Reduced river–floodplain connectivity can decrease fisheries production and cause ecological and socioeconomic consequences. In 2011, the largest flood on record in the Missouri River since 1898 nearly eliminated connectivity between an embayment (Hipple Lake) and Lake Sharpe, impeding movement of walleye (Sander vitreus) and a forage fish, gizzard shad (Dorosoma cepedianum). Thus, we used otolith chemistry to quantify Hipple Lake's natal contribution to Lake Sharpe's gizzard shad population and forecast effects of connectivity loss on the reservoir's socioeconomically important walleye fishery. Fish were classified to natal habitats with 79–89% accuracy, with most gizzard shad (64%) hatching in floodplain habitats (i.e., embayments, tributaries, canals, and stilling basins). Hipple Lake contributed 12% of gizzard shad to Lake Sharpe, more than a tributary (4%) and embayment (0%) but less than a canal (27%) and stilling basin (21%). Hipple Lake (178 acres) covers 0.31% of Lake Sharpe (56,884 acres), so its natal contribution is 38 times what would be expected if contribution was linearly related to area. Sediment and water management to maintain connectivity between Lake Sharpe and Hipple Lake and other floodplain habitats is important for continued gizzard shad production and prey supply for the walleye fishery. Otolith chemistry facilitates assessment of gizzard shad natal contributions in different habitats, serving as a fisheries management tool to inform floodplain habitat protection and rehabilitation after floods.

Entrainment of fishes through impoundments is common, and Rainbow Smelt Osmerus mordax, which is the dominant forage fish species in the Missouri River reservoir, Lake Oahe, is frequently entrained through Oahe Dam at low rates. In 2011, the Missouri River endured a flood of a magnitude never before experienced in recorded history. Concerns regarding Rainbow Smelt entrainment were numerous; thus we sought to determine Rainbow Smelt entrainment rates. To evaluate entrainment, we used stationary trawls downstream from each Oahe Dam outlet structure and repeated hydroacoustic sampling above Oahe Dam on Lake Oahe. Trawl sampling estimated that 231 million adult and 433 million age‐0 Rainbow Smelt were entrained during the summer of 2011. Hydroacoustic sampling estimated a loss of 213 million adult and 520 million age‐0 Rainbow Smelt from Lake Oahe. Thus, both gears provided an estimate of Rainbow Smelt loss that was surprisingly similar. Additionally, Rainbow Smelt entrainment rates were substantially higher from 1500 to 2100 hours. This corresponds to the time of day when Rainbow Smelt exhibit a diel migration into the water column likely making them more susceptible to entrainment as they pass by Oahe Dam intake structures. By reducing discharge during this critical time period, entrainment of Rainbow Smelt could be dramatically reduced. Received October 7, 2015; accepted March 14, 2016 Published online July 8, 2016

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 population—19 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.

Gizzard Shad Dorosoma cepedianum, a pelagic detritivore found throughout the USA, are an important prey fish for many sport fish species and are often stocked in an attempt to bolster sport fish growth and condition. To date, there has been little research on how many or at what density prespawn adult Gizzard Shad should be stocked in order to produce a year‐class suitable for sport fish consumption within that year. In Lake Oahe, South Dakota, Gizzard Shad are an important prey resource for Walleyes Sander vitreus and other sport fish when the number of Rainbow Smelt Osmerus mordax is low. However, severe winters in 2009–2011 extirpated the Gizzard Shad population in Lake Oahe (or reduced its abundance to below the detectable limit). Thus, Gizzard Shad were stocked in 2012 and 2013 to improve short‐term prey fish production. During this time, we sought to identify how many or at what density prespawn adult Gizzard Shad need to be stocked in select embayments of Lake Oahe to achieve larval Gizzard Shad production similar to that in years when natural reproduction took place. Although the results were quite variable, we found positive linear relationships between the density of larval Gizzard Shad and the number and density of adult stockings, with the number of adults stocked providing a better indication of later larval production than adult stocking density. In general, stocking 150 prespawn adult Gizzard Shad would produce larval densities ≥5.0 fish/100 m3 in select embayments of a large Midwest reservoir.Received November 8, 2016; accepted February 15, 2017 Published online April 27, 2017

Geology and hydrology are drivers of water chemistry and thus important considerations for fish otolith chemistry research. However, other factors such as species and habitat identity may have predictive ability, enabling selection of appropriate elemental signatures prior to costly, perhaps unnecessary water/age‐0 fish sampling. The goal of this study was to develop a predictive methodology for using species and habitat identity to design efficient otolith chemistry studies. Duplicate water samples and age‐0 fish were collected from 61 sites in 4 Missouri River reservoirs for walleye Sander vitreus and one impoundment (Lake Sharpe, South Dakota) for other fishes (bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, gizzard shad Dorosoma cepedianum, largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, white bass Morone chrysops, white crappie P. annularis, and yellow perch Perca flavescens). Water chemistry (barium:calcium [Ba:Ca], strontium:calcium [Sr:Ca]) was temporally stable, spatially variable, and highly correlated with otolith chemistry for all species except yellow perch. Classification accuracies based on bivariate Ba:Ca and Sr:Ca signatures were high (84% across species) yet varied between floodplain and main‐channel habitats in a species‐specific manner. Thus, to maximize the reliability of otolith chemistry, researchers can use species classifications presented herein to inform habitat selection (e.g., study reservoir‐oriented species such as white bass in main‐channel environments) and habitat‐based classifications to inform species selection (e.g., focus floodplain studies on littoral species such as largemouth bass). Overall, species and habitat identity are important considerations for efficient, effective otolith chemistry studies that inform and advance fisheries and aquatic resource management.