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<br />SUBADULT HUMPBACK CHUB IN THE COLORADO RIVER <br /> <br />277 <br /> <br /> 100 <br /> 80 Reach 1 <br /> 60 <br /> 40 <br /> 20 <br /> 0 <br />.c 100 <br />0 80 Reach 2 <br />~ <br />Q; 60 <br />a. <br />.c 40 <br />u <br />ro 20 <br />t.) <br /> 0 <br /> 100 <br /> 80 <br /> 60 <br /> 40 <br /> 20 <br /> 0 <br /> <br /> <br /> <br />Figure 5. Relative densities of subadult humpback chub among shoreline types in reach I, reach 2 and reach 3. Be, bedrock; CB, <br />cobble; DF, debris fan; SA, sand; TS, talus; and VG, vegetation <br /> <br />Relationship between discharge and habitat condition <br /> <br />The MSLR showed that habitat conditions varied significantly with discharge for certain shoreline <br />types (Table IX). Overall, mean shoreline depth and velocity increased with increasing discharge, whereas <br />mean cover decreased (Figure 6). However, this trend was not consistent among shoreline types. Mean <br />depth and velocity of bedrock, debris fan, cobble and vegetation shorelines tended to increase with <br />increasing discharge, whereas they decreased within sand and talus shoreline types (Figure 7). Total cover <br />within bedrock, talus and debris fan shorelines decreased with increasing discharge, yet total cover within <br />cobble, sand and vegetation shorelines remained constant or increased. <br />When considered in conjunction with changes in the discharge regime, these results suggest that habitat <br />quality has decreased in the post-dam era. A comparison of the flow duration curves for the pre- and <br />post-dam periods show that the temporal distribution of discharge has changed such that mean daily <br />discharges are less extreme more of the time (Figure 8). Prior to dam closure, discharge was less than 140 <br />m3 s - I 20% of the time and less than 225 m3 s - I more than 50% of the time. Since construction of Glen <br />Canyon Dam, flows less than 140 m3 s -1 have occurred only 3% of the time, and flows less than 225 m3 <br />s - I have occurred only 12% of the time. <br /> <br />Table IX. Results of multivariate simple linear regression showing changes in depth, <br />velocity and cover with discharge. DF, degrees of freedom of the numerator and <br />denominator <br /> <br />Source <br /> <br />DF <br /> <br />Wilks' A <br /> <br />F <br /> <br />Discharge (Q) <br />Shoreline (S) <br />QxS <br /> <br />3,55 <br />15, 152 <br />15, 152 <br /> <br />0.539 <br />0.359 <br />0.366 <br /> <br />15.69 <br />4.56 <br />4.46 <br /> <br />P <br /> <br /><0.001 <br /><0.001 <br /><0.001 <br /> <br />@ 1998 John Wiley & Sons, Ltd. <br /> <br />Regul. Rivers: Res. Mgmt. 14: 267-284 (1998) <br />