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SUMMARY A total of 31 Colorado squawfish were implanted with radio modules in the Green, White and Yampa rivers in 1980 and 1981. Only 16 indivi- duals were tracked longer than 3 months. Radio module failure, poor radio reception and the high mobility of Colorado squawfish were potential factors influencing success of the tracking effort. Two movement patterns were observed in the implanted Colorado squawfish, sedentary and highly mobile. Total distance moved by 6 sedentary fish averaged 18 km; total distance moved by 10 mobile fish averaged 245 km. The difference in behavior by these two groups was linked to sexual maturity, with mature fish undertaking spawning migrations and hence being more mobile. Local, short-term movement patterns were also studied but the results were largely inconclusive. Diel rhythm either did not exist or variations between the two years and three rivers studied masked real differences. Colorado squawfish were observed predominately in shoreline habitat and were associated with sandy substrate, but were also observed in eddy, run, backwater and pool habitats over silt, boulder, rubble and gravel substrates. Habitat and substrate use varied between river systems and time of year. Water depths and velocities recorded at ob- served locations of Colorado squawfish indicated the fish selected depths and velocities averaging 1.4 m and 0.2 m/s for the Green River, 0.9 m and 0.1 m/s in the Yampa River and 0.7 m and 0.5 m/s in the White River respectively. Comparisons between habitat, substrate, water depth and water velocity measurements recorded for radiotelemetered Colorado squawfish were compared with the same information obtained at the point of capture of Colorado squawfish collected with electrofishing, trammel nets and seines. An analysis of these data indicated close agreement between habitat preference data obtained by the two methods. Minor departures in habitat preferences obtained indicated that radiotelemetry techn-iques were more representative, since the fish were not disturbed and 24 hr. data were obtained. Spawning habitat was located in Yampa Canyon in 1981, when seven radiotagged fish moved downstream in the Yampa River and one radiotagged fish moved upstream from the Green River to reach the spawning grounds located between RK 8 and RK 30. Collections of ripe adults and larvae, and observations of fish behavior confirmed this site as a spawning area. Radiotagged fish entering the lower Yampa Canyon returned to their former upstream or downstream locations after spawning. These movements indicated a homing ability, for which the mechanism is unknown. A physical characterization of the spawning habitat indicated the Colorado squawfish spawned at 22% temperature over rubble substrate. Water depths, and water velocities at the primary site studied (R K 26.4) ranged from 0.9 to 2.1 m depth and 0 to 0.1 m/s velocity. 35