Effect of Shallow-water Habitat Quantity on Young-of-year Shovelnose 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. Young-of-year sturgeon (Scaphirhynchus spp.) from five reaches of the lower Missouri River that varied in amount of SWH (47 to 295 ha) were sampled bi-monthly from May through October in 2014 and 2015. For each site, I analyzed prey use and condition in relation to the amount of SWH along a longitudinal gradient of the river. I analyzed 506 YOY shovelnose sturgeon in 2014 and 569 in 2015 (14 to 120 mm FL) and found diet items were restricted to three macroinvertebrate orders: diptera, ephemeroptera, and trichoptera. In 2015, YOY shovelnose sturgeon consumed nearly twice as many prey as in 2014 and had many fewer instances of empty stomachs. Regarding the predominant prey type, number of diptera larvae eaten peaked at middle reaches and moderate amounts of SWH in 2014 and high numbers were consumed at sites further downstream and as SWH increased in 2015. The number of diptera larvae consumed grew exponentially with length, however, in 2015, rate of diptera larvae consumed was least in high amounts of SWH. Prey quantity did not appear to be limited and factors beyond amounts of SWH appear to be affecting prey use and survivorship of YOY shovelnose sturgeon. The highest percent lipid (i.e. body condition) for YOY shovelnose sturgeon was at lengths ?40mm, attributed to assimilation of the yolk sac. Condition was best explained by location along the river continuum, increasing with increased distance upstream (r2 ? 0.27). An interannual influence was observed with average percent lipid in lengths 41-120mm being lower in 2014 than in 2015. Emaciated and healthy control YOY shovelnose sturgeon were acquired to compare to the condition of wild-caught fish. In 2014, length categories >41mm were not statistically different from emaciated specimens and, in 2015, only length category 101-120mm differed from control specimens (P ? 0.05). These results provide the first description of YOY sturgeon prey use and condition at a large spatial scale along the lower Missouri River.Natural Resources and Ecology Managemen

The influence of depth and velocity on age‐0 Scaphirhynchus sturgeon prey consumption: Implications for aquatic habitat restoration

After the pallid sturgeon (Scaphirhynchus albus) was listed as endangered in 1990, a variety of management actions focusing on early life history needs have been implemented to aid species recovery. Given the scarcity of age‐0 pallid sturgeon, managers and scientists have relied on sympatric congeners to evaluate the effectiveness of management actions in the short term; however, increased understanding of habitat requirements for age‐0 Scaphirhynchus sturgeon is still needed to appropriately focus management efforts. Recently, a lack of food‐producing and foraging habitats were proposed as potential limiting factors for pallid sturgeon, and the purpose of this study was to evaluate the current definition of these habitats at multiple spatial scales using data from age‐0 Scaphirhynchus sturgeon (shovelnose sturgeon [Scaphirhynchus platyrhynchus] or hybrid [shovelnose sturgeon x pallid sturgeon]). Results showed the water depths and velocities that currently define age‐0 pallid sturgeon foraging habitat had little effect on age‐0 Scaphirhynchus sturgeon prey consumption. Similar results occurred when evaluating the relationship between prey consumption and food‐producing habitat present 10, 20, and 30 days before capture. Assuming that individuals captured during this study were a valid surrogate, these results suggest that increasing foraging and food‐producing habitat as defined by the current depth and velocity criteria is unlikely to result in the desired benefits of increased growth and survival of age‐0 pallid sturgeon