S.M Hanson
Michigan State Univeristy
East Lansing, MI


ABSTRACT

Eurasian watermilfoil (hereafter EWM) is thought to alter largemouth bass-bluegill interactions in systems it invades by reducing bass mobility and encounter rates with bluegill. Thus, bass foraging ability on bluegill may be reduced potentially resulting in poor bass growth. The selectivity of aquatic herbicide SONAR for EWM, allowed me to evaluate the effects of whole-lake EWM reductions on largemouth bass diet and growth. Specifically, I compared the diet and growth of largemouth bass in lakes treated with SONAR in 1997 to that of reference lakes during pre- and post-treatment time periods. Analysis of bass diets from a subset of the study lakes in 1999 indicated there were no differences in the contribution of bluegill to bass diets between treatment and reference lakes. However, ass growth increased in the treatment lake relative to the reference lakes post treatment. The increase in bass growth was limited to bass <200 mm and the projected length at age of bass in the treatment lakes suggested the effect of increased would diminish as bass grow to reach a legal capture size. My results suggest EWM negatively affects growth of bass <200 mm and its selective reduction using SONAR herbicide is an effective tool for aquatic plant and fisheries management.