Effects of Mechanical Harvesting of Eurasian Watermilfoil on Largemouth Bass and Bluegill Populations in Fish Lake, Wisconsin

Abstract

We examined changes in populations of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus associated with mechanical plant harvesting in a lake heavily infested with Eurasian watermilfoil Myriophyllum spicatum. In Aug 1994, 18% of the total plant biomass in Fish Lake, Dane County, Wisconsin, was removed in a radial pattern of 2-m-wide channels. Largemouth bass and bluegill abundance, survival, growth, and length frequency were compared between pretreatment (1992–1993) and posttreatment (1995–1996) years. Following vegetation removal, mean abundance of largemouth bass and bluegill did not change significantly, but growth increased for age-2–4 largemouth bass and declined for age-5 largemouth bass and age-4–5 bluegills. Survival increased for age-2, −3, and −5 largemouth bass and age-4–6 bluegills. Population size structure increased for both species. We conclude that removal of Eurasian watermilfoil may increase growth and survival of some age-groups of centrarchid populations without altering the abundance of either species. However, this study lacked replication and control that is needed to separate effects of plant harvesting from effects of other biotic and abiotic factors.