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_ Y t substrate. Other important habitat conditions (e.g., cover) can be included to accurately describe the reach. The Biological Subcommittee should provide their critical critique to the field biologists and the Instream Flow Group so that biological and hydrological data are obtained in a standardized manner. Finally, the models should be tested and validated with empirical data. Description of habitat utilization by the rare fish is difficult because of the river conditions (e.g. deep pools with rocky outcrops, boulders, and uneven bottom and whitewater areas) and because the fish change their use of habitat in response to the river conditions (e.g., adult squawfish apparently use deep pools in the main channel during the winter, move into backwater [flooded] areas that are created by increased streamflow during the late spring - early summer runoff, move to areas with pools or runs with low to moderate velocity as "staging" areas and spawning bars that have rubble or gravel substrate with 1.6 - 5.0 ft/sec flow at depths of 3.4 - 5.0 feet, and return to deep pools in the main channel between August and early October). Measure- ments of some of these habitat conditions (e.g., deep pools) have not been made since the exact location used by the squawfish are not known. Thergfore, it is very clear that all "critical" habitat conditions for all life stages will not be known. However, the models still serve as useful tools if the limitations are understood and accepted. AUGMENTATION OR RECOVERY OF RARE COLORADO RIVER FISH o Determine the feasibility of fish passage facilities and test experimental prototypes under controlled conditions as a management tool to extend the range of rare fish and to enhance populations. Rationale - Dams on the Colorado River have blocked the passage of migrating Colorado squawfish which were observed to aggregate below Flaming Gorge Dam on the Green River and Taylor Draw Dam on the White River. Fish passage facilities would be a nonflow alternative for providing habitat for subadult and adult Colorado squawfish and razorback suckers that are known to migrate. Such structures could also provide a means for these species to become re-established in parts of their former historic range. Considerations - The major consideration is to demonstrate that rare o orado River fish will use fish passage facilities. Careful analysis of existing designs, consultations with engineers who have experience in fish passage, and experimental testing of a prototype fish passage facility should be made to assure that the rare fish could be passed upstream and downstream. Consideration should be given to designing an experimental fish passage facility that could be easily modified or taken down and moved to provide versatility in the structure. The experimental prototype should be tested on low head dams. Fish passage over high 11