Effects of Reservoir Elevation and Spatial Synchrony on Walleye Recruitment in Lake Oahe, Missouri River

Abstract

AbstractRecruitment is an important driver of fish population abundance and size structure and can be affected by a variety of density‐dependent and density‐independent factors. Walleye Sander vitreus populations often exhibit variable year‐class strength, which has been attributed to a suite of factors. In this study, we quantified variability in Walleye recruitment, assessed within‐lake recruitment synchrony, and modeled recruitment variability for year‐classes that were produced from 1988 to 2013 in Lake Oahe, a large Missouri River reservoir. The objectives of this study were to determine (1) whether Walleye recruit annually, (2) whether Walleye recruitment is spatially synchronous, and (3) whether Walleye recruitment is better described by biotic or abiotic factors. The variability of Walleye recruitment was indexed by using gill‐net catch of age‐2 Walleye across nine locations in Lake Oahe, and factors affecting recruitment were evaluated by using stock–recruit analysis. Over the 26 years that were assessed, all year‐classes were present and four exceptionally large year‐classes were produced. Recruitment synchrony was apparent among locations within Lake Oahe, but this relationship was largely influenced by the spatial synchrony of the four exceptionally large year‐classes and was no longer detectable when those year‐classes were removed. The relative abundance of age‐4 and older Walleye, taken as an index of spawner abundance, was a poor predictor of Walleye recruitment, indicating that Walleye recruitment was regulated by density‐independent factors across the range of observations. The interactive effects of reservoir elevation and elevation change improved model fit to explain 59% of the recruitment variation and indicated that increased elevation from the previous year improved recruitment. Our results indicate that Walleye recruitment may be favored by increasing the water levels in the reservoir in spring.