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" 0024~n MANAGEMENT PLAN INTRODUCTION Purpose and Need The Colorado River Basin encompasses 245,000 square miles in the southwestern United States. Roughly the same size as the Columbia River Basin, its annual average yield is less than 7% that of the Columbia. Moreover, demand for water in this arid region in many years is greater than the volume of water available. In November 1922, the Colorado River Compact was signed, allocating 15 million acre-feet (MAF) of the Colorado River equally between the Upper Basin states (Colorado, New Mexico, Utah and Wyoming) and Lower Basin states (Arizona, California and Nevada). Under the Compact the Upper Basin must deliver an annual average of7.5 MAF to the Lower Basin during any I O-year period (Geit 1997). Lake Powell, a 27-MAF reservoir behind Glen Canyon Dam, allows Upper Basin states to store water during periods of surplus to meet their Compact obligations to the Lower Basin during periods of drought. Glen Canyon Dam effectively serves as the boundary between Upper and Lower basins. Danuned and di verted for irrigation, municipal and industrial consumption, the Colorado River and many of its major tributaries have become a series of lakes and cold, clear tailwaters. Large dams attenuate peak flows, increase base flows and significantly reduce or modify the habitats to the detriment of many endemic fish species adapted to wann, turbid, free-flowing rivers, Native species evolved under a highly variable hydrologic regime, characterized by seasonally high flows in spring and dramatically lower flows in late summer and fall. Reservoirs and their tailwaters also create conditions conducive to propagation of highly valued nonnative game fishes, several species of which were stocked or escaped to the river in the past. These and other nonnative fishes inadvertently introduced to the basin compete with and/or prey upon many native fish species. The Endangered Species Act (ESA) was enacted in 1973 to identify and conserve threatened and endangered species, It requires the U.S. Fish and Wildlife Service (Service) to consider the status of, and potential threats to, plant and animal species in determining whether it is appropriate to list these species as threatened and endangered, Section 4(a)(I) ofthe ESA identifies five threat factors: (I) present or threatened destruction, modification, or curtailment of its habitat or range; (2) overutilization for commercial, recreational, scientific or educational purposes; (3) disease or predation; (4) inadequacy of existing regulatory mechanisms; or (5) other natural or manmade factors affecting its continued existence. If one or more of these factors is met for any species, that species should be listed as endangered or threatened. Pursuant to this section, the Service listed as endangered two fish species endemic to the Colorado River Basin: bonytail (Gila elegans) and razorback sucker (Xyrauchen texanus), Two other endemic Colorado River species, the humpback chub (Gila cypha) and Colorado squawfish (Ptychocheilus lucius), now referred to as the Colorado pikeminnow, originally were listed on March II, 1967 (32 FR 4001) and were among the first species listed under the ESA on June 4, 1973 (38 FR No. 106). Populations of these fishes have declined throughout their historic range due largely to habitat loss or degradation. Nonnative fish represent a significant impediment to recovery. Section 4(c)(2) requires that the status oflisted species be reviewed at least once every 5 years to determine if species should be "delisted" (i,e., removed from the list), "down listed" from endangered to threatened status, or reclassified from threatened to endangered status. Section 4(1)( I) requires the Service to develop and implement "recovery plans" that incorporate "a description of ~ r:i Management Plan for Endangered Fishes in the Yampa River Basin I