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<br />86 <br /> <br />TYUS AND HAINES <br /> <br /> 48 <br />E 44 0 <br />0 <br />.5 <br />:r: 40 <br />f- <br />(I) <br />~ 36 <br /><( <br />f- <br />0 32 <br />f- <br /> 28 <br /> <br />Y = 46.247 - 0.576X <br />r . -0.565 <br /> <br />40 60 80 100 120 140 160 180 200 220 <br /> <br />5 <br /> <br />Y = 4.730 ' 0.024X <br />r = -0.859 <br /> <br />N <br />E <br />o <br />o <br />:::: <br />ti <br />e; <br /> <br /> <br />(I)" <br />9 <br /> <br />-1 <br /> <br />~ ~ W ~ m ~ ~ ~ = = <br /> <br />STREAMFLOW (m'l.ee) <br /> <br />48 <br /> <br />Y = 50.296 - 0.140X <br />r = -0.810 <br /> <br />44 <br /> <br /> <br />40 <br /> <br />36 <br /> <br /> <br />32 <br /> <br />28 <br /> <br />20 40 60 80 100 120 140 160 <br /> <br />o <br />o 0 <br /> <br />Y = 4.281 - 0.039X <br />r = -0.797 <br /> <br />-1 <br /> <br />-2 <br /> <br />-3 <br /> <br />20 40 60 80 100 120 140 160 <br />STREAMFLOW (m :V.ee) <br /> <br />FIGURE 3.-Regressions of Colorado squawfish mean total length (Y) on mean August-September streamflow, <br />and 10g,.(fish/IOO m2) (Y) and streamflow in the lower (left) and the upper (right) Green River, 1979-1985 and <br />1987-1988. Hows for the lower Green River were measured at the town of Green River, Utah;. flows for the upper <br />Green River were measured at Jensen, Utah. <br /> <br />River within 3 to 15 d after hatching, and who <br />presumed that they were present in a 6-km river <br />reach for only about 1-2 d. We are aware of no <br />age-O or age-l juveniles captured in autumn above <br />the mouth ofthe Yampa River in the last 10 years. <br />Some age-O fish present in our upper Green Riv- <br />er samples could be the result of spawning below <br />the Yampa River. However, we believe that the <br />vast majority, if not all, of age-O Colorado squaw- <br />fish found in the upper Green River are the result <br />of downstream drift from the Yampa River. Ra- <br />diotracking of adults on spawning migrations has <br />not confirmed other spawning locations in the up- <br />per Green River (Wick et al. 1983; Tyus 1985, in <br />press). Drift oflarvae into the Green River is well <br />documented (Haynes et al. 1984; Nesler et al. <br />1988), and summer and autumn concentrations <br />of age-O Colorado squawfish downstream from the <br />Yampa River spawning area suggested down- <br />stream movements. Finally, substrates in most of <br />the upper Green River (from Jensen to Desolation <br />Canyon) are fine silts and sand rather than cobbles <br />and boulders that exist in the known spawning <br />areas. We presumed that spawning would not oc- <br />cur on such substrates. <br /> <br />Although our data are not as extensive for the <br />lower Green River, we presume that a similar pat- <br />tern of larval drift occurs there. Years of radio- <br />tracking migrating adults and collecting ripe fish <br />there have indicated that RK 225-257 is a major <br />spawning area, and no other such area has been <br />confirmed downstream. Larvae were caught in drift <br />nets 8 km downstream (at RK 217) ofthe spawn- <br />ing area, and seining results show summer and <br />autumn concentrations of postlarval Colorado <br />squawfish downstream ofthe spawning area. Thus, <br />data collected at the Green River site support our <br />conclusions drawn from the Yampa River regard- <br />inglarval movement, and it is possible that larvae <br />drifting out of the Yampa River reach nursery <br />habitats in the lower Green River. <br />We were concerned about the validity of using <br />hatchery-derived growth equations for estimating <br />Colorado squawfish spawning dates from total <br />length of fish, particularly for the larger postlar- <br />vae, a concern also expressed by Nesler et al. <br />(1988). Average temperatures in the Green River <br />at mean larval hatching dates ranged from 20 to <br />250C, but the July-August backwater tempera- <br />tures at fish capture averaged 25-280C. Thus, <br />