Date of this Version
American Fisheries Society Symposium 45:249–291, 2005.
The longest river in North America, the Missouri, trends southeast from Montana across the mid continent of the United States, 3,768 km to its confluence with the Mississippi River near St. Louis, Missouri. Frequent flooding, a shifting, braided channel, and high turbidity characterized the precontrol “Big Muddy.” Major alterations occurred over the past century primarily for flood protection, navigation, irrigation, and power production. Today, the middle one-third of its length is impounded into the largest volume reservoir complex in the United States and the lower one-third is channelized, leveed, and its banks stabilized.
Spatial and temporal patterns of Missouri River fishes are reviewed for the main channel, floodplain, and major reservoirs. Twenty-five families, containing 136 species, compose its ichthyofauna. Seven families represent 76% of total species richness, with Cyprinidae (47 species), Catostomidae (13), Centrarchidae (12), and Salmonidae (10), the five most specious. Native fishes compose 79% of the river’s ichthyofauna with representatives of four archaic families extant: Acipenseridae, Polyodontidae, Lepisosteidae, and Hiodontidae. Fifty-four percent of Missouri River fishes are classified as “big river” species, residing primarily in the main channel, and 93% of these are fluvial dependent or fluvial specialists. Significant floodplain use occurs for 60 species. Many of its big river fishes are well adapted for life in turbid, swift waters with unstable sand-silt bottoms.
Populations of 17 species are increasing and 53% of these are introduced, primarily salmonids, forage fishes, and Asian carps. Ninety-six percent of the 24 species whose populations are decreasing are native. Fishes listed as globally critically imperiled and federally endangered (G1) or globally vulnerable (G3) include pallid sturgeon Scaphirhynchus albus (G1), lake sturgeon Acipenser fulvescens, Alabama shad Alosa alabamae, sturgeon chub Macrhybopsis gelida, and sicklefin chub M. meeki (G3). Eleven fishes are listed by two of more of the seven main-stem states as imperiled; all are big river species.
Richness increases going downriver from 64 species in Montana to 110 species in Missouri with 36% of widely distributed taxa absent below one or more reservoir. Longterm fish collections from several states show declines in sauger Sander canadensis throughout the river and decreases in the lower river of several big river fishes (e.g., sturgeons, chubs, Hybognathus spp.). Spatiotemporal changes in Missouri River fishes reflect interactions between natural (climate, physiography, hydrology, and zoogeography) and anthropogenic (impoundment, geomorphic, flow, and temperature alterations, and introduced species) factors. Recurrent droughts and floods and persistent stakeholder conflicts over beneficial uses have recently directed national attention to Missouri River issues. Acquisition of floodplain lands and channel and floodplain rehabilitation programs are underway to improve habitat in the lower river. Unfortunately, many are site specific and few have included explicit ecological objectives and performance evaluations. Several proposals for flow normalization are being considered, but remain controversial.