Spatial Drift Dynamics of Shovelnose Sturgeon and Pallid Sturgeon Prelarvae in the Transition Zone of Ft. Peck Reservoir

Abstract

Habitats in reservoir headwaters may cause high mortality of sturgeon prelarvae. Short inter-reservoir reaches export drifting prelarvae from hatch locations into reservoirs. However, flooded vegetation could entrain prelarvae. We used 2 day post hatch (dph) shovelnose sturgeon (Scaphirhynchus platorynchus) and 1-dph pallid sturgeon (Scaphirhynchus albus) to determine the spatial dynamics of drifting prelarvae.We released 220,000 2-dph shovelnose sturgeon 4 km upstream of Ft. Peck Reservoir and 135,000 1-dph pallid sturgeon 2.5 km upstream of the reservoir the following day. We recaptured shovelnose sturgeon prelarvae with nets deployed along three transects of the transition zone and within the headwaters of the reservoir.We sampled 5148.2 m3 of water and recaptured 323 prelarval shovelnose sturgeon for a recapture rate of 0.14 percent. Fifty-nine percent of recaptured prelarvae were recaptured from the thalweg, 12 percent from the flooded vegetation-main channel interface, 9 percent from the channel border, and 19 percent from the zero-velocity area of Ft. Peck Reservoir. We recaptured pallid sturgeon prelarvae with nets deployed along one transect of the transition zone and within the headwaters of the reservoir. We sampled 6608.5 m3 of water and recaptured 397 pallid sturgeon prelarvae for a recapture rate of 0.29 percent. Twenty one percent of prelarvae were recaptured within the thalweg, 0.25 percent were recaptured along the channel margins, and 79 percent from the zero-velocity area of Ft. Peck Reservoir. Although recapture rates were low, the majority of prelarvae were captured in the thalweg and transported to the headwaters of Ft. Peck Reservoir. The drift dynamics observed in this study provide a springboard for further research.