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was made below Westwater in September. The radio transmitters were near the end of their expected battery life about the time contact was lost; however, the possibility that the fish left the study area cannot be ruled out. Movement of radiotelemetered Colorado _UUawfish was closely mon' dur' attem t to locate spawning areas. On July 13 three radiotelemetered fish were found in a small pool in a side channel at Rfi 178.3 near Clifton, Colorado. Trammel nets drifted through the pool collected nine Colorado squawfish including one radio-equipped fish; five of these fish were ripe males. The remaining fish were tuberculated in a pattern believed typical of mature females, but sex products could not be produced when pressure was applied to the abdomen. An additional radiotelemetered Colorado squawfish was subsequently observed in the vicinity of this pool. A large eddy at RM 176 was independently visited by five radio- telemetered Colorado squawfish during the last two weeks in July. A ripe male Colorado squawfish was collected from this location. A radio- equipped Colorado squawfish recaptured from a nearby side channel had a distended abdomen and had gained about 500g in the six weeks since it was released. Although sex products were not expressed from this fish, it was most likely a maturing female. Although an aggregation of ripe male Colorado squawfish is a significant observation, it does not necessarily indicate that spawning occurred in the immediate vicinity. Males of most minnows ripen earlier than females, and they'can move considerable distances after ripening before spawning occurs (Breder and Rosen 1966). We encountered ripe mate Colorado squawfish in WWWA (RM 163.6) one month before the aggregation at RM 178.3 was noted. We implanted two of these fish with radios; one subsequently was found among the group of radiotelemetered fish that constituted the aggregation near R14 178.3 described above. These two fish implanted in WWWA moved 10 miles and 15 miles respectively, during the time they were ripe. Although spawning did not necessarily occur in the immediate vicinity of RM 176.0 or 178.3, it did occur in the Grand Junction area as demonstrated by the collection of larval Colorado squawfish in August. The aggregation of mature Colorado squawfish near Clifton, Colorado occurred when river flows were receding and water temperatures were near 20 C (Figure 5). This 20 C has been shown to be the temperature where Colorado squawfish successfully spawn (Miller et al. 1982). In addition to the radio tracking effort in the Grand Junction area the FWS also conducted similar radio tracking work in the Green River. Green River work was a continuation of 2 years of radiotelemetry and will aid to further define movement patterns and spawning behavior of Colorado squawfish. Eleven adult Colorado s uawfish were radio-tagged and tracked by FWS Ln th Green Rivas dicer n 1982. Collection o a u t fish for tagging began on May 4th and by May 20th eleven fish ranging in - 11 -