Exploring zooplankton changes in southern Lake Michigan: Implications for yellow perch recruitment

Recruitment of fishes frequently depends in part on availability of appropriate densities and sizes of zooplankton prey. In Lake Michigan, yellow perch (Perca flavescens) have experienced poor recruitment since 1989, although the mechanisms driving this poor recruitment have not been identified. To explore the possible influence of zooplankton density available for yellow perch larvae shortly after hatching on eventual recruitment success of age-0 yellow perch, we examined patterns of nearshore zooplankton and age-0 yellow perch relative abundance in southwestern Lake Michigan during June 19881990 and 1996-1998. Zooplankton density, mean size, and biomass that were available to newly hatched yellow perch larvae in June declined from the late 1980s to the late 1990s, suggesting that one or more of these declines may contribute to the current reduced rate of yellow perch recruitment seen in southwestern Lake Michigan. A strong positive linear relationship existed between the density of zooplankton present during June, the time when first-feeding larvae appear, and CPUE of age-0 yellow perch in a given year. A laboratory experiment revealed that more zooplankton does increase larval yellow perch survival, supporting the field pattern. Therefore, zooplankton availability for larvae can be an important determinant of yellow perch recruitment success in Lake Michigan and should be considered in addition to other mechanisms when evaluating the factors regulating recruitment of this species.