Assessing the Utility of Otolith Chemistry for Management of Six Freshwater Fishes from a River-Reservoir System

Floodplain habitats often function as spawning, rearing, foraging, and refuge environments for riverine fishes. Although floodplain habitats are important for fish production and recruitment, their natal contributions may vary by species, a topic that has not been thoroughly investigated in large floodplain rivers. We evaluated the natal contributions of floodplain habitats to populations of six socioeconomically important sport fishes in Lake Sharpe, South Dakota, using otolith chemistry. Water samples and age-0 and adult fishes were sampled from five habitat types (canal, embayment, main channel, stilling basin, tributary). Age-0 fishes were classified to known natal habitats with 83% mean accuracy based on otolith Ba:Ca and Sr:Ca signatures, with 89% mean accuracy for Bluegill Lepomis macrochirus (89%), crappies Pomoxis spp. (88%), and Largemouth Bass Micropterus salmoides (91%). Floodplain habitats had substantial natal contributions to Bluegill (50%) and crappie (35%) populations. Despite spanning only 0.8% of Lake Sharpe by surface area, a specific floodplain habitat (Hipple Lake) contributed 15% of Largemouth Bass to the Lake Sharpe population19 times greater than expected under a linear contribution-area relationship. Floodplain habitats had smaller natal contributions (0-5%) for reservoir-oriented species such as Smallmouth Bass M. dolomieu and White Bass Morone chrysops than for centrarchids and Yellow Perch Perca flavescens. Given that floodplain habitats in Lake Sharpe, particularly Hipple Lake, are disproportionately important for sport fish populations relative to their size, maintaining river-floodplain connectivity is crucial for effective fisheries management. Otolith chemistry is a tool for sport fish management in Lake Sharpe as it reveals habitat-specific natal contributions of diverse species and can be used to prioritize areas for floodplain protection and rehabilitation, harvest regulations, stock enhancement, and other fisheries management activities.