AS SEEN IN THE NOV/DEC 2007 ISSUE

Every wonder how or exactly what fish see? Do subtle changes in shades of color really make a difference? Does depth play a role? Read on for a journey unlike no other and determine for yourself if consistent success on the water is really as easy as it appears.

Sport fishing could be considered a black art of sorts with each angling adventure being an experiment of trial and error for the novice and expert alike, acquiring incremental bits of improvement from each blue water campaign or backcountry flats session.

As a fulltime Gulf Coast guide, I, like many other rabid anglers obsessed with our great sport, need to possess an intimate discernment of our piscatorial quarry as a requisite to keep us at the top of our game. Throughout the seasons, absorption of vital strategizing information has generally been limited to migration patterns, lure and bait choices and optimum tidal phases, all of which are important factors to successful angling.

Learning more, requires we dive deeper to sub-surface depths, into a fascinating world, one in which few anglers conceptualize while strapped into a fighting chair battling a billfish or while perched on the foredeck casting the shallows for inshore game fish. This often overlooked world in which ‘what and how’ fish see is chock full of lore and miss-conception and as I found out, brims with eye-popping facts of discovery!

To appreciate and understand the unique eyesight adaptations as well as species-specific attributes of game fish, an abbreviated refresher course in basic fish eye anatomy is necessary. In general, fish eyes are not much different than human eyes, as fish possess an iris, lens, cornea along with a retina complete with rods and cones. Structurally there is an obvious absence of eyelids as the fish eye is constantly covered with seawater.

The outcome of amazing lens altering adaptations is superior underwater eyesight capabilities. In contrast to the flat, oblong human lens, a fish’s lens possesses spherical, dense properties allowing for greater focus upon refracted light on the retina. Remember, as humans, we can adjust the curvature shape of our lens to focus both long and short range. Fish, however, are unable to make that change but can position their lens back and forth from the retina much like the act of focusing a camera.

It could be argued that we benefit at times greatly from a fish’s wide 180-degree sub-surface field of view. Indeed, our catching success relies heavily upon pinpoint casting, savvy boatmanship and, of course, proper natural bait/lure presentation. Depending upon the angling situation, these are skills many might be lacking or in need of subtle refinement.

Patrolling the flats, positioning over the reefs or scouring the deep blue, game fish utilize overlapping vision from both eyes to virtually eliminate blind spots in their field of view. Coupling outstanding depth perception, sleek swimming motion and constant eye movement, makes up for that errant off the mark cast or trolling pass.

Furthermore, studies have shown that many species lacking stellar vision rely heavily on smell and taste for defense and feeding tactics. Nostrils located on their snouts for smell, taste organs on the tongue, distinct lateral lines and an inner ear linked directly to the air bladder, all assist with vibration detection.

Trolling or casting artificial lures molded to lifelike perfection, all attached to invisible lengths of fluorocarbon leader, have delivered the tools to make us better anglers. However, with a selection process often clouded with too many choices, possessing a greater interpretation of what happens to light and color after it enters the water will be paramount to staying on the bite, especially during periods of rapid climate or water quality changes.

Keeping it simple, what we see is the visible spectrum derived from the sun’s radiation, as wavelengths of light dictate the colors present in the visible spectrum. Short wavelengths encompass shades of green, blue and violet, while longer wavelengths include red, orange and yellows. While fish can see shades of color, they are also able to visualize shades of colors not present to us, ultraviolet included.

As light enters the water column, attenuation begins to take place as the light rapidly begins to loose its concentration. Scattering and absorption facilitate attenuation with the suspension of solids within the water column.

Coastal ecosystems such as the famed Everglades region or the dark inshore waters of Northeast Florida are excellent examples where the scattering of light is predominant. The higher the level of suspended solids, plankton and detritus, the less light penetrates the water column with the opposite effect of greater penetration in clear water conditions.

Fueling great debate among avid anglers worldwide is how absorption affects their angling practices and successes. Photosynthesis (chemical reaction) also plays a large role in light absorption as distinct wavelengths of color are absorbed at varying rates and depths. Quickly absorbed or diminished at shallow depths will always be longer wavelengths containing shades of red, yellow and orange moreover, penetrating to deeper levels in the water column are the shorter blues, greens and violets.

Applied to a horizontal direction in the water column, absorption or in laymen terms, filtering additionally determines to what depth light actually penetrates. Studies have concluded a general baseline of 60 percent of light consisting of all reds is absorbed within the first 10 feet. Depths of 30 feet absorbed approximately 80 percent of the total light including all yellows, oranges and reds. Working to depths beyond 30 feet, fading light takes on properties of blues and subsequently, black as all remaining color is completely filtered.

Available scientific data regarding color and light reaffirms that color choice is critical when selecting an artificial lure. However, the question still remains as to what exactly do our favorite species of game fish see?

While it is complicated to determine “exactly” what game fish see, at different scales, fish can distinguish shapes, estimate size and detect motion. Experiments have shown that movement may initiate stalking of prey from a distance as shape detection occurs at a closer range. Nevertheless, according to researchers, the visual capability of a specific species heavily depends upon the environmental conditions they habituate.

Here in Florida, our diverse saltwater fishery is uniquely inhabited by species possessing eyesight attributes of peculiarity and astonishment. Breaking the fishery down into three segments, redfish and bonefish prove popular in the shallows, grouper and snapper bring many to the rail on the reefs, and billfish match strength and wills in the deep blue.

So what eyesight adaptations do these popular Florida species possess?

Lucky for us inquisitive anglers, Dr. Greg Tolley, Professor of Marine Science and the Director of the Coastal Watershed Institute at Florida Gulf Coast University in Ft. Myers, (www.fgcu.edu) can enlighten us with a more focused understanding of these exciting piscatorial targets we passionately pursue through out the Sunshine State’s warm tropical waters.

Dr. Tolley is a past recipient of the Knight Fellowship in Marine Science from the University of South Florida where he earned his doctorate in 1994. Receiving millions of dollars in grants and contracts from NOAA, Nature Science Foundation and the South Florida Water Management District, Tolley’s research has been exciting and diverse.

He has authored many publications on estuarine ecology, deep-sea fishes, fish physiology as well as approaches in science education. An avid outdoor enthusiast, Dr. Tolley’s current research is focused upon the influence of freshwater inflow on estuarine ecosystems, the ecology of marine fishes, and the role of oysters in creating essential fish habitat.

Camouflage on the reefs

Probing the reefs first, popular snapper and grouper targets stage up and effortlessly zip in and out of a variety of natural and artificial structures. Distinguishing their next meal is nothing short of intriguing. 

“Living in these clear, well-lit shallow waters” says Dr. Tolley, “…allows reef fish the ability to see color, but not in the fashion that you and I can. Remember, very few vertebrates have fully trichromatic color (three types of cones, each sensitive to a different color light) as we do. Cones sensitive to red light have yet to be found in fishes.”

What reef fish do see is a wider range of color than coastal fish. The retinas of fish on the reefs are typically sensitive to blue-green to green light while their coastal neighbors are only sensitive to blue-green light. It is important to keep in mind that light attenuates with depth, as long wavelengths tend to diminish first. Even though snapper and grouper can detect certain colors, these colors may not be present at varying depths.

Additionally, Tolley says the bright color patterns of fish on the reef may appear bright and of high contrast up close, but at a distance, actually help these fish blend in with their surroundings. A vibrant fact to ponder while live baiting or deep jigging the edge.

Seeing in the deep blue

Beyond the reefs lies the abyss, a dark world of krill, currents and submerged canyons. Properties of light fade fast in the azure environment, a magical playground hosting many of the world’s greatest angling achievements and tales.

In this dark environment, does keen eyesight rule supreme or are other vital senses and biological adaptations assisting deep-water residents as they investigate our well-contrived baits and lures? The answer could be; our spreads are in the eye of the beholder!

“Billfish exhibit a number of adaptations for life in the pelagic fast lane, especially the ability to deep dive,” says Tolley. “These fish possess both rods (low-light vision) and cones (color vision) in their retinas. Swimming in an environment of low light, the large eyes of many pelagic fish allow for the retinas to have a larger surface area. Essentially, the more retinal tissue available, the greater the number of rods (low-light photoreceptors) and the higher probability of light (photons) hitting one of these rods and being detected.”

“Fascinating” best describes billfish’s ability to often spend 12 hours or more in succession diving into the deep for prey. At great depths, they run the risk of being less efficient hunters due to the lower water temperatures effect on metabolism. While most fishes cannot regulate their own body temperature at great depths, billfish can counteract the negative impacts of cold water.

Dr. Tolley explains, “To counteract the potential negative impact of cold temperatures on vision (and information processing in the brain), billfish, swordfish included, possess modified eye muscles that act as heat exchangers warming the retina and brain.”

“Depending on depth, these heat exchangers can maintain the temperature of the eyes and the brain 10-15 degrees Celsius warmer than the surrounding water. This heating improves the ability to detect rapid movement at such depths by a factor of 10 over fishes lacking such heat exchangers!”

In angling circles, billfish cannot be mentioned without discussing bioluminescence. When deep diving, billfish feed primarily on cephalopods (squid) as well as lantern fishes, both known to bioluminescent. “Curiously,” Tolley adds, “although some mid-water species living at 600-3000 feet in depth possess yellow eye lenses to help detect and distinguish bioluminescent light from light downwelling from the surface, little is known of any such adaptations in billfish.”

All of our big game targets do possess limited color vision, as cones are present in high density within their retinas but again, this does not mean they see color the way we do.

Incidentally, here in Florida, many offshore anglers witness the flashing colors that occur in lit-up sailfish feeding in the spread. Flashing colors are largely reflecting in the UV range. “This, too, is curious,” states Tolley “…because at least one study has shown that the lenses of billfish filter out UV light and they are therefore unable to detect it.”

Such mystery and allure is what continues to attract many of us to the deep blue.

Success in the skinny

It’s no secret that redfish and bonefish pose frustrating angling challenges. Bright tropical sunlight penetrates many of Florida’s famous flats refracting off the lightly colored substrate. Here, often a full spectrum of colors is present however; the act of a fish snatching up a well-presented offering in these glaring conditions might not be as easy as it appears.

While little information on the vision of redfish and bonefish is available, anglers might be surprised to learn how well these shallow-water game fish can see above the waters surface. According to Tolley, “Because light bends when it hits the water’s surface, moving from a medium of low density, air, to a medium of higher density, water, most fishes living in the clear shallows have a wide field of view above the water’s surface, essentially from horizon to horizon,” states Dr. Tolley.

Foraging primarily upon benthic organisms (shrimps, crabs, clams, worms), redfish and bonefish utilize smell as well as vision to capture prey that also includes baitfishes. Not finding any evidence of, but worth exploring, explains Dr. Tolley, “is the possibility that these prized shallow water species have the ability to detect polarized light.”

Detecting polarized light can be used to enhance the contrast of underwater targets. As studies have suggested with cuttlefish, on the flats, shallow water game fish could rely upon polarized light to facilitate the break down of natural counter shading (i.e., silver on bottom, green on top) camouflage employed by schooling silvery baitfishes. 

A conceivable theory to reflect upon in an arena glaring with shadows, shapes, tails and ghosts.

Today, the modern innovation we apply from available science has us dialing into the hot offshore bites and turning fish on in the shallows. “What and how” game fish see will remain a hot topic of debate and opinion. For now, we will have to wait for evolving science to further discern these piscatorial eyesight mysteries. While patiently waiting, we will surely remain focused, thrilled and hooked up!

1. GAG Grouper, 2. AFRICAN Pompano, 3. Dolphin, 4. GOLDEN Tilefish, 5. Bluefish, 6. Trout,
7. Bonita , 8. Snook, 9. MAKO SHARK, 10. Kingfish, 11. MANGROVE Snapper, 12. Bonefish

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