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The small size of the fish module and the absence of any sharp projections was perhaps responsible for the lack of irritation. It was concluded that fish behavior was not substantially affected by the transmitter after an initial recovery period, and that the two movement patterns were associated with differences in sexual maturity noted earlier. The Colorado squawfish radiotagged in 1980 exhibited three behavior patterns apparently related to different causes. Fish No. 001 was in poor condition and was recaptured. Its steady downstream movement was ,• indicative of this poor health. Colorado squawfish No's 028 and 165 exhibited an upstream movement in June (Fig. 3); however, this behavior changed in July, with both fish initially moving downstream. This high mobility during the spawning season was believed to be related to spawning behavior. Colorado squawfish No's 064 and 060 remained relatively stationary at their respective points of initial capture (Fig. 4), which was apparently related to a lack of sexual maturity. 1981 Program The radiotelemetry study was expanded in 1981 to include the Yampa and White rivers in addition to the Green River. Nine Colorado squaw- fish were implanted with radio modules in the Green River in 1981 (Table 2). Contact was maintained with only two Colorado squawfish, 079 and 525, on a continous basis throughout the 1981 season. Fish No. 079 was probably immature (421 mm) and remained stationary from April through July, when contact was lost. Fish No. 525 was a mature fish (614 mm) that moved 161 km upstream and ascended the lower Yampa River in late June (Fig. 5). The fish was then relocated in the lower Yampa Canyon on July 2-4, where 34 ripe male and spent female Colorado squawfish were collected. It then moved back downstream and was relocated at its point of capture at Ouray, Utah on July 14. One other Colorado squawfish, No. 243, exhibited similar upstream movement in June, but contact was lost June 24 (Fig. 5). Contact with fish No's 170, 204, 230 and 286 was lost soon after implantation. Fish No. 170 remained stationary and contact was lost in July. It is probable that its stationary existence reflected a lack of reproductive maturity, since this fish was only 471 mm in length. Fish No's 204, 230 and 286 were lost before long distance movement occurred in other adult Colorado squawfish in mid to late June. Seven Colorado squawfish were surgically implanted with radio modules in the Yampa River in 1981 (Table 2). In late June, the radio- tagged fish began moving downstream from their original points of capture and in early July were relocated in the lower 32 km of Yampa Canyon (Tyus et al. 1982). By late July (Fig. 6) all the radiotagged fish had subsequently left the lower Yampa River. Six of these fish were relocated, generally at the same area of initial capture . Found in association with these fish at RK 26.4 (RM 16.5), was one Colorado squawfish radiotagged in the lower Green River near Ouray, Utah (RK 397), which returned to the lower Green River in late July. 10