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3 <br />EXECUTIVE SUMMARY <br />Populations of the endangered razorback sucker (Xyrauchen texanus) in the <br />middle Green River have declined since closure of Flaming Gorge Dam in 1962. The <br />apparent cause for the decline is a lack of successful recruitment. Recruitment failure has <br />been attributed to habitat alteration and competition and predation by exotic fishes on <br />early life stages of razorback sucker. This study was conducted to evaluate two of the <br />potential reproductive bottlenecks that might limit recruitment of razorback sucker in the <br />Green River Drainage; (1) reduced larvae production due to sediment deposition on <br />spawning areas, and (2) reduced survival of larvae or juveniles due to lack of timely <br />access to food-rich backwater and floodplain habitats. <br />A paired-site comparison of channel dynamics, hydraulics, temperature, and <br />physical habitat characteristics between known spawning areas in the Green and Yampa <br />Rivers was conducted. Hydrologic data from pre-and post Flaming Gorge time periods <br />was used to assess long-term changes in relevant hydrologic characteristics and changes <br />in the frequency of floodplain inundation. Repeated hydrographic surveys were used to <br />examine patterns in sediment movement and to develop hydraulic models that were used <br />to simulate habitat conditions at both study sites. Channel change was evaluated during <br />water year 2000 and habitat conditions were simulated for runoff during 2000 and 1984. <br />Telemetry was used to evaluate razorback sucker use of the spawning area during the <br />ascending limb of the 2000 runoff cycle in the Green River. Habitat conditions over time <br />for 2000 and 1984 at both study sites were evaluated using maps and duration statistics to <br />represent the period of time during the telemetry study (May 2000) and a period of time