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<br />floodplain was only inundated 6 times during the 47-year period for over 20 days. <br />More recently, FLO Engineering, Inc. (1995) estimated that a streamflow of 20,300 <br />cfs was required for extensive inundation of the middle Green River floodplain <br />on the Ouray National Wildlife Refuge. <br /> <br />Other examples of ephemeral flooding include the Escalante State Wildlife Area <br />on the Gunnison River, downstream of Delta, Colorado (Cooper and Severn 1994c) <br />and Moab Slough on the Colorado River, immediately upstream from Moab, Utah <br />(Cooper and Severn 1994a). Cooper and Severn estimated that a streamflow of <br />12,000 to 15,000 cfs was required for overbank flooding at that site. A <br />streamflow of 15,000 cfs occurred 31 times during a 97-year period of record <br />(1896-1993). The duration of flooding at this streamflow occurred only 8 times <br />for over 25 days. Pre-dam (1897-1965) streamflows that were greater than 10,000 <br />cfs on the Gunnison River were about 3 weeks in duration but the post-dam (1966- <br />1993) streamflows were less than 1 week at flows greater than 10,000 cfs. Cooper <br />and Severn (1994a) estimated that streamflows of 40,000 cfs were required for <br />overbank flooding at Moab Slough. This flow occurred 26 times during the 70-year <br />period of record (1924-1993) but only 6 times between 1963 and 1993. The <br />duration of inundation at Moab Slough over 25 days only occurred 5 times. <br /> <br />Even fl oodp 1 a in habitats that become inundated for a short time can produce <br />relatively high densities of zooplankton as in the flooded willow habitat of Moab <br />Slough along the Colorado River (Table 2; Cooper and Severn 1994b). A short <br />duration of inundation in bottomland habitats was apparently sufficient to <br />maintain self-sustaining populations for the small number of native species that <br />constituted the historic fish community in the Upper Colorado River Basin. <br />However, a short duration of bottomland habitats is probably not sufficient for <br />survi va 1 of 1 arva 1 nat i ve fi shes today since 76.4% of the fi sh commun i ty is <br />composed of nonnative fishes (Tyus et al. 1982). As indicated earlier, predation <br />and competition on larval razorback suckers by the nonnative fishes is probably <br />the primary factor that drastically reduces or prevents recruitment of this <br />species today. <br /> <br />It is imperative to integrate the control of nonnative fishes and <br />augmentation/restoration stocking of captive-reared razorback suckers with <br />habitat enhancement/restoration efforts. Enhancement or restoration of <br />biological, chemical, and physical conditions that are perceived to be important <br />in nursery sites for razorback sucker can be accomplished by: (1) removal of <br />levees to allow periodic flooding of lowlands, (2) providing a longer duration <br />of i nundat ion in fl oodp 1 a ins, embayments, and backwaters by reopera t i on of <br />releases from reservoirs, and (3) reconnection of the main channel with off- <br />channel oxbow lakes and ponds. The removal of levees coupled with higher spring <br />releases that mimic the historic hydrographs from upstream dams provide the best <br />way to reconnect mainstem and tributary rivers with productive floodplain areas. <br />Because of other demands on the use of Colorado River water, extensive flooding <br />of bottomland habitats will not be possible. Reconnection of lower floodplain <br />terraces with the river will increase the production of zooplankton required by <br />the early life stages of the endangered fishes. However, we agree with Stanford <br />(1994) who believes that negative interactions (i.e., predation and competition) <br />by nonnat i ve fi shes may 1 i mi t the recovery of the endangered Colorado River <br />fishes regardless of possible streamflow provisions. <br /> <br />14 <br />