We examined the effects of an aquatic herbicide (Aquathol K) applied prior to largemouth bass spawning to reduce the exotic submersed macrophyte hydrilla (Hydrilla verticillata) and promote establishment of native submersed plants on largemouth bass (Micropterus salmoides) population metrics. Density and biomass of adult (>250 mm) largemouth bass were determined between 2000 and 2003 using a catch-depletion technique in a cove that had been periodically treated with herbicides. Also, catch-per-effort for both number and weight were compared in 2002-2003 between a treated and untreated hydrilla-infested cove. In the cove where catch-depletions were conducted, herbicide applications reduced hydrilla between 2000-2003 and abundance of native plants increased. Coincident with these changes, largemouth bass density and biomass increased 50% to 120%. Over time, the size of fish captured increased in this cove, but temporal changes in relative weight were not evident. In another cove treated with herbicides, native plant abundance was maintained but did not increase, hydrilla was the dominant plant, and catch-per-effort for number and weight was about twice as great than in an untreated cove (100% hydrilla coverage). No differences in size distributions or relative weight were observed between the treated and untreated coves. The application of Aquathol K to coves 2 to 3 months prior to largemouth bass spawning and periodic treatments after spawning was associated with either neutral or positive impacts on population metrics and also resulted in maintenance or an increase in native submersed plants.
