Seasonal Movements and Angler Exploitation of an Adfluvial Walleye Population in the Missouri River, Montana

Abstract

An unauthorized introduction of walleye in Canyon Ferry Reservoir (CFR) challenges fisheries managers as the population pioneers new habitat upstream in the Missouri River.  Montana Fish, Wildlife & Parks (MFWP) confirmed walleye in the river upstream of CFR in 2007.  Angler tag returns suggested walleye were abundant in the river.  It was unknown if these were adfluvial walleye originating in CFR, or a discrete fluvial population. Understanding seasonal movements and ecology of walleye in the river will allow managers to effectively monitor and manage these fish.  The objectives of this study were to monitor radio and anchor-tagged walleye movements to quantify movements and determine if two distinct populations exist, establish spatial and temporal densities within the river, and calculate exploitation rates of walleye by anglers in the river.  Overall, most radio-tagged walleye relocated in the river, 88 percent river and 100 percent CFR implanted fish, exhibited seasonal adfluvial movements suggesting, similar to other studies, that two distinct walleye populations are not present. Adfluvial walleye were concentrated in the lower 6.4 km of the river during the annual ascending hydrograph, maintained maximum upstream extent throughout the summer, and out-migrated into CFR by late fall. Radio-tagged walleye only used the river between 17 March and 27 November. We estimated walleye exploitation rates were 21 percent for CFR-tagged walleye and 13 percent for river-tagged walleye.  Exploitation rates for anchor-tagged walleye in this study reflect CFR exploitation rates (18% from 20102014) just prior to this study.  These results suggest that adfluvial Missouri River walleye are seasonally abundant and exploited at similar rates as lacustrine CFR walleye, but no changes to current river walleye management strategies are recommended.  In addition, routine walleye population monitoring surveys and a creel survey are warranted as the adfluvial CFR walleye population continues to adapt, expand, and establish.