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Fishing the Well Curve

by Joseph D. Cornwall


Originally Published in Country Anglin' Outdoor Guide
March/April 2005



Previously, the "bell curve" defined normal statistical distribution, and it became a fundamental law of natural science, a cornerstone of statistics. Recently, several economic and social phenomena seem to be following a different pattern. Instead of being high in the center and low on the sides, this new distribution is "bi-modal", low in the center and high on the sides. So, it's called "the well curve".
                                                               - Jim Pinto

What could statistical distribution, bell curves and inverse bell curves possibly have to do with improving one’s fishing skills? That is the question I would have asked last year. After letting a few observations and some thoughts on seasonality brew in the back of my mind for a good, long while, I’ve determined that the answer is “it has everything to do with successful angling!” The inverse bell curve describes almost perfectly the type and size of bait the astute angler should imitate to maximize on-water success over the course of the year. Of course leader length, diameter, and fly line weight are directly proportional to fly size, so the well curve also describes the changes in tackle we should consider as the season progresses.

I’ve heard the advice that in the spring one needs to fish smaller, colorful artificials because the fish’s metabolism is slower and they respond better to smaller baits in cool water. In the same vein, I’ve heard advice to fish larger flies in the summer because the fish’s metabolism will have them hunting larger meals more frequently. To muck things up even a little more, the same advice given to a fly fisher and a spin fisher will be manifest significantly different imitations – small for a fellow with a bait- casting rod and spinnerbait is ENORMOUS to a freshwater fly fisherman! Small to a fly fisherman may be almost microscopic to that same hardware aficionado! There has to be a better way of thinking about, and understanding, proper imitation guidelines. Enter the well curve.

Let’s look at typical fodder size over the course of a year from a fish’s point-of-view. Starting in January we will see that there are no fry or immature baitfish. The little guys just don’t have the energy reserves and hardiness to make it through a rough winter. Young-of-the-year must achieve a certain minimal size, proportional to the species, to be able to handle the rigors of the cold season; this is the immutable law of nature. Baitfish, aquatic insects and decapods all follow this plan. Because in January all baitfish and young-of-the-year game fish and rough-fish will have reached this critical size, it is important that we select a fly or artificial that is appropriately imitative. Immature carp will be three to four inches long. Immature Johnny darters will be one-and-one-half to two inches long. Gizzard shad will be mature, and two to four inches long. Mayflies will be on their last instars; implying that hendrickson nymphs will be 7mm (about size 12 or 14). Crayfish (those accessible in during this, a normal period of aestivation) will be two to three inches long. And so the list continues.

Imitation of a three-inch baitfish with a fly typically requires a size 4 or larger hook. Imitation of a four or five inch baitfish may require a 2/0 hook. Excellent choices for imitation at this time of year include young carp, stonecats and mature shiners or chubs. These are significantly larger than the size 8 and 10 flies many anglers with a classic “trout” perspective will consider a big fly! In January, you’re better off leaving that 4wt rod at home and grabbing for something with the horsepower to propel large streamers and respectable insect imitations to the target, often accompanied by splitshot and extra weight to counteract the affects of high, fast flows.

Most species don’t begin spawning until after spring equinox, the earliest spawners providing the first wave of fry sometime in April. Insects will become more numerous and active with the warming water and lengthening daylight, meaning the average size of food in the daily natural drift will begin to decrease, following the well curve shape into the coming spring. By the time the flowers are in full bloom there may be as much or more active biomass below the one-inch limit as there is above! The dichotomy is that the truly minute are often too small to be a reliable food source, so the focus shifts to species that are smaller and more temperature sensitive overall. For late spring and early summer, focus on imitating mature Johnny darters, young male crayfish, dace and shad. Fly sizes are now a reasonable one-and-a-half to two inches long and can be effectively presented on size 4, 6 and 8 hooks. Mayflies, caddisflies and stoneflies will all be at their largest as they emerge or prepare to emerge; imitations in sizes 10, 12 and 14 will prove most effective.

By June, panfish are on the beds and most gamefish are completing their spawning activities. The amount of truly small food sources multiplies exponentially as the season progresses, reaching its peak in July with the proliferation of juvenile, young-of-the-year crayfish, fry of nearly every resident species, and recently hatched immature nymphs. Tiny, young bluegill might be one-half inch long. Little crayfish will regularly molt, growing a bit each time. The shallows are alive! When the fireworks of July ring out- fly size might span a range from tiny size 14 and 16 crayfish and micro-streamer imitations to six-inch long creek chubs. If your goal is to effectively imitate the most accessible meal, you’re likely fishing a size 10 or 12 streamer or maybe a small terrestrial insect imitation.

When summer begins to give way to autumn we see all river residents focusing on caloric intake. They need to “bulk up” to make it through the coming cold season. Mature crayfish molt and mate. Young- but full sized- shad begin migrations to the larger, deeper waters they will call home. Fly sizes begin to climb, from small in September to big and meaty by December. When the holidays are again upon us we are back to fishing big flies on big rods, hopefully for big fish!

Let the well curve guide you this season. Ask yourself, how big is the food going to be today. What species of food might my targeted trophy have its eyes on. What is that food doing, and how big is it? Answer those questions and you’ll find yourself tossing a more effective selection of flies over a more receptive population of gamesters. Till next time… tight lines and soft water!


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