Effect of Shallow-Water Habitat Quantity on Young-of-Year Sturgeon Prey Use and Condition Along a Longitudinal Gradient

The lower Missouri River has been highly modified and it is hypothesized that the loss of shallow-water habitat (SWH) has decreased prey availability, negatively affecting young-of-year (YOY) Sturgeon. We sampled for YOY Sturgeon (Scaphirhynchus spp.) in five reaches of the lower Missouri River that varied in amount of SWH (47 to 295 ha) bi-monthly from May through October 2014. For each site, we analyzed prey use and condition in relation to the amount of SWH along a longitudinal gradient of the river. We captured 506 YOY Shovelnose Sturgeon (15 to 120 mm FL) and found diet items were restricted to three macroinvertebrate orders: Diptera, Ephemeroptera, and Trichoptera. Regarding the predominant prey type, number of Diptera larvae eaten peaked at middle reaches and moderate amounts of SWH for fish 41 to 100 mm FL. Both SWH and length affected total lipid percentage with fish ≤ 40 mm FL having the highest lipid content overall. We analyzed diets of three genetically confirmed YOY Pallid Sturgeon (20, 24, 48 mm TL) and each gut contained Diptera larvae. These results provide the first description of YOY sturgeon prey use and condition at a large spatial scale along the lower Missouri River.