Predator Density and Size Structure in Different Habitats of Toledo Bend Reservoir, with Implications for Increasing Stocked Largemouth Bass Survival

Texas Parks and Wildlife Department (TPWD) primarily stocks Florida largemouth bass (Micropterus salmoides floridanus; total length range 30 to 46 mm) to influence the genetic composition of existing populations or to supplement limited recruitment. These stockings have altered the genetic composition of largemouth bass populations; however, stockings often result in variable and low contributions to cohort abundance. Potential sources of stocked fish mortality include hauling stress, lack of prey and foraging success, and predation. Previous studies indicate that predation may be the largest immediate source of mortality with estimated losses of over 25% of all stocked fish within 12-h post stocking in a Texas reservoir. This study evaluated community structure, abundance, and size structure of potential predators in five different littoral habitat types including featureless banks, hydrilla (Hydrilla verticillata), timber-hydrilla, timber, and semi-terrestrial cover over an eight-month period. Littoral predator species densities and compositions changed across time, with higher overall densities observed in the spring and fall. Featureless habitats were the most dissimilar with respect to predator abundance. Habitats characterized by hydrilla had the highest largemouth bass densities in the spring and fall, but in summer months, largemouth bass densities were highest in semi-terrestrial habitat types. Spotted bass (M. punctatus), redbreast sunfish (Lepomis auritus), and longear sunfish (L. megalotis) exhibited a preference for featureless habitat types, while redear sunfish (L. microlophus) and spotted gar (Lepisosteus oculatus) preferred habitat dominated by timber. Stocking may be more effective in sites that contain fewer predators that prey on largemouth bass fingerlings at lesser rates or less efficiently as this study indicates that different fish assemblages exists between both habitat types and time.

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