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<br />d <br />o <br />c-, <br />, ., <br />N <br />-.j <br /> <br />5 <br /> <br />3. determine if range expansion into historic habitat can be accomplished by stocking <br />adult fish; and <br /> <br />4. determine the extent to which existing diversion dams are impeding endangered <br />fish movement. <br /> <br />The Colorado squawfish was listed as endangered on March 11, 1967. Habitat alteration, <br />fragmentation, and degradation arising from dam construction; and competition and predation <br />from introduced non-native fishes have been cited as the major factors responsible for the <br />decline of the species. As a top level predator, the Colorado squawfish may experience <br />bioaccumulation of contaminants from its prey. <br /> <br />The Colorado squawfish evolved as the main predator in the Colorado River and San Juan <br />River systems. The diet of Colorado squawfish longer than 3 or 4 inches consists almost <br />entirely of other fishes (Vanicek and Kramer 1969). The Colorado squawfish is the largest <br />cyprinid (minnow family) native to North America and, during predevelopment times, may <br />have grown as large as 6 feet in length and weighed nearly 100 pounds (Behnke and Benson <br />1983). These large fish are known to be long-lived and may reach 25-50 years of age. The <br />Colorado squawfish now occupies about 1,030 river miles in the Colorado River system <br />(20 percent of its original range) and natural populations are currently found only in the San <br />Juan and other subbasins above Glen Canyon Dam (Tyus and Karp 1990). <br /> <br />Based on early fish collection records, archaeological finds, and other observations, the <br />Colorado squawfish was once found throughout warmwater reaches of the entire Colorado <br />River Basin, including reaches of the upper San Juan River and possibly its major tributaries. <br />Colorado squawfish were apparently never found in colder headwater areas. Seethaler (1978) <br />indicated that the species was abundant in suitable habitats throughout the entire Colorado <br />River Basin prior to the 1850's. Platania and Young (1989) summarized historic fish <br />collections in the San Juan River drainage, which indicated that Colorado squawfish once <br />inhabited reaches above what is now the Navajo Dam and Reservoir near Rosa, New Mexico. <br />Since closure of the dam in 1962 and the accompanying fish eradication program, physical <br />changes (flow and temperature) associated with operation of the Navajo Project have <br />eliminated Colorado squawfish in the upper San Juan River, both from the reservoir basin as <br />well as from several miles of river downstream of the dam. <br /> <br />The life-history phases that appear to be most critical for the Colorado squawfish include <br />spawning, egg fertilization, and development of larvae through the first year of life. These <br />phases of Colorado squawfish development are tied closely to specific habitat requirements. <br />Natural spawning of Colorado squawfish is initiated on the descending limb of the annual <br />hydrograph as water temperatures approach 20. Celsius (C). Spawning, both in the hatchery <br />and in the field, generally occurs in a 2-month timeframe between July 1 and September 1, <br />although high flow water years may suppress river temperatures and extend spawning in the <br />natural system into September. Conversely, during low flow years when the water warms <br />earlier, spawning may occur in late June. <br /> <br />A natural hydrograph with a large spring peak; a gradually declining/descending lim b into early <br />summer; and low, stable flows through summer, fall, and winter are thought to create the <br />