Response of a Reservoir Fish Community to Aquatic Vegetation Removal

Abstract

Over 3,600 hectares of submersed aquatic vegetation in Lake Conroe, Texas, were eliminated 1 year after 270,000 grass carp Ctenopharyngodon idella were stocked in 1981–1982. Seventeen fish species were commonly collected in cove rotenone samples and the biomasses of eight species declined (P ≤ 0.10) after vegetation removal. The most notable declines were observed for several small, phytophilic Lepomis spp., for bluegill Lepomis macrochirus, and for crappie Pomoxis spp. Biomass of largemouth bass Micropterus salmoides did not decline (P = 0. 12) but the density of age-1 and older fish did decline (P = 0.02). Biomass and density of two cyprinid species and channel catfish Ictalurus punctatus increased. Although biomass of longear sunfish Lepomis megalotis did not increase (P = 0.11), mean size declined and density increased an order of magnitude (P = 0.02). Density of threadfin shad Dorosoma petenense increased nearly fivefold after vegetation removal, coincident with a decline in mean size; however, variability was high and the difference could not be declared significant. Biomass of gizzard shad D. cepedianum fluctuated due to inconsistent year-class production that was not directly related to vegetation coverage, Seining revealed that populations of three cyprinodontid species, bantam sunfish Lepomis symmetricus, and brook silversides Labidesthes sicculus collapsed following vegetation removal, whereas catches of inland silversides Menidia beryllina and threadfin shad increased significantly. Gillnetting revealed that large year-classes were produced by yellow bass Morone chrysops and white bass M. mississippiensis following vegetation removal. Although abundance of white crappie Pomoxis annularis declined in offshore regions sampled by gill nets, catches of black crappie P. nigromaculatus were similar before and after vegetation removal. No change in abundance or structure over this 7-year study could be detected for at least 10 populations. The original largemouth bass-crappie-hybrid striped bass (Morone chrysops × M. saxatilis) fishery was replaced by a channel catfish-white bass-hybrid striped bass-largemouth bass-black crappie fishery after vegetation removal. The observed response of many species to vegetation removal could be predicted given published information, but mechanisms governing the dynamics of several important species were unclear.