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.---. ~, '. 18 Nonspawning Adult Occurrence Over 60 percent of the adult-size Colorado squawfish collected by the project (Miller et al. 1982, Kaeding and Osmundson 1987) during spring surveys came from the upstream river reach (Table 7). This IS-mile reach appears to be important to adult Colorado squawfish, as evidenced by catch rates there that were twice as high as the adjacent downstream river reach (Kaeding and Osmundson 1987). Adults seemed to be most abundant in a 0.6-mile segment (RM 174.4-175.0) of the IS-mile reach during high water, particularly in two gravel-pit ponds. These fish may have moved into these ponds to feed, rest, or they may have been attracted to the warm, productive environments that the ponds provided (pond temperatures were as much as 10.5 degrees C warmer than the adjacent river). Some of the squawfish captured from one pond were well tuberculated by June 3, when nearby river temperatures were only 10-13 degrees C (Kaeding,pers. comm.). Table 7. Adult-size Colorado squawfish captures from the Colorado River reaches upstream and downstream of the Gunnison River confluence. Year Upstream Reach (RM 186-171) Oownstream Reach (RM 170.9-156) No. caught Size range No. caught Size range (TL, mm) (TL, mm) . 1979 4 495-559 0 1980 1 615 2 670 1981 2 528-572 0 1982 13 556-742 0 1983 0 3 440-718 1984 0 3 556-705 1985 0 5 505-896 1986 13 541-810 6 595-800 Total 33 19 The IS-mile reach above the Gunnison confluence is a wintering area for adult Colorado squawfish. Spring captures of adult fish and recent radiotelemetry studies have indicated that the fish are spending the winter in the reach; however, further study is needed to better define the extent of this use. Discussion and Conclusions . The importance of the IS-mile reach from Palisade to the confluence of the Gunnison River must take into account the fact that the Colorado squawfish is currently endangered and restricted to 25 percent of its original range. The Colorado River subbasin population shows particular signs of further decline; catch-per-unit effort rates for larvae, young-of-year and adult Colorado squawfish are significantly less than for the Green River population (Archer et al. 1986). Additional loss or degradation of remaining habitat will exacerbate the problems the species is currently experiencing in the Colorado River.