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Last modified
8/11/2009 11:32:57 AM
Creation date
8/10/2009 4:29:28 PM
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UCREFRP
UCREFRP Catalog Number
7996
Author
Wydoski, R. S. and E. D. Wick.
Title
Ecological Value of Flooded Bottomland Habitats to Endangered Fishes in the Upper Colorado River Basin.
USFW Year
1996.
USFW - Doc Type
\
Copyright Material
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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 />
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