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I I I I I I I- I I I I I I I I I I I I - 5.0 SUMMARY Numbers of backwaters and densities of young Colorado squawfish have been monitored in the Lake Powell intlow since 1985. During this time dramatic changes in habitat have occurred because of varying lake levels. The elevation of Lake Powell decreased by 80 feet from 3700 feet (full capacity elevation) in June 1985 to 3627 feet in April 1993. This change in lake elevation created major habitat changes in the inflow region. The point at which the Colorado River entered Lake Powell shifted from RM 201.5 downstream to RM 170 (observed April 1993). This effectively extended the flow of the Colorado River by 29 miles into the former lake basin. The numbers of young Colorado squawfish captured in the inflow varied considerably from 1985 through 1993 (Figure 4). From 1985 through 1991, the number of fish captured ranged from 2 to 70. Sampling in April 1993 yielded 84 Colorado squawfish (20 - 96 mm TL). This is the largest number of age-O and juvenile Colorado squawfish captured in the inflow region since sampling beg~ in 1985. - -' -- - .-- -- 20 I EZI No. BACKWATERS . No. SaUAWFISH I 100 80 CJ) 15 '- .c Q) en ...... <<S '+- ~ 60 ~ ~ <<S (.) 10 ::) <<S C- eo 40 (J) . . 0 1 0 Z 5 Z 20 o 85 ~ 88 89 91 92 93 90 8S 87 Figure 4. Number of backwaters and age-O and juvenile Colorado squawfish captured seining in the Lake Powell intlow from 1985 to 1993. Pre-runoff densities of age-O Colorado squawfish were sinillar to densities measured in the Green and Colorado rivers above their confluence during spring 1993 ISMP sampling. Geometric mean CPE for pre- runoff sampling was 1.05 age-O/loom2. This compares with densities of 0.92 age-O/100m2 for 35 miles of the Colorado River above the confluence and densities of 1.03 age-O/100m2 for the lower 120 miles of the Green River (Valdez and Cowdelll994). 13 o