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<br />1992). An analysis of larval humpback chub collections and habitat is the subject of ongoing <br />GCES research being conducted by the AGFD. <br /> <br />Y oung-of-year humpback chubs, including .larvae, use backwaters, eddies, and .runs (reviewed <br />by Miller and Hubert 1990). Holden (1977) sampled those habitats in Desolation Canyon and <br />Gray Canyon on Green River in, proportion to their, occurrence. and. reported- young-of-year <br />humpback chubs (30 to 70 mm total length) preferred backwaters with no current, a firm silt <br />bottom, and 0.6 m m~imum depth. Deeper eddies and slow runs also received some use. <br />Kaeding and Zimmerman (1982) commonly collected young-of-year and juvenile life stages from' <br />shoreline/run and shoreline/eddy LCR habitats. Valdez (1990) collected larvae and young-of- <br />year .humpback chubs from backwaters (most occurrences), .along shorelines, and in isolated <br />pools in Cataract Canyon on the Colorado River. Valdez et al. (1990), using 'humpback chub <br />data from the Green River (1500 observations), found larvae (<21 mm) at.a mean depth of 0.4 <br />m (range 0.03 to 2.5 m) and in water velocities less than 0.03 mls (range <0.0 to 0.09 m/s). <br />Young-of-year were found in mean water depths of 0.6 m and mean velocities 0.06 m/s. <br /> <br />Juvenile humpback chub are frequently found in eddy habitats and also in other low to moderate <br />velocity areas (Kaeding and Zimmerman 1982; Tyus and Karp 1989). Valdez et al. (1992a) <br />captured juvenile humpback chub along Grand Canyon main stem shoreline habitats with talus <br />slopes, earthen banks with root wads, and near large standing boulders. Pockets of sand were <br />prevalent in those habitats, but few juvenile humpback chubs were captured on sand beaches. <br />Including data from upper basin studies, Valdez et al. (1992a) report for humpback chub a.... <br />transition in habitat use with size or age from shallow, protected areas such as backwaters or <br />stable shorelines to areas with moderate depth and velocity and uneven substrate. . <br /> <br />Critical Habitat <br /> <br />Critical habitat is defined in the Endangered Species Act to include areas, occupied or not, that <br />are essential to the conservation of the species. Conservation is defined as that needed to bring <br />about the complete recovery of the species. Thus, critical habitat preserves options for a <br />species' eventual recovery. Of the 610 km of critical habitat designated for the humpback chub <br />in the Colorado River basin, 291 km are found in the project area (U.'S. Fish and Wildlife <br />Service 1994a). This includes the lower 13 km of the LCR and from Natuloid Canyon (about <br />RM 34) to Granite Park (about RM 208) on the Colorado River. <br /> <br />In determining which areas to designate as critical habitat, the Service considers those physical <br />and biological attributes (constituent elements) that are essential to species conservation. Known <br />constituent elements for the Colorado River endangered fishes include water, physical habitat, <br />and biological environment as required. for each. particular life. stage; These primary elements <br />include, but are not limited to the following: <br /> <br />Water" This includes. a quantity of water of sufficient. quality (Le., temperature, <br />dissolved oxygen, lack of .contaminants, nutrients, and turbidity) that is delivered to a <br />, specific location in accordance with a hydrologic regime that is required for the particular <br />life stage for each species. <br /> <br />IS December 1994 final biological opinion 2-21-93-F-167 <br /> <br />11 <br /> <br />I <br /> <br />~ <br /> <br />,-". <br /> <br />'.' <br /> <br />'-'.; <br /> <br />:,;,' <br /> <br />~- <br />;~ <br />"-' <br /> <br />., <br /> <br />,". <br /> <br />;.. <br /> <br />',' <br /> <br />:,'~~ <br /> <br />r": <br /> <br />"'! <br /> <br />~, <br /> <br />(1: <br />';1{; <br />1;;:; <br />~I.' <br />~,~~ <br /> <br />,-;" <br /><<'.: <br />