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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

Brian D.S. Graeb


River regulation has altered the structure and dynamics of many riverine ecosystems, most notably through construction of large dams. Much is known about downstream consequences of river regulation. Recently, studies have examined the upstream influence of river regulation because conservation and management of regulated rivers requires a riverscape approach (e.g. linking reservoirs, mainstem rivers, and tributaries) to develop adaptive management plans. The Missouri River in North Dakota was impounded in 1956, creating a highly regulated intra-reservoir section with mainstem riverine and reservoir habitat. This reach of the Missouri River, known as the Garrison Reach, has several tributaries that may provide important riverine functions to the mainstem (e.g. seasonal increases in discharge, sediment, and biota). Tributaries often support fish assemblages unique from the mainstem and also serve as alternate habitats for mainstem fish species during various life history stages (i.e. spawning and rearing). To better understand the role of tributary streams within the Garrison Reach Riverscape, I examined the effects of mainstem river regulation on tributary fish assemblages, and assessed the reproductive contributions of tributary streams to the regulated river environment. To examine the effects of mainstem river regulation on tributary fish assemblages, I estimated spatial and temporal changes in fish assemblages from a constructed database of historic and recent fish survey data. I calculated family and species richness, developed a status classification system, and calculated a similarity index to estimate change in fish assemblages. Total species richness increased, whereas native species remained constant. Of the species considered missing (5), rare (2), and declining (17), the majority (19) had limited historic distributions, whereas many fishes with widespread distributions were stable or expanding. Moreover, many of the species classified stable or expanding were habitat generalists. Fish assemblages in tributaries increased in similarity at a rate of 3.3%, suggesting that taxonomic homogenization is occurring although at a slower rate than the rest of the U.S. (7%). Mainstem river regulation in the Garrison Reach has enriched tributaries near the dam and in the reservoir environment, while tributaries not directly adjacent to these habitats (i.e. middle reach) experienced species losses, presumably from river regulation (e.g. loss of dispersal corridors and altered flow regime). Larger tributaries not only displayed less species turnover between time periods, but are experiencing taxonomic homogenization, while smaller tributaries exhibited higher species turnover and appear to be differentiating. To assess the reproductive contributions of tributary streams to the regulated river environment, I quantified the abundance of larval fishes in five tributaries within the Garrison Reach. Larvae from three families (Catostomidae, Cyprinidae and Percidae) were collected during the spring and summer of 2009 and 2010. Larvae of other fishes known to occur in the Missouri River (e.g. Esocids, Ictalurids and Moronids) were not captured during larval sampling. This suggested that tributaries provide important spawning areas for many Missouri River fish species (e.g. walleye), while other species likely spawn elsewhere (e.g. main channel). High spring discharge appeared to increase reproductive success of Catostomidae and walleye, potentially because of a large increase in the availability of reproductive habitat. Variation in abundance between years indicated that larger tributaries may be more consistent areas of reproduction. Catches of fish larvae were much higher in smaller tributaries during the flood year (2009) and minimal during a normal discharge year (2010). This indicates smaller tributaries such as Beaver Creek may have large reproductive contributions to the Garrison Reach during flood years, but reproductive contributions may be limited during normal or low water years. My results suggest that tributaries provide important spawning areas for many Missouri River fishes, and likely contribute to the persistence of fish species within the regulated river environment of the Garrison Reach.

Library of Congress Subject Headings

Fishes -- Missouri River
Fishes -- North Dakota
Missouri River -- Regulation


Includes bibliographical references (page 49-57)



Number of Pages



South Dakota State University


Copyright © 2010 McLain S. Johnson. All rights reserved.