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<br />2 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />J <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />humpback, and bony tail are designated as endangered species under the <br />Endangered Species Act, whereas the razorback sucker is extremely rare but not <br />yet so designated (Behnke and Benson 1983). Razorback sucker is considered <br />endangered by the State of Colorado, however. These fishes are classified as <br />members of the taxonomic groups Cyprinidae and Catostomidae, the minnows and <br />suckers, respectively. <br /> <br />Formerly the major piscavore of the Colorado River system, Colorado <br />squawfish might have once attained lengths of 1.5 m and weights of 30 kg <br />(Behnke and Benson 1983). The diet of squawfish longer than about 200 mm TL <br />consists almost entirely of other fishes (Vanicek and Kramer 1969). Early <br />white settlers called the Colorado squawfish "Colorado River salmon,1I IIwhite <br />sa1mon,1I and several other similar names, perhaps because the seasonal <br />aggregations of migrating fish in tributary streams and below upstream- <br />movement barriers evoked images of Atlantic salmon Salmo salar or Pacific <br />salmon Onchorhvnchus spp. Early records suggested that the squawfish was <br />distributed throughout the Colorado River and most of its major tributaries <br />(see review by Seetha1er 1978). However, Colorado squawfish now occur only in <br />the upper Colorado River basin of Utah and Colorado. <br /> <br />The humpback chub did not become known to science until 1946 (Miller <br />1946) and little is therefore known of its historic distribution. <br />Contemporary humpback chub in the upper basin inhabit turbulent, deepwater <br />areas--primarily in canyons. Because such areas can be good sites for the <br />placement of dams, it is speculated that much of the former humpback chub <br />habitat in the lower basin was lost when early Colorado River dams were <br />constructed. Such speculation is supported by the similarities in gross <br />physical characteristics between the humpback chub habitat in the upper basin <br />today and that which was lost from the lower basin. The Black Rocks and <br />Westwater Canyon areas of the Colorado River--one and 10-mi1e-10ng river <br />reaches near the Utah-Colorado border--contain the largest known <br />concentrations of humpback chub in the upper basin (Valdez and Clemmer 1982). <br />Populations may also occur in Gray Canyon of the Green River, in the lower <br />Vampa River (a tributary to the Green), and in Cataract Canyon of the Colorado <br />(Tyus et al. 1982a and references therein). A relatively large population of <br />humpback chub occurs in the lower Little Colorado River of the lower basin <br />(Kaeding and Zimmerman 1983). <br /> <br />The Colorado River basin occupies much of the arid southwest, an area <br />rich in natural resources. Development of these resources and the influx of <br />people that naturally accompanies such development, as well as other factors, <br />have created a significant demand for water and conflicts among its possible <br />uses. Because Colorado squawfish and humpback chub are scarce and the range <br />of the humpback chub is especially limited, their populations are believed to <br />be particularly vulnerable to the negative effects of man-induced changes in <br />their environment. Under the provisions of the Endangered Species Act, <br />endangered species designation dictates that Federal agencies involved in <br />resource-development projects must not take actions that are likely to <br />jeopardize the continued existance of endangered species. Proposed <br />developments that knowledgeable authorities believe would reduce populations <br />of endangered species must be modified or canceled, unless the project <br />sponsors obtain an exemption from the Endangered Species Act by the Endangered <br />Species Committee. Thus the presence of an endangered species can greatly <br />influence the development of natural resources. This has been a particularly <br />