor in stopping such rays. "Organic matter responsible for preventing UV penetration is largely excluded during the freezing process," he says. "In fact, studies have shown UV light cut through clear Antarctic ice packs over 10 feet thick."
However, while clear ice is transparent, snow cover or cloudy ice is a buzz killer for solar radiation. "UV rays are highly reflected by white, fresh snow and white ice," Neumann says. "One experiment in Quebec showed 2 cm (less than an inch) of snow on top of three feet of ice reduced the under-ice exposure of UV light by a factor of three, compared to snow-free ice." Science may have a long way to go to fully explain the UV factor in ice fishing, but veteran anglers like Guide Brian "Bro" Brosdahl are convinced that optically brightened finishes help them catch fish — and not just in low light or low-vis conditions as originally thought.
"Anglers chasing trout, salmon, and walleyes were quick to embrace UV finishes, but such products have as many, if not more, applications on the sunfish front," he says.
Brosdahl, who spends much of his winters connecting clients with fish and working with companies to develop new products or tweak existing lineups, reports that optically brightened baits shine for sunfish under sunny skies in clear water. "Bluegills have amazing vision," he says. "They can see things we can't even imagine. So it's no wonder they're attracted to even subtle reflections from UV light during the day. I've found that switching from regular colors to UV finishes turns fish that were just sniffing my jigs into strikers, in gin-clear water in broad daylight."
Brosdahl adds that Northland Fishing Tackle's Mooska Tungsten Jig is one of his favorite UV bluegill baits, thanks to its sparkly and reflective UV GraniteGlitter coating. Available in panfish-friendly 1/57- to 1/16-ounce sizes, it also sports glow-in-the-dark eyes for extra attraction after dark.
Brosdahl's findings support scientific research stating UV penetration is greatest in clear water. The presence of glow on his pet UV jigs also brings us to a point brought up by Neumann. "Lures painted with a combination of phosphorescent and fluorescent finishes can complement each other, with one form of added attraction taking over as the visual trigger when conditions limit the other's performance," he says.
He also cautions not to put all your presentational eggs in the vision basket. "Also consider other aspects including working depth, sound, vibration, scent, and jigging patterns," he says. "At times any and all of these factors can be more important to a successful ice-fishing presentation."
*Dan Johnson of Isanti, Minnesota, is a frequent contributor to In-Fisherman publications and director of All Creation Outdoor Media.