June 16, 2013
Understanding the physical capabilities of the fish we seek plays a role in making decisions about fish location and presentation. It's all part of the game.
Panfish, especially crappies and bluegills, tend to be sight feeders, which means they prefer to see it before they eat it. But what's to see under 3 feet of ice and 2 feet of snow?
Light is diffuse under hard water. Scattered by ice and snow cover, light penetrates but seems to come from all directions. It's a world without shadow, but hardly a world without light. During the day, it's not as dark down there as logic might suggest. In fact, it can be quite bright. Even at night, panfish can sight feed under the ice in slightly cloudy to clear water, but probably require a little more help from their lateral line (which picks up vibration) in the dark.
Many studies have been done on the visual acuity of panfish. The ability to see and feed on individual zooplankters has stimulated lots of scientific attention. The eyes of fish are similar to our eyes, with the same basic construction of cornea, iris, lens, and retina. Like us, panfish have multiple cones in the retina that allow for color differentiation. Laboratory tests with bluegills, sunfish, and the closely related black basses seem to indicate that these fish can distinguish one color from another.
So, panfish have the same eyes we do. But different. It's different underwater. Fish vision expert Dr. Don Quick has likened the optical landscape of fish to walking into a thick, midday fog, where even close objects are obscured by the light reflecting off millions of droplets of water in front of our eyes. The shape of the eye of any fish is specialized, to some degree. In the case of panfish, large, flat, bowl-shaped eyes allow more light in, and focus well on the tiny things panfish need to forage on to survive the first year. But no type of eye construction can see a long distance in fog.
The length of the visual field of panfish depends on water clarity. The maximum distance a fish can see underwater tends to test out about the same as a Secchi-disc reading, which is the distance at which a black-white Secchi disc disappears underwater under bright conditions. This is similar to the distance it takes for a big white jig to disappear under the hole. If your big, bright jig disappears about 10 feet down, it's safe to assume that the visual field of panfish is limited to slightly more than 10 feet.
BLUEGILLS AND SUNFISH
When bluegills see something that might be food, they reorient themselves and basically go on point, directing the long axis of their bodies in a line with the item that caught their attention. Fisheries biologists and researchers use this reorientation process to determine "reaction distance." Studies on reaction distance provide some idea about how close a jig has to be from a bluegill to elicit a strike.
A study carried out by William Walton (University of California), Jamie Emiley (Yale), and Nelson Hairston, Jr. (Cornell) focused on the effect of prey size in determining reaction distances in bluegills. They began by sorting daphnia, a species of zooplankton, into three size ranges, from .03 mm up to 2.3 mm in length. Each size group was stored in a separate tissue-culture well and introduced to a tank holding bluegills one at a time by a pipette placed at the opposite end of the tank from the fish. The tank was wrapped in white paper to reduce outside distractions.
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The term "maximum location distance" (MLD) was used to indicate the outer boundaries of reaction distance. Results included the affirmation that bluegills moved farthest for the biggest prey, again indicating the importance of vision in their foraging strategy. The farthest any bluegill reacted to the largest daphnia was about 46 cm (approximately 17 inches). Considering the size of the prey involved -- smaller than 1/32 of an inch -- that's a remarkable distance. (Extrapolating that to a 3/4-inch jig-maggot combo, reaction distance would be about 34 feet.)
Of course, the water was clear in the aquaria used in this study. The cloudier the water, the shorter a bluegill's range of reaction distance becomes, also indicating the importance of vision in their hunting strategy. In a study on turbidity and bluegill foraging activity carried out by Jeffrey Miner and Roy Stein of the Ohio Fish and Wildlife Research Unit, research found that as light levels increased in turbid water, bluegills foraged on increasingly small items. Also, feeding slowed as turbidity increased. But, no matter how turbid the water, bluegills were able to forage successfully at the highest light levels. In other words, affirming what we already knew, that panfish in turbid water feed best during the middle of the day, regardless of time of year.
William Walton of the University of Maryland reports that the visual resolution of sunfish improves with increasing body size. As sunfish grew from 10 to 38 mm, their MLD increased more than fivefold, due to physiological changes in the eye including the distance between cones in the retina and the location of the pupil relative to the lens center. Apparently, bluegills and sunfish begin their lives nearsighted -- able to focus on tiny objects up close. As they grow, they become increasingly farsighted, better able to react to larger items farther away. This is good news for fishermen.
When it comes to ratios between eye size and body size, crappies are king. They have some of the biggest eyes per inch of body length in the freshwater world. This suggests how important vision is to both black and white crappies. In the world of fish, intense predation stress tends to shape animals to fit their environment. Crappies use this adaptive advantage to feed successfully at night. Their large eyes gather more available light than the tiny eyes of baitfish during the dark hours, giving crappies a distinct advantage at night.
This is helpful when describing the sensory world of the crappie -- including any discussion of vision. Little research has been done on the sensory systems of crappies. Since crappies are closely related to sunfish and bass, much of what we suspect about crappie vision has been assimilated from studies of those other species.
Crappies like to inspect things closely. That fact should temper lure selection on ice. Crappies close in for a better look, and unless involved in some kind of competitive feeding spree, they tend to pause and stare before attacking. A live minnow or a small jig-maggot combo are the most likely items to be taken right away by crappies. Plastic baits must have the right size and profile. But all presentations have to be just right, or crappies tend to reject them.
The forward and upward position of the eyes on a crappie indicate that crappies see best and strike most accurately when positioned slightly below their targets. Crappies orient themselves to prospective forage much as bluegills do, turning and aligning themselves with the target, and approaching it until it's just above their snout. As crappies approach a target, they focus their eyes with specialized muscles that move the lens of the eye back and forth as needed. The lens is retracted for scanning a distant object and extended to ogle things close up, like a zoom lens on a camera. This is another adaptive advantage when trying to accurately feed on items as small as daphnia.
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Though it is probably safe to say that crappies can distinguish chartreuse from yellow or red from pink in clear, shallow water, research indicates that colors disappear at depths around 10 to 15 feet, depending on clarity and light levels. Crappies, like other fish, can switch from a reliance on color-sensitive cones to rods in the retina that detect only black, white, and shades of gray. Crappies apparently see well using their black-white vision, since they feed so extensively after dark in so many lakes, rivers, and reservoirs around the continent.
Panfish in winter tend not to chase things down, the result of a lower metabolism in cold water. It's also possible that the increased use of "slow" muscle tissue in winter makes it more difficult for panfish to focus on or even see things that are moving too fast, which is probably why that pause between jiggles tends to be the most effective trigger so many days on ice.
When a panfish coasts up close and gets personal with a jig, subtle movements prove deadly most -- but not all -- the time. The slow quiver of a tapering plastic tail or the lazy undulations of a live grub or maggot on a jig held still make such a difference some days that it's difficult to doubt that panfish see that type of movement very well. Of course, scent comes into play, too. But it's often the live grubs and maggots that work best, as opposed to dead, motionless baits.
Is color important? We know panfish have the right equipment in the structure of their eyes to see color, and some laboratory tests seem to prove they can learn to react to different colors by consistently striking the right color target -- the one that emits food. From personal experience, I feel convinced that color makes little difference much of the time. Then we have days when certain colored maggots seem to work far better than others. Eurolarvae (maggots) come in many shades, from a natural cream to red, yellow, blue, green, and orange. Some days, I swear the red ones work best, other days, the green ones. Or could be I'm imagining this.
Similarly, I find that, sometimes, color makes a difference with plastic tails. My general rule of thumb for plastics is to start with the colors that traditionally work on that body of water, and if things aren't going well, I switch to the other end of the spectrum. If white is usually the hot color, I might try black, or switch from yellow to purple, or orange to brown. Usually panfish just have to see it to want it, if it has the right size, shape, and action. So, not always knowing what background you're trying to contrast the color against, crossing to the other side of the color spectrum and going from there is a somewhat logical choice. And contrast is the main issue, not color -- especially since deep snow, thick ice, and 15 feet or more of water filter out all the wave lengths of color from light that penetrates that deep, leaving only white. Basin fish, most of the winter, probably see only black, white, and various shades of grey.
Realism is a big thing these days with jigs, plastics, and lures of all kinds. Can panfish see well enough for realistic "fish head" jigs or holographic plastics to make a big difference?
Nah. Probably. Who knows? It's getting too complicated. Put a camera down there and look at your offering. How realistic does it look? And, since your buddy over there is catching crappies on a 1940 version of a marabou jig with the feathers bent in every direction but the right way, do you really care? (Psst. Hey, buddy. What color marabou is that?)