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<br />. <br /> <br />. <br /> <br />. <br /> <br />( <br /> <br />optimum habitat suitability. In all of the example streams examined by DOW and BLM, these <br />depths only occur in riflles at the peak of spring hydrograph or duri;:g flocc e"~:1t i:: .esponse to <br />thunderstorms. Given the size and health of the fish populations, BLM and DOW concluded that <br />these species do not require this depth of riffle habitat to thrive in the stream environments unique <br />to western Colorado. This conclusion is not surprising given that dace and sucker species are <br />known to develop distinct genetic populations and distinct physical characteristics in response to <br />flow conditions. <br /> <br />In lieu of this seldom-achieved depth criteria suggested by the curves, BLM and DOW concluded <br />that the 0.2 foot average depth criteria used for salmonids would provide adequate physical <br />habitat for the cool-water species. Achieving the 0.2 foot average depth criteria will mean that <br />some portions of the riffle habitat will be much deeper than 0.2 feet, and we would expect that <br />pool and run habitat would have a much greater average depths than 0.2 feet. Therefore, even if <br />the average riflle depth is 0.2 feet, a large percentage of overall habitat (riffles, runs, and pools) <br />will fall within the range of "suitable" habitat depth suggested by the curves. <br /> <br />Velocity -- As noted above, riffle habitat is important to all of these species, but each prefers <br />differing velocities in the riffle habitat areas. For example, dace prefer moderate to high <br />velocities, while the white sucker prefers low to moderate velocity. In order to not favor one <br />species over another, BLM and DOW concluded that the preferred approach was to protect <br />velocities on the lower end of the optimum velocity range, and then let the natural variation in <br />flows provide the velocities which favor the different species at different times of the year. <br /> <br />The habitat suitability curves suggest the that range of optimum velocity for the adult life stage of <br />speckled dace is 0.75 feet per second to 1.75 feet per second. Optimum velocity for the juvenile <br />life stage is from 0.75 to 1.5 feet per second. Optimum velocity for fry is from 0.5 to 1.25 feet <br />per second. BLM and DOW concluded that 1.0 foot per second velocity criteria would work well <br />for all three life stages of speckled dace. <br /> <br />The critical period for the sucker populations is the incubation stage, which occurs annually <br />during April through August.. The habitat suitability curves suggested velocities ranging from 1.0 <br />to 2.0 feet per second for optimum habitat during this period. BLM and DOW decided that using <br />the 1. 0 foot per second criteria would work for sucker species as well, because the instream flow <br />water rights are designed to protect minimum flows during this period, and aren't intended to <br />protect spring runoff peaks. The natural runoff peaks will provide velocities that are closer to 2.0 <br />feet per second during portions of the April to July period. <br /> <br />Conclusion - The physical habitat requirements of these unique assemblages of species in western <br />Colorado streams is not dramatically different from the physical habitat requirements for <br />salmonids. The factor that produces a different set of species in these streams is water quality, in <br />terms oftemperarure, suspended solids, and dissolved solids. Therefore, BLM and DOW <br />conclude that utilizing the physical habitat criteria developed for salmonids will work well for <br />these streams. Streams with significantly different assemblages of species than those a:lalyzed <br />during chis process should be analyzed separately to determine if the R2Cross model and criteria <br />are applicable. <br />