Otolith Microchemistry Advances Walleye Research and Management in Missouri River Reservoirs

In response to historic flooding, we used otolith microchemistry to investigate environmental history of walleye Sander vitreus in four Missouri River reservoirs (Lakes Oahe, Sharpe, Francis Case, and Lewis and Clark). Spatial variability in water Sr:Ca and Ba:Ca concentrations, particularly among tributaries, was reflected in the chemical otolith signatures of age-0 and adult walleye, permitting retrospective examination of natal origins, movement, and entrainment. Linear discriminant function reclassification accuracies to natal sites were high (≥ 79%) for age-0 and adult walleyes. The Moreau River and Cannonball River were particularly important for reproduction in Lake Oahe, as were the Lewis & Clark Delta and select embayments and mainstem sites in southern reservoirs. Walleye movement within and among impoundments was dominated by downstream passage and site residency (rather than upstream movement) before, during, and after the flood. The percentage of entrained walleye progressively increased moving downstream from Lake Sharpe (18.87%) to Lake Francis Case (24.39%) to Lewis & Clark Lake (34.15%). Nearly two-thirds (64.71%) of entrained walleye moved through dams during the disturbance. Otolith microchemistry is an effective environmental history tool in Missouri River reservoirs. It indicates inter-reservoir connectivity of walleye populations and illustrates the importance of collaborative riverscape management across state boundaries.