Distribution of littoral fishes in structurally complex macrophytes

Abstract

By considering patchiness in the littoral vegetation, we were able to distinguish within-lake distributions among species and between young-of-the-year and yearling-and-older fishes. We characterized the macrophytes in Lake Mendota, Wisconsin, along transects using rake grabs to estimate species diversity and sonar charts to estimate the patchiness at 1-m intervals. We discerned two distinct littoral fish assemblages, one characterized by rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu) in unvegetated areas and another by a diverse assemblage in vegetated areas. Patchiness of macrophytes, not simply abundance, determined variations in the specific structure of the fish assemblage: e.g., yellow perch (Perca flavescens) were more dominant and abundant where vegetation was species rich and structurally complex as well as abundant. Young-of-the-year and yearling-and-older fishes differed in their distribution patterns: e.g., age 0 bluegill (Lepomis macrochirus) were more abundant where Eurasian watermilfoil was abundant and patchy and yearling-and-older bluegill where vegetation was more dense and species rich. Furthermore, yearling-and-older black bullhead (Ameiurus melas) and brown bullhead (Ameiurus nebulosus) were more common in patchy macrophyte beds than in species-rich vegetation. The largest catches of age 0 white bass (Morone chrysops) occurred at sites with sandy shallow beaches and patchy milfoil beds farther offshore. These patterns were discerned because we assessed macrophyte structural complexity at multiple scales and we separated young-of-the-year from older fishes.