Each autumn in Minnesota, while many sportsman are concentrating on the hunting seasons, fisherman experience some of their best, and worst, results.
The lakes themselves are the reason for these seemingly random changes as they undergo a natural process called "turnover."
During the summer and winter months, the lake water is separated into 3 distinct levels from top to bottom. The water closest to the surface is the warmest, while deeper in the lake is typically much cooler.
The water where these two meet, called the thermocline, contains the highest levels of oxygen, which holds the largest numbers of fish.
During the spring and summer fishing months, anglers follow the fish patterns through the thermocline, as they feed on smaller fish and other organisms that concentrate there.
Every fall, as the water cools with the air temperature, it will reach a point where all three levels are equal in temperature. This happens at about 39 degrees.
Once the upper layer cools beyond that, the deeper water, which is less affected by the air temperature, will rise and the surface water will sink, flipping the natural layers.
When this occurs, the water layers blend and oxygen is no longer condensed in the thermocline, allowing fish to roam much further and not adhere to normal patterns. This usually triggers heavy feeding from the fish.
While heavy feeding is great for anglers, the fish now have freedom to roam wherever they want to go. This makes locating them very difficult and often frustrating for fishermen.
Today’s fishermen are often armed with sophisticated equipment like sonar and GPS that helps in finding the fish. Advanced lures and techniques also add to success by further enticing the fish to bite.
Not long ago it was quite uncommon to see someone fishing after labor day weekend. This may still be the general rule, but now it is not out of the ordinary to see fishing boats out right until ice begins forming.
The timing of the turnover is difficult to predict with changing weather patterns from year to year. As temperatures continue to cool, turnover should take place in the Bemidji area very soon.
Fish have a way of sensing the turnover better than humans, and their behavior will give fishermen a clue as to what is happening below the surface.
Fishing right before turnover and after the high activity period is often slow, as fish feed less due to the change in environment.
Anglers experiencing this slow period usually take this time to winterize the boat for the year, and dig out the ice fishing gear.
Some of the best fishing comes shortly after, as first ice hits the lakes in November or early December.
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