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

Age-0 yellow perch Perca flavescens, sunfish Lepomis spp., black crapp ies Pomoxis nigromaculatus, and freshwater drums Aplodinotus grunniens had pelagic life history phases in Lake Mendota in 1988, 1989, and 19 90, as determined hy purse-seine sampling., The duration of the pelagi c phase varied from 3 to 7 weeks and differed between species and in s ome cases between years within species. Age-0 yellow perch were numeri cally dominant through most of June and as summer progressed were repl aced sequentially by black crappies, freshwater drums, and Lepomis spp . By August, the pelagic community of age-0 fish was numerically domin ated by Lepomis spp. This temporal succession of taxa was consistent a mong years. although the absolute and relative abundance of taxa diffe red between years. Most species were distributed across the surface of the lake early in their pelagic phase, became relatively more abundan t near shore later in their pelagic phase, and then disappeared from t he pelagic zone. Other published studies have demonstrated that age-0 fish migrated into the littoral zone of Lake Mendota after their pelag ic residence. Variability in density of age-0 yellow perch among repli cate sites within depth strata was high, with coefficients of variatio n ranging from 48 to 154%. The mean-to-variance relationship indicated that the age-0 yellow perch were aggregated. There were significant d ifferences in the density of age-0 yellow perch among years but not am ong 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 fis h than most other sampling gear. Therefore. we believe that the tempor al and spatial patterns He describe during the pelagic life history ph ase of age-0 fish in Lake Mendota is more accurate than those describe d in other studies because our data include a better representation of the larger size-classes of age-0 fish.