Why did the Walleye Cross the Reservoir? Explaining Adult Walleye Use of the Missouri River Upstream of Canyon Ferry Reservoir to Toston Dam

• Main Author: Traxler, Tanner M
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2017
• Subjects: walleye yellow perch missouri river toston; Aquaculture and Fisheries; Catostomus catostomus
• Online Access: https://scholarworks.umt.edu/utpp/147; https://scholarworks.umt.edu/context/utpp/article/1157/viewcontent/auto_convert.pdf

Over the last decade, walleye (Sander vitreus) have been increasingly using the Missouri River upstream of Canyon Ferry Reservoir to Toston Dam, and Montana Fish, Wildlife, and Parks wants to understand why these walleye are moving upstream and how it could impact the existing fish community in the river. To understand if this expansion of habitat could be associated with spawning and/or foraging, we examined the composition and distribution of juvenile fish in the area. Specifically, the presence of juvenile walleye would indicate that adult walleye were using the river to spawn and/or if there were abundant prey fish available then adults might be increasingly using the river to feed. To ensure a representative data set, we divided the 23-mile-long stretch of river into three sampling sections. In each section, juvenile fish were sampled using beach seines and mini-fyke nets across pool, riffle, run, and backwater habitats. Each section was sampled twice during the summer of 2016, once in late July or early August and again in mid-August. We captured 26,510 fish, with yellow perch (Perca flavescens), white sucker (Catostomus catostomus) and longnose dace (Rhinichthys cataractae) being the most common species captured. Only 16 of these fish were juvenile walleye, all coming from sampling locations at the interface of the river floodplain and the reservoir; no juvenile walleye were found in the river upstream of this interface. Based on these results, it appears that walleye did not use the river to spawn. However high densities of yellow perch, one of the walleye’s favorite prey items, suggests that adult walleye are using this stretch of river to feed. Additionally, classification and regression tree results of habitat associations indicate that perch occurred in habitat with characteristics preferred by walleye, suggesting that walleye may impact the perch population the most in the future.