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in the early summer months. This type of flow regime would have most signifi- <br />cance during normal or below average water years. As an example, the water <br />year 1976 was below average and the high point during early summer was in- <br />adequate to form backwaters of any substantial size. <br />RAZORBACK SUCKER <br />The life history cycle of the Razorback sucker closely parallels that of <br />the Colorado squawfish, and the period of decline in numbers is similar. <br />However, razorbacks can be considered presently more common in the study area. <br />Migration barriers do not seem to have posed a threat to the existence of this <br />fish. The razorback may have more of a direct threat from competition by <br />introduced species of fish. There is the usual coiiipetition for food and space, <br />but in addition, the razorback readily hybridizes with the introduced species <br />of suckers. According to Wiltzius (1976) the Curecanti Project altered con- <br />ditions downstream sufficiently enough to favor the introduced estern white <br />sucker, and',"estern longnose sucker. Both of these species, along with the <br />native endemictlannelmouth sucker and ?luehead sucker, are of the genus <br />z. <br />Catostomus and hybridize readily with the razorback. The resulting competition <br />for spawning bed 1 along with increased hybridization, may be a significant <br />factor influencing the decline of these fish. <br />Humpback Chub <br />The Humpback chub is perhaps one of the rarest fish in Colorado. To <br />date, they have been found only in one location in the state of Colorado. This <br />is in the Black Rock area of the Colorado River about 12 miles upstream from <br />the Colorado/Utah state line. Very little is known about this species, but <br />if it is to be saved from extinction, work should be commenced in the very <br />near future. <br />(31)