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<br />* * * DRAFT * * * February 11, 1988 <br />BIOLOGICAL CRITERIA FOR USE OF FISH PASSAGE IN THE <br />RECOVERY OF THREATENED AND ENDANGERED FISHES <br />IN THE UPPER COLORADO RIVER BASIN <br />OVERVIEW <br />General <br />Remnant populations of four threatened and endangered endemic fishes are <br />still found in mainstem rivers of the upper Colorado River basin (UCRB)1. <br />These endemic fishes, once abundant in the Colorado River system, however, are <br />threatened with extinction. The steady decline in their range and abundance <br />has concided with the activities of technologic man in the Colorado River <br />basin. However, the exact factors that have caused decline of these fishes <br />has occurred since the early 1900's and that much of the decline is the result <br />of changes to their native habitats brought about by stream alteration. The <br />Colorado squawfish (Ptychocheilus lucius), humpback chub (Gila cypha), and <br />bonytail (Gila elegans) are classified as endangered by the U. S. Fish and <br />Wildlife Service (Service), pursuant to provisions of the Endangered Species <br />Act (Act). It is estimated that the Colorado squawfish exists in only about <br />25% of its original range. The razorback sucker (Xyrauchen texanus) is rare <br />but currently receives no Federal protection. It is, however, listed as <br />endangered by the State of Colorado and protected by the State of Utah, and is <br />a candidate for listing under the Act. <br />The movement of some of these fishes was not well known or understood <br />until the use of radiotelemetry. The majority of movement data collected and <br />available is from adult Colorado squawfish. Of these four fish, the Colorado <br />A <br />!This report applies to the Upper Colorado River above Glen Canyon Dam, <br />excluding the San Juan River.