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- ._~~ - -. --- -- --~__~_ -- ---~._----~-~~=-.__--"""".~~_"":""...l.._.",. - _~ "'.'-.-..",......'-~ ,.......- --.~IL...,,'~... 20 from 1,430 to 1,381 ft3/s at these sites may be attributed to the chronological order of these flows. Backwaters at 1,381 and 1,101 ft3/s were allowed to form during a gradually descending hydrograph. The 1,430 ft3/s flow was obtained immediately after the lowest flow of the season (approximately 1,000 ft3/s). Furthermore, this flow was not allowed to stabilize and only occurred for one day, which very likely affected backwater availability and isolated pool formation. The Ouray and Sand Wash sites had more backwater area at slightly higher flows (1,773 and 1,687 ft3/s). Closer analysis of individual backwaters at Ouray indicated that a few extremely large backwaters (5,000-10,000 m2) atn 1,687 ft3/s did not occur at lower flows; therefore, backwater area was much less. Researchers have not determined which is more important for young Colorado squawfish: backwater area or backwater number. If backwater habitat area is directly correlated to Colorado squawfish young-of-the-year abundance, then backwater area would be more important. However, the flows recommended above maximized both backwater area and number. RM 200 to 280 of the Green River are considered good Colorado squawfish nursery habitat (Tyus et ale 1987), which include the Ouray and Sand Wash sites. The linear regression results indicate that flow has no significant effect on backwater habitat at these sites. This relationship, in part, may explain why these sites are more important to young Colorado squawfish than the Island Park and Jensen sites. As flows from Flaming Gorge Dam travel downstream, peak fluctuations are attenuated and may have less impact on backwater availability. Flows at the Mineral Bottom site are difficult to control because of the numerous tributaries entering the Green River downstream from Flaming Gorge Dam. Because the Green River from Mineral Bottom to approximately the confluence with the Colorado River is an important nursery area for Colorado squawfish, future studies should be conducted to determine the effect of recommended flows at the Jensen gauge on sites in the lower river. During the late summer tributary flows are relatively stable and have a minimal effect on the Green River flow. Consequently, flows measured at the Jensen gauge during this time period should be closely correlated to flows occurring at Mineral Bottom and the resulting backwater habitat could be quantified. It is obvious from our data that sustained flows above 1,773 to 2,423 ft3/s have a detrimental effect on backwater development under the study conditions. Tyus et ale (1987) found marked decreases in nursery (backwater) habitat with high flows and reported a decrease in the Colorado squawfish young-of-the-year catch rate as flows in the Green River were increased. If this situation occurs during the primary nursery season, the growth and survival of Colorado squawfish young-of-the-year could be adversely effected. If the needs of Colorado squawfish in the Green River are to be considered, flows from Flaming Gorge Dam should be controlled during the late summer and the following winter. Upon completion of consultation with the Fish and Wildlife Service, including the Biological Opinion for the operation of Flaming Gorge Dam, it is recommended that