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<br />According to Bovee (1982), when field observations do not verify the <br />conclusions of the SI curves in question, it is customary to modify the curves <br />to reflect the habitat selection. Thus for comparison a second set of SI <br />curves were developed to include the mean depths and velocities observed by <br />Tyus, Jones and Trinca. It is assumed that the means observed represent <br />optimum habitat, and therefore, they have been assigned a rating of one. It <br />is likewise assumed that as long as a minimum depth is maintained, depth will <br />not influence habitat selection. More likely a species will move up and down <br />in the water column until a suitable velocity is found (Figures 4 and 5). <br /> <br />Table 4. <br /> <br />List of the optimum and mean depth and velo6ity microhabitat <br />implied from the SI curves for Colorado squawfish and razorback <br />suckers compared to the mean values observed by Tyus, Jones and <br />Trinca (1987). <br /> <br />------------------------------------------------------------------------- <br /> <br />SI curve value <br />DeDth 1f1l Velocity (ft/sl <br /> <br />Observed value <br />DeDth eft) Velocity (ft/s) <br /> <br />0.82 <br />1.58 <br /> <br />No Data <br />1.64 <br /> <br />Using the modified SI curves the Colorado squawfish have a minimum optimum <br />depth of 5.18 with velocities between 0.00 and 0.82 ft/s, and the depositional <br />life stage has an optimum depth at 2.04 ft and velocity between 1.58 and 2.27 <br />ft/s. The optimum depth for razorback sucker is at 5.08 ft with velocities <br />between 0.00 and 0.34 ft/s in May and June, and 3.44 ft with velocities <br />between 1.64 and 1.68 ft/s from July to August. <br /> <br />During the development of the curve sets (Valdez et al. 1987), a rating from A <br />to F (A being the highest), was assigned to each curve as a measure of the <br />relative confidence the biologists had in each curve set. The rating was an <br />indication of the relative accuracy of the SI curves to depict microhabitat <br />use. The curve set for Colorado squawfish adults (size 5; 400+ mm) was <br />assigned a confidence rating of "A" for the depth, velocity and substrate <br />curves. The curve set for the deposition life stage was assigned a "C-" <br />because of the small sample size (n=21) and limited number of spawning sites <br />from which the data were collected. The razorback sucker curve sets were both <br />given a "C" rating, because of small sample size (n ranges from 11 to 32). <br />The ratings given each curve by the panel of species experts serve as a <br /> <br />, <br />i <br />I <br />1 <br />~ <br />I <br /> <br /> <br />i <br /> <br />11 <br />