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0 • <br />may naturally or in combination with water diversion structures impede or prohibit return <br />migration of adult fish after spawning. Historically, the Yampa River population of <br />Colorado squawfish has adapted to the occurrence of low -flow conditions during late - <br />summer return migrations, and existing data suggest the population appears stable and <br />has coped with any temporary passage barriers that have occurred. However, lack of <br />data limits understanding of both the proportion of the squawfish population adversely <br />affected by migration barriers, and the potential for enhancement of recovery status of <br />this population through mitigation of existing barriers. In some cases the low flows are <br />thought to create conditions which may be detrimental to population stability of the <br />endangered fish. These potential conditions may become more frequent with added <br />depletions from planned water development activities. <br />The implementation of Task II.A.1 resulted in an assessment of 119 potential fish <br />passage barriers in the Yampa River from river mile 53 to 179 (Hydrosphere 1995). <br />This report concluded the most biologically significant structures with regard to <br />squawfish migration during low flow periods were the Maybell Canal diversion in <br />Juniper Canyon, and the Patrick Sweeney /K Diamond diversion near Government Bridge. <br />The report also emphasized that an unresolved issue was whether Cross Mountain <br />Canyon, downstream of the diversion structures identified was also a potential natural <br />obstruction to squawfish passage, and if so, would render improvements to the upstream <br />structures ineffective. <br />Discussions within the U.S. Fish and Wildlife Service and Biology Committee for the <br />Recovery Program and assessment of the results provided in a draft report on flow <br />recommendations for endangered fish in the Yampa River (Modde and Smith 1995) <br />resulted in the determination that insufficient data were available to document whether <br />Cross Mountain Canyon or the other two man -made structures represented a passage <br />barrier to adult Colorado squawfish under low -flow conditions. Further, a task group <br />was assigned to develop a scope of work describing hydraulic and biological studies to <br />further assess the potential passage issue. <br />This scone of work focuses on the potential problem of passage for adult Colorado <br />squawfish during their return upstream migration to home ranges in the Yampa following <br />spawning In order to evaluate the potential need for improvement of passage at <br />diversion structures in the Yampa River for the benefit of Colorado squawfish, an <br />understanding of the limiting reaches over which the Colorado squawfish will be <br />migrating must be developed. This understanding may be developed by selecting and <br />studying representative limiting reaches of the Yampa River between Craig and the <br />confluence with the Green River. <br />IV. Study Goals, Objectives, End Product: <br />Study Goal: determine if natural barriers and man-made diversion structures in the Yampa <br />River adversely affect upstream passage of migrating adult Colorado squawfish. <br />ON <br />