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EXECUTIVE SUMMARY Habitat use data for Colorado squawfish were obtained by tracking radio implanted adult fish during July through October, 1996 and July through September, 1997. In addition to the ten Colorado squawfish, five northern pike and five channel catfish were also tagged and located on a biweekly basis. All fish were monitored from River Mile (RM) 77 upstream to RM 138. Colorado squawfish used pool habitat the majority of the daylight time that they were observed in the field. Movement from one pool to another through riffles was documented, however, only one fish remained in the riffles during an observation period. Colorado squawfish moved during the late evening to near midnight for what appeared to be feeding within the local habitat where they were first monitored on the 24 hour observations. No fish during those 24 hour observations was seen moving through a riffle section in 1996 but moved actively within a longer pool or run habitat. During the course of the study in 1996 one Colorado squawfish moved upstream approximately 7 miles. That same fish moved 6 1/2 miles downstream to near the point of initial capture by the end of the study. This fish moved through numerous shallow riffles and one diversion structure during the lowest flows of the year. A second Colorado squawfish was noted to move 5 miles downstream and remain in that downstream location for the study period. In 1997, one Colorado squawfish moved upstream approximately 45 miles during the baseflow period. Channel catfish used pool habitat primarily and run habitat secondarily. Most of those fish remained within the same river mile of contact but two had moved approximately 4 miles downstream at the end of the study in late October, 1996. Northern pike had less movement than any of the other species. They did show movement during 24 hour periods that were similar to Colorado squawfish with movement activity peaking after dusk and in late evening to midnight. They did move from a stationary location upstream and then back downstream to the location where first observed. Most of the northern pike stayed within the same river mile where the initial capture and tagging took place and did not move outside that area. Most movements were less than '/2 mile but they did move from pool through a riffle to a pool during the course of the study. The results of the radio telemetry show that Colorado squawfish in the Yampa River exhibited two distinct activities during daytime and nighttime observations. The fish appeared to be foraging after sunset and moved actively within a habitat or moved to a suspected foraging location. These data show that the Colorado squawfish do show distinctly different habitat use patterns between day and night. Therefore, any flow recommendations for the base flow period should address the habitat use requirements for resting and active behaviors. Determination of the cause of movement (e.g. feeding) could help refine the flow recommendations. If the movement is a feeding behavior, an understanding of the response of the forage species to flows also is important. Final Report - Colorado squawfish habitat Page v Miller Ecological Consultants, Inc. December 17, 1997