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<br />upon whether thi! species is a generalist in its habitat needs or not, river reaches in Colorado <br />designated for bony tail stocking may be revised considerably. <br /> <br />Further, the following species interactions and recovery actions are anticipated: <br /> <br />1) Biomass and production occupied by common carp and other nonnative fish in the Grand <br />Valley may be reduced by control efforts, lessening competitive pressure within floodplain <br />habitats, and perhaps permit expansion of bonytail biomass. <br /> <br />2) With SUcceiiSful establishment of an adult bonytail population, general abundance of other <br />native species may be reduced as a result of some competition. <br /> <br />Achievement of the stocking objective would result in adult populations of at least 4,400 <br />four to six-year-old adult fish in two geographically distinct locations in the Upper Colorado River <br />subbasin. Due to the uncertainties associated with habitat needs of bonytail, specific definitions <br />of their probable distribution and abundance cannot be presented as is being done for razorback <br />sucker and Colorado pikeminnow. Clearly, monitoring will be required to refme the objectives <br />that serve as a starting point. <br /> <br />Reintroduction of bony tail into the upper Colorado River Basin has been assessed by <br />several studies (Chart and Cranney 1992, Meyer 1992, Wydoski 1994, Lentsch et al. 1996). <br />Recommendations included the necessity of reintroduction of bony tail in the wild to detennine it's <br />ecological requirements, but concerns have been expressed about reintroducing bonytail because <br />of the potential hybridization with the other Gila species, especially humpback chub. While <br />acknowledged as a potential risk associated with reintroduction and establishment of bonytail near <br />existing humpback chub populations (e.g. Black Rocks), this risk should be considered in the <br />context of evidenGe of historic hybridization within the Gila complex that predates human <br />modification of the river system (Dowling and DeMarais 1993). -Hybridization in Gila is in part <br />a natural phenomenon (McElroy and Douglas 1995). Given that some hybridization between <br />bony tail, humpback chub, and roundtail chub in the wild is possible, it may be negligible <br />considering the 1) niche separation among these three species, 2) factors contributing to the . <br />bonytail's decline and disappearance, and 3) available evidence for hybridization. <br /> <br />Vanicek anC Kramer (1969) and Kaeding et al. (1990) suggest ethological mechanisms may <br />separate bonytail spatially from humpback and roundtail chub during spawning based on field <br />collection results. In looking at the apparent niches occupied by the three Gila species in the <br />Upper Basin, round tail chub appear to be largely a tributary stream species, being most abundant <br />in the Yampa, White, upper Colorado, Gunnison, and Dolores rivers; while the humpback chub <br />is largely a deepwater, canyon species found in the Yampa, Westwater, Cataract, Desolation-Gray <br />and Black Rocks canyons (for example). This leaves the mainstem rivers and floodplains as an <br />"available" niche for another Gila species, such as bonytail. As speculation, it is possible the <br />significant loss of 1100dplain habitat with increasing abundance of nonnative fish predators and <br />competitors in remaining floodplain habitat could account for the disappearance of bonytail <br /> <br />10 <br /> <br />r <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 />I <br />I <br />I <br />I <br />I <br />I <br />lJ <br />