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Hypothesis 9: Higher spring flows from the Aspinall Unit will improve the <br />ability of the Gunnison and Colorado rivers to clean spawning substrate, <br />to maintain sand and silt substrates in nursery areas, and to maintain <br />natural channel characteristics. <br />Thompson (1984) showed that the Aspinall Unit reduced the sediment load <br />of the Colorado River. However, the effect of reduced sediment levels on <br />riverine habitat is unknown. We5Xdonot know what duration and level of flow <br />is necessary to clean the cobble and rubble areas believed important for <br />spawning. The ability of the Gunnison and Colorado rivers to move substrates <br />of various sizes should be investigated. Also, level and duration of flows <br />necessary to maintain natural channel chacteristics should be investigated. <br />Flow changes have reduced the rivers' ability to maintain channel width, but <br />this change has been compounded by construction of dikes in populated areas <br />and encroachment of tamerisk on streambanks and islands in non-populated <br />areas. The relative contribution of these factors (as well as others that may <br />be important) should be evaluated and management suggestions developed. <br />Hypothesis 10: Reproductive success of humpback chub in Black Rocks and <br />Westwater Canyon will be enhanc"ed by high spring flows from the Gunnison <br />River. Survival of young chubs will improve under a more natural flow <br />regime. <br />Although relationships are unknown at present, it is very likely that <br />reproductive success of humpback chubs is related to spring runoff, or at <br />least to conditions created by spring runoff. The reproductive success of <br />humpback chubs should be monitored. This will require more studies than <br />currently done under ISMP (although these additional studies should be closely <br />40 <br />