Quasi-cycles in crappie populations are forced by interactions among population characteristics and environment

Crappie (Pomoxis spp.) populations have been characterized as cyclic, with strong year-classes recurring at 2- to 4-year intervals. We evaluated the p otential for cyclic trends in crappie populations using a population model that included a density-dependent stock recruitment function and random env ironmental variation. Slow, medium, and fast growth were simulated over 100 years. The model predicted highly variable recruitment that was strongly i nfluenced by environmental fluctuation at low and intermediate stock densit ies. At high stock density, recruitment was low, even if environmental cond itions were favorable. Significant quasi-cycles occurred, but they were not sustained throughout the time series due to random environmental fluctuati on. Quasi-cycles occurred because intermediate stock density and favorable environmental conditions occasionally combined to produce a very strong yea r-class that greatly increased stock density in the following 1-3 years and produced low recruitment, even if environmental conditions were favorable. Empirical data from 32 years of sampling age-0 crappies at Ross Barnett Re servoir showed trends similar to the simulated fluctuations. We conclude th at crappie populations likely do not exhibit true cycles but may show quasi -cycles as a result of the interaction between random fluctuations in envir onment and density-dependent mechanisms. The frequency of such quasi-cycles may be enhanced by rapid growth and high exploitation.