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344 McADA AND KAEDING TABLE 3.-Spawning displacement, maximum displacement, and final displacement of radio-tagged adult Col- orado squawfish, by reach of release. Spawning Maximum Final displacementa (km) displacementb (km) displacement' (km) Release reach N Mean SE Range Mean SE Range Mean SE Range 1 7 4.2 1.1 0.8-10.0 56.1 43.0 4.0-313.0 48.3 44.1 1.3-313.0 3 13 32.1 8.7 0.0-92.7 44.2 14.2 1.0-193.4 31.1 9.0 0.0-112.5 4 1 46.7 46.7 46.7 5 2 47.4 45.3 2.1-92.6 53.2 39.4 13.8-92.6 53.2 39.4 13.8-92.6 6 20 217 3.5 1.8-58.3 33.1 3.7 7.4-77.1 22.4 5.0 0.3-77.1 7 4 8.0 2.9 1.1-13.0 12.0 2.0 6.4-16.1 4.4 2.7 1.6-12.4 8 3 21.3 19.0 0.8-59.2 24.6 16.9 4.0-58.0 20.6 18.4 0.8-57.3 a Maximum displacement from the release point during the estimated spawning period. b Maximum displacement from the release point during the entire monitoring period. Displacement from the release point at last contact. dominance of movements less than 50 km long by tagged adults in the Colorado River and the widespread distribution of small larvae (6-10 mm TL) support this explanation. Differences in the seasonal movements of adult Colorado squawfish between the Colorado and Green rivers may also be explained by important differences in habitat. Although discharge regimes of both rivers have been altered considerably by upstream dams and water diversions, only the Green River has a large main-stem dam, Flaming Gorge, within the for- mer range of Colorado squawfish. Operation of Flaming Gorge Dam has reduced summer water temperatures of the Green River downstream (Vanicek and Kramer 1969) to the extent that the river now provides suitable habitat for salmonids. At the confluence of the Green and Yampa rivers below Flaming Gorge Dam, summer water tem- peratures of the relatively unmodified Yampa can exceed those of the Green by as much as 10°C (Tyus et al. 1987). The dams and reservoirs of the Colorado River, in contrast, are located in headwater areas far up- stream from historical or current Colorado squaw- fish habitat, and the dams farthest downstream are not operated for peaking power production. However, a comparison of U.S. Geological Survey records for the years 1908-1923 and 1966-1989 showed that these dams have caused a 49% re- duction in average peak instantaneous discharge at the Utah-Colorado border. In addition, the Colorado River has low-head diversion dams that prevent upstream movement of adult Colorado squawfish into their original habitat. These diver- sion dams may have blocked and thereby led to the demise of upstream populations of adult Col- orado squawfish that formerly moved down- stream to spawn, much as Colorado squawfish now do in the Yampa River (Tyus 1985). Such repro- duction might have been important to the main- tenance of viable populations of Colorado squaw- fish in the upper Colorado River. The aggregation of adult Colorado squawfish observed in reach 7 in July 1982 might have been a remnant of a much larger aggregation that occurred historically in the Colorado River. Tyus and McAda (1984) reported that the long- distance movement of radio-tagged Colorado squawfish in the Green River basin was related to fish size and thus to maturity. Small fish (400-500 mm TL) moved little, whereas larger individuals moved extensively. In contrast, we detected no difference in distance moved among the size-class- es of adults. The return of many radio-tagged fish to their release reach (often to within 8 km of their original point of capture) suggests that some Col- orado squawfish home to previously occupied feeding or wintering areas. Wick et al. (1983) and Tyus (1985) similarly observed that many radio- tagged Colorado squawfish returned to points near their original capture locations after the spawning season. Results of this study suggest that the spawning areas for Colorado squawfish are widely distrib- uted along the upper Colorado River and that the seasonal movements of adult fish to these areas are relatively short. However, whether the adult fish have fidelity to particular spawning areas is unknown, as is the consequence of denying them access to such spawning areas. Consequently, we recommend that no additional barriers to the free movement of Colorado squawfish be permitted within the current range of the species. Also, al- though the apparent widespread spawning of Col- orado squawfish in the upper Colorado River sug- gests that spawning habitat is not limiting the