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Wick et al. 1985). During winter, adult Colorado <br />squawfish use backwaters (ephemeral along-shore <br />embayments), runs, and eddies, but are most common, <br />and presumably feed, in shallow, ice-covered shoreline <br />areas where large schools of minnows have been <br />observed (Wick and Hawkins 1989). Local <br />nonmigratory movements of adult Colorado squawfish <br />in nonbreeding seasons may be indicative of <br />home-range behavior (Tyus et a1.1987; Tyus 1989; Wick <br />and Hawkins 1989). <br />In spring and early summer in the Yampa River, adult <br />Colorado squawfish were most often located in <br />backwater habitats or flooded bottomlands. <br />Radio-tracking data indicated high use of shoreline <br />backwater habitat in 1981(a low-flow year; 66%, N = b <br />individual fish) and high use of flooded bottomlands <br />during 1983 (a high-flow year; 40%, N = 10). None of <br />the 10 fish located during 1983 were in backwater <br />habitat. Wick et al. (1983) noted that in 1982 (an <br />average-flow year), adult Colorado squawfish used <br />flooded shoreline areas in spring but moved to <br />backwater habitats as the river level dropped. High use <br />of flooded shorelines was also noted for adult Colorado <br />squawfish in the Green River during the 2 high-flow <br />years, 1983 and 1984 (Tyus et ~a1.1987). <br />Adult Colorado squawfish occupied a variety of <br />habitats in mid-to-late summer, but were most common <br />in eddies, pools, runs, and shoreline backwaters, over <br />sand and silt substrates (Fig. 5). Visual observations in <br />shallow water indicated that adults use sheltered <br />microhabitats behind boulders, flooded vegetation, or <br />other cover. During summer, radio-tagged fish were <br />most often located in deeper shoreline habitats, where <br />3b <br />F 30 <br />z <br />2b <br />a <br />w> <br />Vi <br />~~2~ <br />~m <br />ao <br />QQ~a <br />=O <br />~ 'lo <br />Z <br />W <br />U <br />W b <br />a <br />ED PO RI/RU BA RU SH MT MB FB RA <br />HABITAT TYPE <br />Fig. 5. Habitat use byradio-tagged Coloradosquawfish in the <br />Yampa River, June-August, 1981,85, 1987, 1988. ED = <br />eddy; PO =pool; RI/RU =riffle/run < 1.67 m depth; BA <br />=backwater; RU =run > 1.b7 m depth; SII =shoreline; <br />MT =mouth of tributary; MB =mouth of backwater; FB <br />= flooded bottom; RA =rapid. <br />193 <br />161 <br />129 <br />97 <br />64 <br />w <br />w 32 <br />O <br />-~ 555 <br />Y <br />o' <br />523 <br />iY <br />491 <br />~ 458 <br />z <br />~ a27 <br />394 <br />3b2 <br />Fig. 6. Movement patterns of radio-tagged Colorado <br />squawfish migrating to Yampa River spawning grounds, <br />1981-85, 1987, and 1988. Spawning reach is delineated by <br />(-__); 0 =midpoint of calculated optimum spawning <br />period for each year. Adjusted date scale in 28-day <br />increments. <br />movements suggested heavy use of eddy-run interface <br />(Tyus et al. 1987). <br />Spawning <br />Two major Colorado squawfish spawning migrations <br />have been identified by Service biologists in the Green <br />River basin by tracking radio-tagged fish. One migration <br />was discovered in the Yampa River and upper Green <br />River in 1981 (Tyus and McAda 1984), confirmed in <br />1982 (Wick et al. 1983), and again from 1983 to 1988 <br />(Tyus et a1.1987). Movement patterns of fish migrating <br />to the Yampa River spawning reach are presented for <br />1981-88 (Fig. 6). In May and early June, Colorado <br />squawfish began downstream migrations in the Yampa <br />and White rivers and upstream migrations in the Green <br />River to spawn in riffle and pool habitat of the lower <br />51.2 km of the Yampa Canyon (Fig. 4). The only other <br />confirmed Colorado squawfish spawning site in the <br />Green River basin is in Gray Canyon (RK 224-25b) of <br />the Green River (Tyus et a1.1987; U.S. Fish and Wildlife <br />Service, unpublished data). <br />6 <br />0 <br />ADJUSTED DATE <br />