Managing Macrophytes to Improve Fish Growth: A Multi-lake Experiment

Abstract

Macrophyte harvesting often has been suggested as a way to improve fish growth and size structure in lakes with high densities of submergent macrophytes and stunted fish populations. However, previous experimental tests have provided no clear consensus on whether the technique works for management. We conducted a series of whole-lake manipulations to test the effects of macrophyte removal on growth of bluegill and largemouth bass. We selected four lakes in southern and central Wisconsin for experimental manipulation and nine others for controls. In August 1994, we removed macrophytes from approximately 20% of the littoral zone by cutting a series of evenly spaced, deep channels throughout each treatment lake. In the first year after manipulation, we observed substantially increased growth rates of some age classes of both bluegill and largemouth bass in treatment lakes relative to controls. Growth rates of other age classes were less responsive to manipulation. We observed increased bluegill and largemouth bass growth despite rapid regrowth of macrophytes in our treatment lakes. By May 1996, fewer than 25% of the channels remained. Our results suggest that harvesting macrophytes in a series of deep channels may be a valuable tool for integrated management of fish and macrophytes.