The incidence of predation by largemouth bass Micropterus salmoides on fish in Lake Conroe, Texas, was examined over 7 years at two disparate levels of habitat complexity. When areal coverage of submersed vegetation ranged from 39 to 44% of the reservoir's 8,100 hectares, largemouth bass 100 mm and smaller in total length consumed fish infrequently; most did not consume fish until they reached lengths of 140 mm and more, Following the elimination of all submersed vegetation by grass carp Ctenopharyngodon idella, fish were consumed by most largemouth bass 60 mm or longer. The initiation of piscivory at smaller sizes resulted in significantly faster first‐year growth for all largemouth bass year‐classes produced after vegetation removal. Although shifts in the structure of the forage fish community occurred, ample fish prey existed for largemouth bass before and after vegetation removal. The onset of piscivory remained similar for largemouth bass collected along the dam riprap, where vegetation was absent throughout the study. These observations support the hypothesis that habitat complexity, as mediated by vegetation abundance, was the principal factor regulating piscivory by largemouth bass in the littoral zone of Lake Conroe.
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 Mor one 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 (Mor one chrysops x 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.
We counted annul! on otoliths, scales, anal fin rays, and anal fin spines of striped bass Morone saxatilis to determine precision of age estimates from several readers and relative accuracy of the estimates from the different structures. Our principal objective was to determine if estimates from scales, spines, and rays, which can be removed without harming the fish, were similar to those from otoliths. Among-reader variation was similar for spines, scales, and rays, and lowest for otoliths. Variation increased with fish total length (TL) for otolilhs and scales. Age estimates from scales, spines, and rays were usually within 1 year of the otolith age estimate for striped bass shorter than 900 mm TL. However, for striped bass longer than 900 mm TL, estimates from spines and scales were lower than estimates from otoliths by averages of 1.6 and 3.0 years, respectively. Scales, spines, and rays can provide relatively accurate and precise age estimates for striped bass up to about 900 mm TL (age 10 from our samples). For longer fish, the choice of a structure for age determinations should depend on whether the improved accuracy and precision expected from otoliths is worth killing the fish.
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