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did not appear to be in reproductive condition. We found no evidence to indicate that Colorado squawfish spawned in the 15- mile reach during 1986, although such spawning there has been documented by FWS in previous years (Archer et al. 1985). Our capture data for ripe fish in 1986, and those from previous years (Miller et al. 1982), indicate that razorback sucker probably spawn within the 15-mile reach. The capture of a yearling-size squawfish at RM 174.5 was the only such capture in the Grand Valley during the past 10 years. The 15-mile reach appears to be important to adult Colorado squawfish and razorback sucker, as evidenced by catch rates there that are higher than in the adjacent downstream river reach. Adults seem to be most abundant in a 0.6-mile segment (RM 174.4- 175.0) of the 15-mile reach during high water, particularly in two gravel- pit ponds. These fish may have moved into these ponds for a respite from high spring flows, or they may have been attracted to the warm environments that the ponds provide (pond temperatures were as much as 10.5 C warmer than the adjacent river); some of the squawfish captured from one pond were well tuberculated by 3 June, when nearby river temperatures were only 10-13 C. In spring 1987, we will install a two-way fish trap in the mouth of one of these ponds. Use of this trap should allow us to better understand the importance of gravel-pit ponds to Colorado squawfish and razorback sucker. We will continue monitoring movement, microhabitat use, and spawning activities of Colorado squawfish in 1987. Resulting data will be compared with those collected in 1986. Our assessment of winter use of the 15-mile reach by Colorado squawfish is currently in progress. 16