Fish-Habitat Associations in Small Backwaters of the Upper Missouri River, North Dakota

I evaluated habitat characteristics and fish assemblages associated with small backwaters of the Upper Missouri River, North Dakota. Backwaters sampled ranged in size from 0.002 to 0.44 ha with a mean area of 0.08 ha and were located relatively close to the main channel of the Missouri River (mean = 48 m from river\u27s edge). Maximum depths ranged from 0.15 m to 1.05 m. One third of backwaters sampled contained woody debris greater than 0.1 m in diameter, and 71 % contained macrophytes. Amounts of large woody debris and water temperature differed significantly among backwaters located in the tailrace, middle and lower river segments of the Garrison Reach. Woody debris and water temperatures in backwater sites were positively correlated with distance from Garrison Dam. I collected a total of 20 species of fishes from backwater sites of which 17 were native to North Dakota. White suckers (Catostomus commersoni) and fathead minnows (Pimephales promelas) were the most abundant (45.2% and 26.5% of total catch respectively) and frequently occurring fishes collected (56.3% of backwaters sampled). Common carp ( (\prinus carpio ), shortnose gar (Lepisosteus platostomus ). white bass (Marone chrysops), golden shiners (Notemigonus crysoleucas), and largemouth bass (Microptems salmoides) occurred infrequently (\u3c7%) in backwater areas, and were found in low relative abundance. Based on canonical correspondence analysis, I identified two distinct fish assemblages that utilize small floodplain backwaters; one group was comprised of cyprinids and catostomids, while the other consisted of centrarchids and percids. The two assemblages generally preferred different habitat characteristics and were rarely found in large numbers together. The cyprinid-catostomid assemblage tended to be associated with cooler water and wider and shallower backwaters, whereas the centrarchid-percid assemblage preferred backwaters with increased habitat complexity (i.e., greater depth, more macrophytes and large woody debris) and warmer water. Although impoundments have dramatically altered the natural hydrograph and floodplain characteristics of the Missouri River, backwater habitats can provide important spawning and rearing areas for a diverse array of fishes. Fish-habitat associations identified in this study should prove useful for enhancing management efforts aimed at conservation of riverine fishes