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BIOLOGICAL MERITS OF FISH PASSAGE AS PART OF <br />RECOVERY OF COLORADO SQUAWFISH IN THE <br />UPPER COLORADO RIVER BASIN <br />INTRODUCTION <br />i <br />Wild populations of Colorado squawfish Ptychocheilus lucius, a large, piscivorous <br />cyprinid endemic to the Colorado River basin, inhabit the major rivers of the upper <br />basin'. Though formerly abundant in the Colorado River system, the Colorado <br />squawfish is now threatened with extinction and is classified as an endangered <br />species by the U.S. Fish and Wildlife Service (Service), pursuant to provisions of the <br />Endangered Species Act. The declines in Colorado squawfish range and abundance <br />have been coincident with the activities of technologic man in the basin. Although the <br />factors that have caused this decline are not precisely known, it is believed that <br />physical changes to natural habitats resulting from stream alteration and the <br />modification of discharge regimes downstream from dams, the introduction of non- <br />native fishes, and altered water quality (including temperature) are largely responsible. <br />Blockage of Colorado squawfish movement by dams and water-diversion <br />structures has also been suggested as an important cause of the decline of this <br />species in the upper Colorado River basin (Tyus 1984). The movement patterns of <br />Colorado squawfish did not become apparent until recent years, when studies using <br />radiotelemetry techniques showed that adult Colorado squawfish sometimes exhibit <br />long-distance movements. Most movement occurs near the spawning period and is <br />------------------------------------------------------------------------------------------------------------------------- <br />'This report addresses the upper Colorado River basin above Glen Canyon Dam, <br />excluding the San Juan River.