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Executive Summary <br />The humpback chub (Gila cypha) is an endangered species native to the Colorado <br />River Basin listed under the Endangered Species Act in 1967 (32 FR 4001). The <br />"Yampa" population of humpback chub includes individuals that may be found in <br />Yampa, Lodore, Whirlpool, and Split Mountain canyons and is one of the smallest <br />existing populations of humpback chub (USFWS 2002). The objectives of this .study are <br />to define the distribution, length frequency and abundance of the adult Yampa humpback <br />chub population and numbers of juveniles in the Yampa humpback chub population. <br />A two-year study began in 2003 that sampled adult humpback chub using <br />trammel nets, boat electrofishing and angling. Juvenile fish were collected using <br />backpack electrofishing and seining. All adult humpback chub were measured for total <br />length (TL), weighed, scanned for the presence of passive integrated transponder (PIT) <br />tags, tagged with PIT tags if none were found and immediately released. All juvenile <br />samples were preserved for laboratory identification. <br />During the two-year study, 13 adult humpback chub were captured (10 in Yampa <br />Canyon and 3 in Whirlpool Canyon) and three hundred and forty nine juvenile Gila spp. <br />were collected of which 30 were questionably identified as G. cypha. Abundance <br />estimates were not possible due to the low number of captures. Distribution was similar <br />to historical ranges. Catch per effort of adult humpback chub dramatically decreased <br />from other recently collected data. <br />vi <br />