Crappie, often called sac-a-lait in south Louisiana and white perch in north Louisiana, are a very popular freshwater gamefish in much of the United States. Wherever they are found, crappie populations seem to fluctuate noticeably, with good catches some years followed by years of very poor catches. In Louisiana, this cycle seems to be more common in manmade lakes and reservoirs than in rivers, the Atchafalaya Basin, or in freshwater marshes.

But even in these areas a population cycle may be noted. Biologists in Iowa have attempted to determine if environmental conditions may explain some of the variation. They towed a very small mesh net in 11,000-acre Rathbun Lake and compared their catches of larval (newly hatched) crappie against lake water levels, water clarity, temperature, wind, and bottom firmness. Like many fish after hatching, larval crappie are nearly free-floating in the water until they grow enough to swim well.

The results of this investigation were very interesting. The two main environmental factors affecting the number of larval crappie were water levels and water clarity. Almost without exception, high water levels in the lake during the spawning period resulted in high numbers of larval crappie. The only exceptions to this relationship were in years of low clarity (muddy) water. Larval crappie were never found when waters were very muddy during spawning season. Based on previous research, biologists felt that adult crappie abandoned their nests when muddy water created low light conditions on the bottom. They did note that actual suffocation of the eggs may also have occurred.

Temperature was an important, but not overriding factor. Crappie begin spawning when water temperatures reach 61 degrees F. A gradual steady temperature rise, with few ups and downs during the spawning season seemed to produce the most spawning success. The rate of temperature rise did not seem to influence the length of the spawning season, which lasted between 27 and 47 days during the 9 year study.

Wind played a small role in catches of larval crappie. Larger catches always occurred under low wind conditions, but many poor catches were also taken under low wind conditions. High catches never occurred under high wind conditions. This may be due to nest destruction in shallow spawning waters by fetch (wind-produced waves).

The final factor studied was firmness of the lake bottom. While it was a minor factor in larval crappie production, areas with very soft or very hard bottoms did seem to produce less larvae. Other studies have indicated that crappie prefer to spawn on hard clay, usually near some sort of water plants.

During the 9 years of the study, greatest catches of adult crappie by fishermen were made 2 to 4 years after a year of high larval crappie numbers.

Source: Mitzner, Larry. 1991. Effect of Environmental Variables on Crappie Young, Year Class Strength, and the Sport Fishery. North American Journal of Fisheries Management 11:434-542.