9316 - Laserfiche WebLink

Home Browse Search

EXECUTIVE SUMMARY The Green and Colorado River basins include a network of tributaries that contribute to the well-being of endangered Big River fishes. Some tributaries provide habitat used directly by one or more of the fishes, and all tributaries add flow, sediment, and solutes that indirectly affect mainstream habitat. An understanding of the role played by tributaries in direct and indirect ways can aid in developing fish recovery measures. We evaluated the role of major tributary streams for endangered fish recovery using a matrix approach based on quantitative information. However, the need for ranking tributaries for direct and indirect contributions (i.e., assignment of high, medium or low importance) required a more subjective approach. Some streams differed in actual and potential importance because barriers deny fish access to suitable habitat. We have not assigned relative importance to the different types of contributions; to a large extent that may involve policy issues better addressed by the Recovery Program: Tributaries in the Upper Colorado River Basin vary widely in terms of habitat used by the endangered fishes and contributions of flow, sediment, or other constituents affecting habitat in mainstream reaches. We considered the Colorado and Green rivers subbasins separately for assessing contributions, such as flow inputs, and obstacles to recovery, such as nonnative fish. We also considered the Colorado River above its confluence with the Gunnison River, and the Green River above the Yampa River to be tributaries. Highest ranked tributaries of the Colorado River subbasin were the tributary Colorado and Gunnison rivers. Highest ranked tributaries in the Green River subbasin were the Yampa River, tributary Green River, and White River. The Yampa River (including its tributary the Little Snake River) is unique among all of these tributaries because it supports populations and known spawning areas of three of the endangered fishes, and it is considered a recovery area for the fourth. The U.S. Fish and Wildlife Service has designated critical habitat for the Colorado pikeminnow from the Yampa River mouth upstream to Craig, Colorado, and shorter reaches have been designated for the other three endangered fishes. From the standpoint of indirect contributions to the system, the Little Snake River was considered an integral part of the Yampa River basin, because of its role in providing a significant sediment source for the lower Yampa River and mainstream Green River. The movement of Colorado pikeminnow and humpback chub into the lower part of the Little Snake River also indicates an important linkage related to habitat. The Yampa River has escaped much of the water development activity that has greatly altered many other stream reaches, leaving the it mostly unregulated and without significant barriers to endangered fish movement. On an annual basis, the Yampa River contributes about half of the water in the Green River downstream of the confluence of these two rivers. Historically, operation of Flaming Gorge Dam (since 1962) eliminated most or ail of the runoff pulse in the downstream Green River. However, most of the water supplied by the Yampa River occurs during spring runoff, producing the runoff pulse observed in the Green River below the Yampa River confluence. Recovery efforts presently underway will viii