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<br />~.DCb I (Dj~\ ^~e:l u...\ <br /> <br />Nonh American Journal of FisMries Managemen! 26:233-245, 2006 <br />@ Copyrighl by lite American Fisheries Socie1y 2006 <br />DOllO.1577/MOS-07S.1 <br /> <br />17;4 <br /> <br />[Article] <br /> <br />Abundance Trends and Status of the Little Colorado River <br />Population of Humpback Chub <br /> <br />LEWIS G. COGGINS JR.* <br /> <br />u.s. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research <br />Center, 2255 North Gemini Drive, Flagstaff, Arizona 86001, USA <br /> <br />WILLIAM E. PINE III <br /> <br />Department of Fisheries and Aquatic Sciences, University of Florida, 7922 Northwest 71st Street, <br />Gainesville, Florida 32653, USA <br /> <br />CARL J. WALTERS <br /> <br />Fisheries Centre, University of British Columbia, 2259 Lower Mall, <br />Vancouver, British Columbia V6T 1ZA, Canada <br /> <br />DAVID R. VAN HAVERBEKE <br /> <br />U.S. Fish and Wildlife Service, Arizona Fishery Resources Office, <br />323 North Leroux, Suite 401, Flagstaff, Arizona 86001, USA <br /> <br />DA VID WARD <br /> <br />Arizona Game and Fish Department, Research Branch, <br />2221 West Greenway Road, Phoenix, Ariwna 85023, USA <br /> <br />HELENE C. JOHNSTONE <br /> <br />SWCA Environmental Consultants. <br />114 North San Francisco Street, Suite 100. Flagstaff, Arizona 86001, USA <br /> <br />Abstract.- The abundance of the Little Colorado River population of federally listed humpback chub Gila <br />cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture- <br />recapture-based abundance estimators. Analyses of data from all sources using various methods are consistent <br />and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high <br />proportion (> 80%) of the adult population being marked by the mid-I 990s. Analysis of these data using both <br />closed and open abundance estimation models yields results that agree with catch rate indices about the extent <br />of the decline. Survival rates for age-2 and older fish are age dependent but apparently not time dependent <br />Back-calculation of recruitment using the apparent 1990s population age structure implies periods of higher <br />recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and <br />Wildlife Service recovery criterion of stable abundance is not being met for this population. Also, there is <br />a critical need to develop new abundance indexing and tagging methods so that early, reliable, and rapid <br />estimates of humpback chub recruitment can be obtained to evaluate population responses to management <br />actions designed to facilitate the restoration of Colorado River native fish communities. <br /> <br />The humpback chub Gila cypha, a cyprinid endemic <br />to the Colorado River basin, was described in 1945 <br />from a specimen captured near the mouth of Bright <br />Angel Creek in Grand Canyon, Arizona (Miller 1946). <br />This morphologically unique cyprinid has been <br />characterized as the most specialized member of the <br />genus Gila and is highly adapted to exist in turbulent <br />canyon-bound reaches of the Colorado River basin <br />(Minckley 1973). This species was included on the <br /> <br />* Corresponding author: IcogginS@usgs.gov <br /> <br />Received May 6, 2005; accepted August 15, 2005 <br />Published online February 3, 2006 <br /> <br />federal list of endangered species in 1967 (USOFR <br />1967) and is protected under the Endangered Species <br />Act (ESA) of 1973. Presently, only six populations are <br />known, five in the upper basin of the Colorado River <br />(i.e., above Lees Ferry) and one in Grand Canyon <br />(Valdez and Ryel 1995). <br />The humpback chub population in Grand Canyon is <br />centered near the confluence of the Colorado and Little <br />Colorado rivers (LCR) in Grand Canyon (36. 19"N, <br />111.79"W; Kaeding and Zimmerman 1983; Douglas <br />and Marsh 1996; Gorman and Stone 1999). Valdez and <br />Ryel (1995) describe the humpback chub distribution <br />as consisting of nine aggregations throughout Marble <br /> <br />233 <br />