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<br />10 <br /> <br />The Colorado River subbasin population shows particular signs of further <br />decline. Catch-per-unit effort rates for larvae, young-of-year, and adult <br />Colorado squawfish are low (Archer et al. 1986). Slow growth and increased <br />early-life mortality in upstream reaches due to much lower temperatures than <br />occur in the lower basin (the demarcation between the Upper and Lower Colorado <br />Basins is Lees Ferry, just downstream of Glen Canyon Dam), compounded with <br />predation by introduced fishes and other man-induced causes, may be important <br />factors affecting recruitment (Kaeding and Osmundson 1988). Osmundson and <br />Kaeding (1990) reported a continued decline in populations of Colorado <br />squawfish in the Colorado River near Grand Junction, Colorado, and cited the <br />nearly SO percent reduction in spring flows as a detrimental factor. <br /> <br />The Green River subbasin currently supports the largest population of Colorado <br />squawfish anywhere in the wild; however, during the past 10 years of intensive <br />study, at least 3 years of reproduction have been lost due to extremes in flow <br />releases from Flaming Gorge Dam and other man-induced problems (Harold Tyus, <br />Personal Communication). In 1983, and again in 1984, extended high releases <br />well into the summer months inundated backwater nursery habitats and flushed <br />larvae downstream. In 1989, extreme drought conditions and extended low-flow <br />releases from Flaming Gorge Dam. coupled with an oil pipeline break and <br />subsequent spill into the Yampa River, may have resulted in a total loss of <br />reproduction in the upper Green River subbasin for that year. Additional <br />projects that would result in significant depletions are planned for the Green <br />River subbasin. <br /> <br />The San Juan River has been developed through several projects, including the <br />Navajo Reservoir, Navajo Indian Irrigation Project, and San Juan-Chama Project. <br />None of these projects have undergone Section 7 consultation under the <br />Endangered Species Act. The current level of development on the San Juan River <br />results in a net depletion of streamflows of approximately 600,000 acre-feet of <br />the mean annual flow. Additional projects are being planned in the San Juan <br />River subbasin that would significantly increase that annual depletion to <br />1,1 million acre-feet (MAF), or approximately SO percent of the mean annual <br />flow of the San Juan River at Bluff, Utah. A once healthy (predevelopment) <br />population of Colorado squawfish has been reduced to a mere few fish that are <br />further threatened by continued development. <br /> <br />BioloGY <br /> <br />The life-history phases that appear to be most critical for the Colorado <br />squawfish include spawning, egg fertilization, and development of larvae <br />through the first year of life. These phases of Colorado squawfish development <br />are tied closely to specific flow events and habitat requirements. <br /> <br />A natural hydrograph with a large spring peak; a gradually declining/descending <br />limb into early summer; and low, stable flows through summer, fall, and winter <br />are thought to create the best habitat conditions for endangered fishes while <br />maintaining the integrity of the channel geomorphology. Tyus and Karp (1989) <br />pointed out the importance of peak flows (spring runoff) associated with <br />