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<br />C") <br /><":) <br />C:.;l <br /> <br />In August 1997, 100,000 young-of-year Colorado squawfish will be obtained from Dexter <br />National Fish Hatchery and Technology Center. A unique TC stain and/or chemical spray <br />mark will be used to batch mark five groups of 20,000 fish within the first week after <br />swim-up, These marks will allow the identification of fish from individual stocking events. <br />The fish will be stocked at an average of 20-40 mm total length approximately 1 kilometer <br />(km) above each of five reaches of the San Juan River (parenthetical references are the <br />geomorphic reaches encompassing the locations): Hogback (#5 - Mixer to Hogback), <br />Mixer (#4 - Aneth to Mixer), Montezuma Creek (#3 - Chinle to Aneth), John's Canyon (#2 <br />-Canyon), and Grand Gulch (#1- Lake powell influence). <br /> <br />~ <, <br /> <br />.;:.. <br />o <br /> <br />All low-velocity habitats throughout the five geomorphic reaches will be sampled one week <br />following the release of Age-O Colorado squawfish. This initial sampling will determine if <br />low-velocity habitats within each reach are retaining fish or if fish are selecting these <br />habitats. After the first sampling, each reach will be sampled bi-weekly until deemed <br />unnecessary. The later sampling will determine the duration that fish are retained within <br />low-velocity habitats in each reach. This intensive sampling schedule will allow the <br />monitoring of dispersal, habitat selection. and movement of fish among habitats and <br />reaches over time. <br /> <br />BASIS FOR BIOLOGICAL OPINION <br /> <br />COLORADO SOUAWFISH <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 <br />Benson 1983). These large fish are known to be long-lived and may reach 25-50 years of <br />age. The Colorado squawfish currently occupies about 1,030 river miles in the Colorado <br />River system (20 percent of its original range) and natural populations are currently found <br />only in the San Juan and other subbasins above G'en 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 <br />tributaries, Colorado squawfish were apparently never found in colder he~adwater areas. <br />Seethaler (1978) indicated thl'lt the species was abundant in suitable habitats throughout <br />the entire Colorado River Basin prior to the 1850's. Platania and Young (1989) <br />summarized historic fish collections in the San Juan River drainage, which indicated that <br />Colorado squawtish once inhabited reaches above what is now the Navajo Dam and <br />Reservoir near Rosa, New Mexico. Since closure of the dam in 1962 and the <br />accompanying fish eradication program. physical changes (flow and temperature) <br />associated with operation of the Navajo Project have eliminated Colorado squawfish in the <br />upper San Juan River, both from the reservoir basin as well as from several miles of river <br />downstream of the dam, <br /> <br />Extreme fluctuations occurring within t~e framework of a natural annual hydrograph may <br /> <br />5 <br />