Will muddy water this year affect your fishing next year?
Successful anglers are continually aware of how environmental conditions affect fish, but their focus usually is on the adults of the species they are targeting.
Environmental conditions affect the young fish, too. Understanding the effects of environmental conditions on young crappie is especially important because abundance of crappie year-classes varies widely over time.
In many lakes, turbidity fluctuates widely within and between years. Might turbidity affect recruitment of one of the Magnolia State’s most popular sportfish? A study by Illinois Natural History Survey researchers provides insights.
Young black and white crappie were collected with seines from hatchery ponds and transferred to laboratory tanks. Young crappie were collected at several times after spawning to allow testing for the effects of turbidity on different life stages.
In the laboratory, fish were held in clear water at 72° F and fed Daphnia, Chaoborus and Chironomus larvae to acclimate to laboratory conditions. Daphnia are relatively large zooplankton that live in the water column. Chaoborus, also known as phantom midge larvae, have clear bodies; they spend much of their time living on the bottom but make frequent migrations into the water column. Chironomus are dark-bodied midge larvae that live in the bottom sediments. All are foods commonly eaten by young crappie.
Fish were transferred to tanks and offered known amounts of each forage type at three levels of turbidity that corresponded to visibility of 14 inches (clear water, no turbidity), 12 inches (moderate turbidity), and 9 inches (high turbidity).
The amount, measured as weight, of Daphnia consumed by white crappie did not differ among turbidity levels. Black crappie ate the least in clear water and greater and similar amounts in moderate and high turbidity.
Young fish that feed on plankton are known to be size selective, generally tending to select the larger zooplankton that contain more energy. White crappie selected the largest Daphnia in clear water and smaller Daphnia in moderate and high-turbidity water. Black crappie had the opposite trend, selecting the smallest Daphnia in clear water and larger Daphnia in moderate- and high-turbidity water. Although trends were different, size selection for Daphnia was similar for black and white crappies in waters with moderate and high turbidity.
When provided with all three prey species, both black and white crappies selected Chaoborus at all turbidity levels. Daphnia and Chironomus were either avoided or neutrally selected; that is, they were neither selected for nor avoided.
Most important, turbidity did not affect the mass of food or energy consumed by either species. However, black crappie consistently consumed more food and energy than white crappie at all turbidity levels.
Some of the results of this experiment are hard to reconcile with field observations. Black crappie tend to be more abundant in clear-water systems, and white crappie appear more tolerant of turbid water. Yet, black crappie consumed more food and energy at all levels of turbidity than white crappie. The only difference between black and white crappie feeding was the lesser amount and selection of smaller of Daphnia in clear water by black crappie, a result unlikely to account for black crappie tending to be more abundant in clear-water and less abundant in turbid-water lakes and reservoirs.
One important variable that can affect foraging of young crappie is predation. For young crappie, feeding is a continual trade-off between feeding where food is abundant and avoiding areas where predation risks are high. The outcome of these experiments may have been different if predators were present, but the experiments are informative in that turbidity, alone, has little effect on crappie food intake.
What factor or factors determine the dominance of black crappie or white crappie in a lake or reservoir are yet to be determined; but for anglers who fish in systems with widely varying turbidity, it is good to know that turbidity does not suppress food intake of young crappies and is unlikely, therefore, to affect recruitment after spawning.