Effects of Aquatic Plant Manipulation on Angling and Fish in Fish Lake, Dane County, Wisconsin

Abstract

Slow-growing centrarchid populations are a common management problem in heavily vegetated lakes. Typically, vegetation is managed to increase recreational opportunities, with little regard to the effects it may have on fish populations or associated angling catch rates. This thesis evaluates largemouth bass, bluegill, and angling responses to a plant reduction at a whole-lake scale, and provides guidance about the link between vegetation management and fish management. A plant manipulation was initiated in 1994, using an experimental close-cut mechanical harvester as a fishery mangement tool to increase macrophyte bed edge habitat, and increase the growth of predator and prey fish populations. Measuring direct and indirect effects of the manipulation were important objectives, thus I compared largemouth bass and bluegill populations, and angling dynamics between pre- and post-treatment years. A reduction in vegetation increased the growth and survival of largemouth bass. This led to increased recruitment of largemouth bass to larger size, thereby increasing the population size structure. Effects on the bluegill population were less consistent. Following macrophyte reduction, bluegill growth declined or remained similar as fish aged. Yet, increased bluegill survival led to improved population size structure. I conclude that increased survival of largemouth bass and bluegill was the result of a decline in natural mortality. The plant manipulation increased angling opportunities, and was associated with increased angler pressure. I conclude that a decline in summer angling catch rates of largemouth bass were caused by a combination of increased angler effort, increased availability of bluegill, and increased available cruising habitat for largemouth bass. Summer angling catch rates of bluegill also declined with increased angler pressure. Reduced vegetation was associated with sharp declines in natural mortality of fish that left more fish available for anglers, and coincided with much higher fishing mortality of bluegill. Anglers caught more large bluegill, and the increased fishing mortality after the plant manipulation did not appear to reduce bluegill population size structure. This field research indicates that a reduction in plant biomass, and increase in vegetated edge habitat can significantly increase the growth, survival and size structure of largemouth bass and bluegill populations, and produce more angling opportunities.