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<br />mainstream Colorado River upstream of the Green River confluence <br />and includes its major tributaries, the Dolores and Gunnison <br />Rivers. The USFWS listed the razorback sucker as an endangered <br />species in 1992. Currently, the razorback sucker population is <br />comprised of mostly older adults. No juveniles have been found <br />in the Upper Colorado Sub-basin since the early 1960s when eight <br />specimens of 90 to 115 mm were collected between Moab and Dead <br />horse Point, Utah (Taba et al. 1965). The lack of successful <br />recruitment is a major limiting factor for razorback sucker <br />populations. <br />Razorback suckers spawn on gravel bars as spring runoff is <br />increasing (Tyus and Karp 1990). Larvae drift downstream (Marsh <br />and Minckley 1989; Minckley et al. 1991) but little is known <br />about the habitats which juveniles occupy. Juveniles have been <br />found in backwaters in the Upper Colorado River Basin (Taba et <br />al. 1965; Gutermuth et al., in press) and adults are known to <br />occupy quiet eddies and pools (Miller et al. 1982). <br />Open water wetlands in flooded bottomlands are believed to be <br />significant nursery habitats for razorback suckers. Potentially, <br />larvae drift into flooded bottomland habitats with the rising <br />water of high spring flows. Based on research of all the <br />endangered Colorado River fish species and a study of flooded <br />bottomlands in the Upper Colorado River Basin (Cooper 1994, <br />included in Appendix A), the characteristics of the Preserve that <br />are likely to be beneficial-to razorback larvae include the <br />following: <br />Warm waters (...°F)??, (how deep??...). <br />Low turbidity, neutral pH. <br />Adequate DO levels through winter (how high??...). <br />Wetlands with high densities of water column Clodocera <br />and Copepoda and a productive benthic community <br />dominated by Chironomids. <br />Vegetation structure for invertebrate production and <br />cover for larvae. <br />Overbank flows of 5 - 20 days in duration which allow <br />razorback sucker larvae and juveniles access to and <br />egress from nursery habitat. <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />Open water within the Preserve of sufficient depth and ' <br />quality to allow overwinter survival of razorback <br />suckers. <br />Permanent water source to maintain wetland habitat <br />between periods of overbank flow. <br />2 <br /> <br /> <br />