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MOVEMENTS OF COLORADO SQUAWFlSH 1039 TABLE I.-Dates and river conditions when radio-tagged Colorado SQuawfish began spawning migrations in the Green and Yampa rivers, 1981-1988. N= number of radio-tagged fish. Initiation of migration Annual Dateb Discharge (m3/s)C Water temperature eC)c Year flow" N Mean Range Mean Range Mean Range Green River 1981 Low I Jun 14 163.3 21.0 1982 Ave. 2 Jun 25 Jun II-Jul 9 275.7 168.7-325.5 17.6 15.(}"'20.0 1983 High 4 Jul12 Jul 2-Jul 27 474.4 294.3-628.3 18.4 15.5-20.5 1984 High 8 Jun 28 Jun 22-Jul 5 442.1 302.8-718.8 14.6 11.2-18.5 1985 High 8 Jun 9 May 23-Jul 6 268.8 123.7-430.2 18.3 14.(}"'22.0 1987 Ave. 5 Jun 7 May 31-Jun 19 115.5 83.8-149.4 1988 Low I Jun 14 235.2 Yampa River 1981 Low 7 Jun 8 May 27-Jun 20 121.I 33.6--171.8 14.9 12.5-18.5 1983 High 7 Jun 19 Jun 13-JulI2 240.7 127.4-322.6 13.8 9.2-17.3 1988 Ave. 5 Jun 19 Jun 9-Jun 30 129.8 93.4-193.1 15.8 13.8-19.4 a Designation based on mean annual flow. Ranges of means: Yampa River, 43-78 m3/s; Green River, 95-165 m3/s. Ave. = average flow. b Based on first and last departure of radio-tagged fish to each spawning ground. c Data are based on daily averages during range of departure dates (U.S. Geological Survey records). -. year was negatively correlated with the date of the peak flow (r = -1.0, P < 0.01 for Yampa River; r = -0.8, P < 0.03 for Green River); that is, earlier peak flows were associated with longer in- tervals before migration occurred. The date ofav- erage annual migrations occurred 27.7 d (range, 2-42; N = 3 years) after peak flow in the Yampa River, and 28 d (range, 4-50; N = 7 years) in the Green River. Migration was associated with water temperatures of 90C or more (Table 1), but tem- perature-response correlations were not signifi- cant for the few years that data were available (r = -0.8, P = 0.40, N = 3 years for Yampa River; r = -0.7, P = 0.1, N = 5 years for Green River). Migrating Colorado squawfish were tracked to specific spawning locations in Desolation-Gray canyons and Yampa Canyon during summer. These fish moved an average of 140.7 km (range, 32-373 km); fish migrating to Gray Canyon (N = 26) moved an average of 172.6 km (range, 32-302 km) and those migrating to Yampa Canyon (N = 37) averaged 118.4 km (range, 40-373 km). Downstream migrants were most prevalent, and were observed in 76.2% of spawning migrations. Most radio-tagged fish (N = 22) that arrived at the Gray Canyon spawning site (RK 246-318) moved downstream to reach it and averaged dis- tances of 194 km (range, 48-302.4 km). Two came from the White River, one from the Duchesne River, and the remainder from the Green River. Four fish moved 54.8 km (range, 32-92.8 km) upstream in the Green River to reach Gray Can- yon. Of the fish migrating to Gray Canyon, 23 (88.5%) were located in a 4-km reach (RK 246- 250) during the spawning period. Twenty-four radio-tagged fish moved an aver- age of 113.1 km (range, 52.8-155.2 km) down- stream in the Yampa River, and 11 moved an average of 100.8 km (range, 40-235.2 km) up- stream from the Green River to reach the Yampa Canyon spawning area (RK 7-48). Two fish moved downstream in the White River, then upstream in the Green and Yampa rivers, distances of 186 and 373 km respectively, to reach Yampa Canyon. Many Yampa Canyon fish (N = 37) were located in a 7 -km reach (RK 22-29). Desolation-Gray and Yampa canyons were high-gradient reaches (1.8 m/km drop in stream- bed elevation for both: RK 0-48 in Yampa Can- yon; RK 227-299 in Desolation-Gray canyons), and many migrating fish passed through lower- gradient (0.2-0.4 m/km) sand and silt reaches in the Green River to reach these areas. Some mi- grating fish bypassed areas of apparently suitable spawning habitat enroute to the two spawning ar- eas. Fish migrating downstream in the Yampa River traversed high-gradient, canyon-bound rif- fles of cobble, gravel, and boulder substrates in Juniper, Cross Mountain, and upper Yampa can- yons, and fish migrating upstream from Green River passed similar areas in Split Mountain and Whirlpool canyons. In the Green River, fish passed upper and lower Desolation and Gray canyons to reach the spa w::ir;.,; sic;;. Migrating fish were exposed to freshwater in- flows (about 0.14 mJ/s)from spring-fed tributaries