The five reservoirs within Nebraska's Republican River watershed (Swanson Reservoir, Enders Reservoir, Red Willow Reservoir [also referred to as Hugh Butler Lake], Medicine Creek Reservoir [also referred to as Harry Strunk Lake], and Harlan County Lake) were built primarily for flood control and irrigation, resulting in large in-reservoir water-level fluctuations within and among years. These reservoirs also provide important fisheries for anglers in southwest Nebraska, with walleye and white bass being of particular importance. Continued annual stockings of walleye have been necessary to maintain populations because natural production is limited. In contrast, white bass populations are self-sustaining, although recruitment is erratic (i.e., weak or missing year-classes are common) in all but Harlan County Reservoir.
GoalsThe purpose of this project was to gain an understanding of the factors affecting recruitment of walleye and white bass in irrigation reservoirs. The primary foci were to document the relative importance of spawning habitats, and the timing of recruitment bottlenecks for walleye and white bass in southwest Nebraska irrigation reservoirs. A secondary focus was development of a general walleye population model that incorporated uncertainty in frequency of missing year classes.
We are assessing temporal and spatial trends in abundance of larval walleye and white bass from 2008 to 2011, and comparing with to trends in abundance of zooplankton- the primary prey of the larval fishes- to understand annual variability in fish production within these systems. We are also building a mathematical model to understand population responses to missing year classes. Information gained from this project will further our understanding of the ecology of reservoirs in semi-arid regions.