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. DRAFT . column velocity does not adequately describe the velocity at the fish Jocation. Perhaps the 0.8 velocity reading is more accurate at depicting velocity zones used by the fish. Perhaps we need to use velocity as a dependent variable that drives the process once a minimum depth is satisfied. Furthermore, the fish are using areas of low velocity that do not reflect the average channel velocities, and therefore provided a distorted view of flow needs that maximize habi tat. IFIM would best serve its purpose by relating fish habitat use to average river channel conditions. If it is possible to incorporate these considerations into IFIM, the method is of value in assessing flow needs in this project. Otherwise, the assessment will have to rely heavily on habitat use and movement in response to changes in flow stage. . 7.1.1 Habitat SUitability Index Curves . The HSI curves are presented as 32 figures which graphically represent various partitions of data for depth, velocity, and substrate used by each of the two fish species. Figures 22-27 represent depth, velocity, and substrate used by Colorado squawfish and razorback sucker under ice-free conditions in year 1 (1987), ice-free conditions in year 2 (1988), and under ice cover in year 2. Figures 28-30 represent a pool of the depth, velocity, and substrate data for fish in ice-free water by species. The remainder of the figures 31-43 represent habitat variables by species for year 1 (1987), year 2 (1988) ice- free, year 2 under ice, and a pool of year 1 and 2 data for ice-free conditions. Each histogram in figures 31-43 is of the raw data with the curve of best fi t superimposed. Also presented wi th each hi stogram is the documentation for the HSI curve. . . 7.1.1.1 Colorado Squawfish . During year 1, a comparisons of 2-hour vs 24-hour monitoring showed no difference in depth, velocity or substrate types used. This meant that observations of the fish during a randomly selected 2-hour period of the day represents habitat used by the fish during the day and night in the winter. Also during year 1, a comparison was made between habitat measurements taken at the fish location and measurements taken one meter toward the shore (in) and one meter away from shore (out). Although depth and velocity were not significantly different between fish location and one meter on either side, substrate type did differ significantly. Also, although mean column velocity (at 0.6 depth) did not differ, all mean velocities and bottom velocities were lowest at the fish location. This suggests that fish were seeking areas of reduced veloci ty between areas of high velocity. oi ffe rences in the distribution of substrates also indicate that the fish may be occupying microhabitats with very different adjacent flow regimes. . . Depth The raw frequency histograms for depth utilization for the 1987 and 1988 data wi thout ice and the 1988 data with ice are contained in Figure 22. Summary statistics for each data partition are contained Table 6. . 36 .