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<br />, <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />19 <br /> <br />Field studies conducted over the past several years by the Service (see above) <br />document the use of the IS-mile reach by several life stages of Colorado <br />squawfish (i.e., adults, larvae, postlarval young-of-year). The Upper <br />Colorado River Basin Biology Subcommittee (1984) identified RM 170-180 of the <br />IS-mile reach above the Gunnison confluence as a "suspected Colorado squawfish <br />spawning area." This determination was based upon: (a) the collection of <br />ripe male and female fish in the reach above Gunnison: (b) the observation of <br />radio-tagged fish in this reach during the spawning season; (c) the occurrence <br />of larvae in and downstream of the reach; and (d) the availability of suitable <br />physical habitat conditions in the reach. <br /> <br />At certain flow regimes, the IS-mile reach above the Gunnison confluence has <br />all the necessary physical components to support spawning (i.e., cobble <br />substrate, riffles adjacent to deep pools). Field studies of the confirmed <br />spawning sites in the Yampa and Green Rivers indicate that Colorado squawfish <br />use this type of habitat for adult staging and deposition of eggs. In <br />addition, water temperatures in the IS-mile reach do reach temperatures <br />conducive to Colorado squawfish spawning. <br /> <br />Numerous natural springs and seeps occur from Mancos shale cliffs throughout <br />the reach. Field observations of the two known spawning sites in the Green <br />River basin suggest that Colorado squawfish spawning may be correlated with <br />areas that receive fresh water from seeps (Tyus and Jones, 1985). <br /> <br />Adult Colorado squawfish also utilize the IS-mile reach on a year-round basis. <br />Catch rates of adult Colorado squawfish in the IS-mile reach during the spring <br />and fall have been twice that found in the adjacent 18-mile reach just <br />downstream of the Gunnison River confluence (see Table 7). In addition, <br />ongoing radiotelemetry studies indicate that Colorado squawfish continue to <br />frequent the reach during the winter. <br /> <br />The IS-mile reach is actively used by Colorado squawfish throughout the year <br />for a variety of purposes (spawning, wintering, general adult use, etc.). <br />This use is occurring in spite of the fact that phYSical habitat conditions <br />are degraded by low flows, especially during the late summer. The Service <br />believes that these data point to the need to protect existing adult habitat <br />conditions and to enhance habitat conditions for Colorado squawfish spawning <br />and recruitment during the months of July, August, and September. <br /> <br />HUMPBACK CHUB <br /> <br />Two major populations of humpback chub (Gila ~) occur in the upper <br />Colorado River at the Black Rocks area of Ruby Canyon (RM 135-137) and in <br />Westwater Canyon (RM 116-124). In addition, a small population of suspected <br />humpback chub X roundtail chub hybrids occurs in DeBeque Canyon. These chubs <br />are thought to be most concentrated near RM 196. but are known from less than <br />10 specimens collected in that area. <br /> <br />In the Colorado River, according to recent collection efforts. humpback chub <br />typically inhabit sections of river that are narrow with jettied flow. <br />Turbulent flows in these narrow areas during humpback spawning may serve to <br />