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<br />SUBADULT HUMPBACK CHUB IN THE COLORADO RIVER <br /> <br />279 <br /> <br />\' <br /> <br />8 10 12 14 16 18 20 <br />Discharge (cms x 1,000) <br /> <br />Figure 7. Change in depth, velocity and cover with discharge for each shoreline type. Data points are not shown to facilitate <br />visualization of trends. Be, bedrock; CB, cobble; OF, debris fan; SA, sand; TS, talus; and VG, vegetation <br /> <br />10 <br />8 <br />6 <br />4 <br />2 <br />o <br />0.60 <br />0.45 <br />0.30 <br />0.15 <br /> <br />0.0 <br />100 <br />80 <br />60 <br />40 <br />20 <br /> <br />o 6 <br /> <br /> <br />Velocity (m/s) <br /> <br />- - -'"":::.- """----~ - - - - <br />~-: -~- <br /> <br />SHORELINE <br />- - VG <br />SA <br />CB <br />- - - DF <br />TA <br />- BE <br /> <br />" <br /> <br />The importance of cover as an attribute of habitat <br /> <br />Numerous studies have demonstrated the importance of cover as a habitat attribute (Fraser and Cerri, <br />1982; Fraser, 1983; Power et al., 1985; Schlosser, 1987). Cover may be important for several reasons. <br />First, fish may seek out cover to avoid light (Lewis, 1969; Cunjak, 1988). This possibility seems likely for <br />native fish of the Colorado River, which evolved under turbid conditions and have been noted as <br />negatively phototactic (Valdez et aI., 1992). Secondly, small fish may find it easier to avoid predation in <br />areas with greater cover (Fraser and Emmons, 1984; Mesick, 1988). The recent introduction of nonnative <br />salmonids, catfish and other piscivorous sport fish has added a substantial source of predation that did <br />not exist historically (Marsh and Douglas, 1994; Valdez and Ryel, 1995). Also, cover is frequently the <br />result of some laterally or vertically emergent object that obstructs flow, thereby providing refuge from <br />high current velocities (Fausch, 1984; McMahon and Hartman, 1989). <br /> <br />.. <br /> <br /> 5 <br /> 4 I <br />0- Pre-dam <br />0 I <br />0 <br />0 <br />.... 3 J <br />x <br />Ul <br />E ( <br />~ 2 <br />CD <br />e> ,/ <br />I'll Post-dam <br />or=. <br />0 1 <br />Ul <br />is <br /> <br /> <br />20 40 60 80 100 <br /> <br />Percent lime less than <br />Figure 8. Flow duration curve of the Colorado River at Lee's Ferry gauge <br /> <br />@ 1998 John Wiley & Sons, Ltd. <br /> <br />Regul. Rivers: Res. Mgmt. 14: 267-284 (1998) <br />