TEMPORAL AND SPATIAL-DISTRIBUTION OF PELAGIC AGE-O FISH IN LAKE MENDOTA, WISCONSIN

Age-0 yellow perch Perca flavescens, sunfish Lepomis spp., black crappies Pomoxis nigromaculatus, and freshwater drums Aplodinotus grunniens had pelagic life history phases in Lake Mendota in 1988, 1989, and 1990, as determined hy purse-seine sampling., The duration of the pelagic phase varied from 3 to 7 weeks and differed between species and in some cases between years within species. Age-0 yellow perch were numerically dominant through most of June and as summer progressed were replaced sequentially by black crappies, freshwater drums, and Lepomis spp. By August, the pelagic community of age-0 fish was numerically dominated by Lepomis spp. This temporal succession of taxa was consistent among years. although the absolute and relative abundance of taxa differed between years. Most species were distributed across the surface of the lake early in their pelagic phase, became relatively more abundant near shore later in their pelagic phase, and then disappeared from the pelagic zone. Other published studies have demonstrated that age-0 fish migrated into the littoral zone of Lake Mendota after their pelagic residence. Variability in density of age-0 yellow perch among replicate sites within depth strata was high, with coefficients of variation ranging from 48 to 154%. The mean-to-variance relationship indicated that the age-0 yellow perch were aggregated. There were significant differences in the density of age-0 yellow perch among years but not among depth strata within years, The purse seine was our preferred gear because it has been shown to catch a wider range of sizes of age-0 fish than most other sampling gear. Therefore. we believe that the temporal and spatial patterns He describe during the pelagic life history phase of age-0 fish in Lake Mendota is more accurate than those described in other studies because our data include a better representation of the larger size-classes of age-0 fish.