Correspondences Concerning Upper Colorado Biological Opinions 1993

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Elizabeth Estill, Regional Forester 8 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 Sguawfish 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 -1985 (Miller et al. 1982; Archer et al. 1986), which focused on upstream reaches of the Colorado River in and around the Grand Valley, provide the best indication of use of the 15 -mile reach above the confluence of the Gunnison River at one time or another during the field season. Movement of these fish during a field season was generally limited to 25 -30 miles. During 1986, the Fishery Project radio telemetered three adult Colorado squawfish collected from the 15 -mile reach above the Gunnison River in June (Kaeding and Osmundson 1987). The fish exhibited a diversity of localized movement but spent a major part of the next 6 months in the reach upstream of the Gunnison River. Two remained in the reach throughout the estimated spawning period. Spawning Activity A suspected prespawning aggregation of adult Colorado squawfish was observed by Fishery Project personnel at river mile 178.3 in the 15 -mile reach above the Gunnison River confluence in mid -July 1982. In the first observation, three radio - tagged fish were tracked to one riverine pool area, and nine