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ABSTRACT <br />Gila cypha (the humpback chub) is a unique but endangered <br />cyprind fish endemic to the Colorado River system in western <br />North America. Its distribution within the system is patchy; <br />occurrence is restricted primarily to narrow, canyon-bound <br />reaches of these rivers. Greatest abundance is achieved at the <br />confluence of the Colorado and Little Colorado rivers (= LCR) in <br />northern Grand Canyon (Coconino Co., AZ). This study defines the <br />nature and extent of G. cypha's movements within the LCR, and <br />tests the hypothesis that its duration of stay within that river <br />is restricted to the reproductive period. <br />During 1991/92, adult G. cypha were captured and tagged <br />during 19 6--14 day sampling periods in three separate reaches of <br />the LCR. From these data, population estimates were derived for <br />each reach on a monthly basis, by month for the entire LCR, and <br />over the entire study period. Results indicate an upriver <br />migration by some individuals in early spring, followed by a <br />slow, protracted post-reproductive movement downstream. <br />Localized stasis by adults in the LCR, particularly summer <br />through winter, is also strongly supported by the data. <br />Movements by G. cypha in the LCR thus appears to be an amalgam of <br />two processes: Upriver movement in spring coupled with localized <br />movements by overwintering adults. The latter suggests a possible <br />alteration in life-history strategy for the species, and is <br />discussed in the context of Glen Canyon Dam, built in 1963 to <br />impound Lake Powell at the northern extent of Grand Canyon. <br />7