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To verify these conclusions obtained from the SI curves the optimum depths and velocities are compared to the mean microhabitat values reported in Tyus, Jones and Trinca (1987; Table 4). According to these authors, adult Colorado squawfish occupy a variety of habitats with mean depths and velocities of 1.Sm (5.9 ft) and 0.25 m/s (0.82 f/s), respectively. They are found predominately in eddies and runs along shorelines, over sand and silt substrates. In comparison the SI curve suggests an optimum velocity of 0.00 f/s, which is slightly lower than that observed. The breeding adults deposit and fertilize eggs on cobble bars with mean depths and velocities around 3.09 ft and 1.58 f/s (Tyus et. al 1987). This is slightly deeper and slower than the optimum previously stated. The razorback sucker uses main channel habitat in depths ranging from 0.6 to 3.4 m (1.97 to 11.16 ft) and are most common in runs near shore in spring, and on mainchannel sand bars composed of unconsolidated coarse sand in summer. Water depths on the sand bars were usually less than 2 m (6.56 ft) with an average water velocity of 0.5 m/s (1.64 f/s). In general these habitat descriptions coincide with the depth/velocity ratings represented by the SI curves for razorback suckers. According to Bovee (1982), when field observations do not verify the conclusions of the SI curves in question, it is customary to modify the curves to reflect the habitat selection. Thus for comparison the SI curves were adjusted to include the mean depths and velocities observed by Tyus, Jones and Trinca. It is assumed that the means observed represent optimum habitat, and therefore, they have been assigned a rating of one. It is likewise assumed that as long as a minimum depth is maintained, depth will not influence habitat selection. Morelikely a species will 13