Thermocline breakup signals return to the shallows for crappie

In advance of a birthday, in honor of a fishing merit badge earned, and because he just plain wanted to go fishing, Ole Miss Market Professor Dr. Matthew Shaner booked a guided crappie fishing trip with Mississippi fishing guide service Barton Outfitters.

Matt brought along his son, 11-year-old Boy Scout Gavyn. As the pair were walking down the ramp, Gavin asked his guide, Oxford resident Aaron Barton to remind him how to tie several knots he had learned in scouts (neither of which Barton had a clue how to tie). The first of a hundred good questions, laughs, and smiles, the group was underway before dawn.

The father/son team trolled minnows searching for crappie that are now roaming from less than five feet of water to over 30 feet.

“These large Mississippi flood control reservoirs are monomictic, meaning the lake mixing regime process that results in stratification and the development of a thermocline followed by thermocline breakup (commonly known as “turnover”) occurs just once per year,” Barton explained.

A thermocline is thin but distinct layer in a large body of fluid in which temperature changes more rapidly with depth than it does in layers above or below. This phenomena occurs in large North Mississippi reservoirs during the summer as longer days and warmer temperatures heat the very top part of the water column causing it to become less dense. Waves caused by wind and other energy transfer mechanisms causes the water to mix distributing the heat up to 8-14 feet subsurface. This warmer water is constantly agitated and turning over causing it to have a relatively higher oxygen content, whereas the deeper colder water is less subject to these forces. This point where less dense, warmer, more oxygenated water sits atop more dense, colder, less oxygenated water creates essentially a floor or bottom below which crappie are very unlikely to be caught.

Knowing where the thermocline is at any given point on the lake (as it can very from place to place on the same body of water) and in its annual cycle is helpful when crappie fishing. If crappie are hugging the bottom in shallower water (8’-12’) they probably are hovering near the thermocline in deeper water (which could be up to 18’ deep in certain lakes).

If crappie are being caught or are present in extremely shallow (less than 5’ of water) it is an indication that that thermocline has broken up, the lake has turnover and oxygen is more evenly distributed throughout the water column as well as in shallower parts of the lake.

Complex fishing matters such as this, lighter topics such as the presence of alligators, “jellyfish” (bryozoa) and how Matt met his mother were covered. Gavin asked as many questions as he could think of and most were answered truthfully, directly and with amusement.

This particular early October day, indications that turnover had occurred was clear, as many boats could be seen fishing shallow and in the backs of coves. Following suit, baits deployed ranged from minnows fished 6-10 feet deep, followed by diving baits fished twice as deep, with the latter outperforming by a wide margin. Dark colors worked equally as well as lighter or shad patterned colors.

Young G was quick to take instructions, respectful, and a capable angler.

Unfortunately for the fierce competitor in Gavyn, his dad was too.

Both fisherman were neck and neck with an inconclusive livewell full of 12.25” to 13” fish. After Matt pulled a 14.5” toad out, the only question on Gavin’s mind for the rest of the day was if his next fish was bigger than dad’s.

It was a fantastic day of curiosity, camaraderie, crappie and catching. Give us a call and let us help you make the fish happen.

Aaron Barton
Barton Outfitters

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