2013-03-06_REVISION - C1992081 (6)

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Rivers have demonstrated downstream distribution of young Colorado squawfish from known spawning areas (Archer et al. 1986; Haynes et al. 1985). Miller et al. (1982) also found that young -of -year Colorado squawfish, from late summer through fall, preferred natural backwater areas of zero velocity and less than 1.5 -foot depth over a silt substrate. Juvenile Colorado squawfish habitat preferences are similar to that of young -of -year fish, but they appear to be mobile and more tolerant of lotic conditions away from the sheltered backwater environment. Information on radio - tagged Colorado squawfish that have been observed during fall suggests that fish seek out deepwater areas in the Colorado River (Miller et al. 1982), as do many other riverine species. River pools, runs, and other deep water areas, especially in upstream reaches, are important winter habitats for Colorado squawfish. Very little information is available on the influence of turbidity on the endangered Colorado River fishes. It is assumed, however, that turbidity is important, particularly as it affects the interaction between introduced fishes and the endemic Colorado River fishes. Because these endemic fishes have evolved under natural conditions of high turbidity, it is concluded that the retention of these highly turbid conditions is an important factor for these endangered fishes. Reduction of turbidity may enable introduced species to gain a competitive edge which could further contribute to the decline of the endangered Colorado River fishes. Colorado squawfish Activity in the 15 -mile Reach The Grand Valley area is occupied year round by Colorado squawfish. The 15 -mile reach is the section of river between the Grand Valley Diversion and the confluence with the Gunnison River. It has been identified as important habitat for Colorado squawfish. Migration Radio - telemetry studies show upstream and downstream movement of adult Colorado squawfish in the main stem Colorado River. The most dramatic movement was exhibited by fish implanted with a radio transmitter at Gypsum Canyon in upper Lake Powell on April 5, 1982. The fish was contacted next in the lower Cataract Canyon area on July 9, 1982. The next contact was made above the Black Rocks area of Ruby Canyon, some 160 miles upstream. The movement was accomplished in 41 days and is believed to be related to spawning. At the end of September 1982, this fish was located on the Colorado River in the vicinity of Clifton, Colorado (river mile 178), nearly 200 river miles from its furthest documented downstream location. Other radio - tagged fish in the Colorado River have not displayed such dramatic migratory behavior. Radio - telemetry studies conducted by the Colorado River Fishery Project (Fishery Project) from 1982 to 1985 (Miller et al. 1982; Archer et al. 1986), which focused on upstream reaches of the Colorado River