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340 McADA AND KAEDING UTAH ? COLORADO N i Black Rocks Grand Palisade Junction d Westwater 6 297 7 0 40 80 Canyon . K 201.1 275.1 7 Kllometere 5 i 8 4.0 1840 Gunnison Colorado 154.5 I River River 4 Dolores 3 River 114.2 1 Gree 75.6 ? 1 Flaming Gorge n \M oab Reservoir River Yam a Ri 2 1 Green to River River Colorado Cataract River Gunnison Canyon I River 0 1 1 Dolores -26.0 River Lake Powell -52.0 I Lake study Area Powell FIGURE 1.-Colorado River study area. Bold numbers designate reaches; decimal numbers are distances in river kilometers from the confluence of the Green and Colorado rivers or Gunnison and Colorado rivers. TL is total length (mm) at time of collection and AGE is accumulated days since hatching. We used only larvae smaller than 22 mm TL in these anal- yses. Marsh (1985) reported that the median in- cubation period for Colorado squawfish embryos held at 20°C was about 102 h; therefore, we esti- mated the spawning date by subtracting 4 d from each hatching date. Nesler et al. (1988) have con- firmed the validity of this technique. Because sample sizes were small, we pooled Colorado squawfish larvae from paired, consecutive reaches when estimating spawning dates. Water temper- ature and discharge data were taken from a U.S. Geological Survey stream gauge at the Utah-Col- orado border. Radiotelemetry.-Movements of adult Colora- do squawfish were followed by radiotelemetry. Fish were collected from each of the study reaches by electrofishing and with gill and trammel nets. No sampling was conducted in reach 2. Most collec- tions were in April or May before the onset of spawning. Because sex of nonbreeding adult Col- orado squawfish is difficult to determine by ex- ternal characters, we were unable to sex most fish. After total length and weight were measured, we anesthetized Colorado squawfish longer than 440 mm and surgically implanted radio transmitters (9-20 g; battery lives, 6, 10, or 18 months), fol- lowing procedures outlined by Tyus and McAda (1984). Radio-tagged fish were released near their capture sites within 2 h of implantation. Hatch- ery-reared Colorado squawfish stocked into the Colorado River in 1980 (Valdez et al. 1982) were identifiable by their Carlin dangler tags; none of the four hatchery fish we encountered were given a radio transmitter. Searches for radio-tagged fish were made by boat about every 2 weeks from April to October and weekly during the presumed spawning season. Tracking was not conducted from November to March. Fish locations were determined to the nearest 0.1 km along the river. Maximum fish dis- placement from the release point during the esti- mated spawning period (spawning displacement), maximum displacement from the release point during the entire monitoring period (maximum displacement), and displacement from the release point at last contact (final displacement) were compared among river reaches and among fish in 100-mm size-classes by analysis of variance (ANOVA). When a fish occupied more than one reach during the estimated spawning period, the