Transition Zones

Once a lake stabilizes, crappies can find oxygenated water on deeper flats that were, just weeks ago, out of reach. Down on those flats they find fields of invertebrates that may have remained uncropped by any kind of fish life for several months. The emergence of new feeding grounds attracts various species of baitfish, which in turn draw crappies—all predictably structure-oriented. As pointed out earlier, a variety of substrates coming together in one area offers a more diverse selection of invertebrates—one of the primary reasons “transition zones,” where hard bottom meets soft, attract a variety of species in fall, including walleyes, bass, perch, and bluegills, as well as crappies.

Hard-to-soft transition zones ring the basins of most lakes. Basins are another piece to the puzzle, offering the best winter habitat for crappies in most natural lakes. As the water continues to cool in fall, crappies move closer and closer to areas of the greatest environmental stability. Needs for stable temperatures, stable ph factors, stable food supplies, and protection from wind-driven currents begin to corral the fish in predictable locations. Crappies are not well equipped to handle benthic depths of 80 feet or greater, so they tend to prefer enclosed basins of moderate depth—basins no deeper than about 50 feet. In many lakes, they concentrate in basins found in bays. In other lakes, they find large depressions on otherwise shallow flats. These basins and depressions tend to max out between 20 and 45 feet in depth in most cases. However, some lakes have no such basin areas and crappies are forced to find flats in that 20- to 45-foot depth range that borders much greater depths.

Odds are good that the bottom of an enclosed basin or of a large depression on a flat is soft—made up of muck, silt, or some composite of other soft substrates. Structural elements that hold crappies most of the year—points, humps, islands, rockpiles—tend to be composed of some combination of bedrock and/or broken rock blending into gravel, then sand, clay, or similar “hard” substrates. Where these substrates blend into the softer types carpeting the basin itself, crappies can concentrate. But it’s a linear concentration, spread out along a narrow, snaking transition zone between hard and soft bottom types.

Bottom transition zones can be located quite easily, in most cases, with sonar. Hard bottom produces a “hard” reading on a depthfinder screen, and soft bottom produces a thinner, more diffuse signal. The sound emitted by the transducer on a depthfinder doesn’t “bounce” off muck very well. Much of the energy of the signal is absorbed. So, with the gain turned up on a sonar unit, it’s possible to visually see (and place markers along) the demarcation between hard and soft bottom types. An underwater camera can further clarify precisely what types of bottom are actually coming together below the boat. It can be important, when trying to develop angling patterns for crappies, to know whether they’re holding on clay or sand, muck or gravel, and so on.

Bottom transition zones around these basins and flats can exist anywhere from 8 to 70 feet down, or even deeper. More commonly, the transition zone (which is only a few feet wide, in most cases) occurs somewhere between depths of 15 to 40 feet. It’s common, too, to find transition zones along edges where the bottom begins to flatten out. Where the breaks (drop-offs) leading down from structures crappies use in summer—such as main-lake humps, shoreline points, islands, and rockpiles—meet the softer substrates of a basin, they become principle holding zones. Crappies can become structure-oriented, and often hold so close to bottom they cannot be marked with sonar—especially when active along transition lines. Active fish can be right on bottom when feeding, while inactive crappies may suspend within 2 to 10 feet of bottom.