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<br />. <br /> <br />~? <br /> <br />construction of mainstem dams (Osmundson and Kaeding 1991). The <br />construction of dikes coupled with the reduction of high spring flows <br />has altered the natural hydrograph and either reduced or eliminated <br />regular flooding of bottomlands. It is believed that flooded <br />bottomlands may have served as nursery areas for the razorback sucker, <br />Xyrauchen texanus (McAda 1977; Osmundson and Kaeding 1991). In <br />addition, Osmundson and Kaeding suggested that oxbow lakes and flooded <br />pastures in the Grand Valley near Grand Junction; Colorado. were <br />historically the primary spawning habitats of the razorback 'sucker. <br />They also suggested that low velocity, off-channel habitats were used <br />by adult Colorado squawfish (Ptychochei7us 7ucius) during high <br />streamflows. <br /> <br />Numerous studies (Grawboski and Hiebert 1989; Tyus and Karp 1989: <br />Wydoski and Wick 1994) have suggested the importance of seasonal <br />flooding to river productivity. Other studies have suggested that <br />flooded bottomlands were important to adult razorback sucker for <br />feeding prior to and after spawning and also important for rearing of <br />their young (Tyus and Karp 1989). Adult fish may have used these off- <br />channel habitats for "velocity shelters' to escape the high water <br />velocities from the spring runoff. <br /> <br />The turbid rivers in the upper basin are not very productive for <br />zooplankton that are essential for survival during the early life <br />stages of the razorback sucker. When compared to the riverine <br />environment and river backwaters. inundated bottomlands produce the <br />highest densities of zooplankton (Grabowski and Hiebert 19B9; Mabey and <br />Shiozawa 1993). Although predation has been documented to be a <br />limiting factor in survival of larval razorback sucker in the lower <br />basin (Minckley et al. 1991). starvation may also limit survival (Marsh <br />and Langhorst 1988: Papoulias and Minckley 1990). It is hypothesized <br />that the loss of these productive flooded bottomland habitats appears <br />to be limiting the recruitment of the razorback sucker in the upper <br />Colorado River basin because of the lack of the right sizes of food <br />organisms at the right time and in sufficient quantity (Wydoski and <br />Wick 1994). <br /> <br />Flooded bottomland habitats occur in broad valleys along low gradient <br />stream reaches. Bottomlands are off- or out-of-channel habitats that <br />include oxbow lakes, former side channels in broad valley floodplains. <br />ponds, and wetland depressions. During high flow events. some of these <br />off-channel features were temporarily connected to the river. Former <br />natural riverine features could be integrated back into the historic <br />floodplain by removing portions of man-made dikes or natural <br />obstructions (e.g., gravel/sand bars). <br /> <br />~ <br />