THE IMPACT OF SUBMERGED MACROPHYTES ON LARGEMOUTH BASS AND BLUEGILLS

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Abstract
Underwater macrophytes can influence fish diet and growth by restricting access inshore. The movements of largemouth bass (Microptems salmoides) and biuegills (Lepomis macrochirus) were followed in a shallow Wisconsin impoundment nearly one-half covered with potamogetons and other macrophytes. Plant density averaged 130–200 g/m2(dry weight) from May through August during the six-year study. Fish activity was observed from a still boat or by diving. Stomach samples of fishes were obtained on 55 dates by boom shocking. Submerged macrophytes at a density above 90 g/m2functioned as a screen to selectively restrict fish movements. Bass and bluegills under age III were mostly confined to plant beds, where they grazed chironomid larvae and other aquatic insects on the plants and lake bottom. Bluegills shifted to zooplankton and finally plant tissue as summer progressed, while bass turned increasingly to fish as prey. Older bass had difficulty in penetrating the plant beds until openings appeared from plant decay or were created by a mechanical harvester. Slow growth of bass after age II was also reported in other Midwestern lakes with dense vegetation and is attributed to their difficulty in foraging on young fishes inshore. Selectively channelizing macrophyte beds with bottom screens or a mechanical harvester can be an effective management strategy to enhance fish growth in densely-planted lakes.