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<br />uniform width and swift current. Funk and Robinson (1974) calculated that the <br />length of the Missouri River between Rulo, Nebraska, and its mouth (-SOO river <br />miles) had been reduced by 8 percent and the water surface area had been <br />reduced by 50 percent following channelization. <br /> <br />The Missouri River habitat between and downstream of main stem dams has been <br />altered by removal of snags, reductions in sediment and organic matter <br />transport/deposition, channel degradation, flow modification, hypolimnetic <br />releases, and narrowing of the river through channelization. These activities <br />have adversely impacted the natural river dynamics by reducing the diversity <br />of bottom contours and substrate, slowing accumulation of organic matter, <br />reducing overbank flooding, changing seasonal flow patterns, severing flows to <br />backwater areas, and reducing turbidity and water temperature. <br /> <br />The middle Mississippi River from the mouth of the Missouri River to the mouth <br />of the Ohio River is principally channelized with few remaining secondary <br />channels, sandbars, islands, and. abandoned channels. The middle Mississippi <br />River has been extensively diked to maintain a 2.7 m (9 feet) navigation <br />channel, and flood control levees have reduced the size of the floodplain by <br />39 percent. The surface area of the fluvial landscape in 1968 was 260 km2 <br />(100 mi2) (17 percent islands, 83 percent riverbed), 39 percent less than in <br />1888 (Fremling 1989). The constricted channel and bed degradation have <br />contributed to river fluctuations by as much as 15 m (50 feet) annually, <br />effectively dewatering some secondary channels during low stages (Fremling <br />1989). <br /> <br />Levee construction on the lower Mississippi River from the Ohio River to near <br />the Gulf have eliminated major natural floodways and reduced the land area of <br />the floodplain by more than 90 percent (Fremling 1989). Fremling (1989) also <br />reports that levee construction isolated many floodplain lakes and raised <br />river banks. As a result of levee construction, 15 meander loops were severed <br />between 1933 and 1942. <br /> <br />The pattern of flow velocity, volume, and .timing of the predevelopment <br />Missouri River provided the essential life requirements of native large-river <br />fish like the pallid sturgeon and paddlefish. Hesse and Mestl (1993a) found a <br />significant relationship between the density of paddlefish larvae and two <br />indices (timing and volume) of discharge from Fort Randall Dam. When dam <br />operations caused discharge to fluctuate widely during spring spawning, the <br />density of drifting larvae was lower (R - -0.3728, P - 0.17). Also, when <br />annual runoff volume was highest, paddlefish larval density was highest <br />(R - 0.4014, P - 0.13). Hesse and Mestl (1987) modeled these same two indices <br />of discharge from Fort Randall Dam with an index of year class strength. They <br />demonstrated significant negative relationships between artificial flow <br />fluctuations in the spring and poor year class development for several native <br />fish species, river carpsucker (Carpiodes carpio), shorthead redhorse <br />(Hoxostoma macrolepidotum), channel catfish (Ictalurus punctatus), flathead <br />catfish (Pylodictis olivaris), sauger, common carp (Cyprinus carpio), <br />smallmouth buffalo (Ictiobus bUbalus), and bigmouth buffalo (I. cyprinellus). <br />The sample size of sturgeon was too small to model in that study; however, <br /> <br />""?-,. <br /> <br />11 <br />