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<br />3 <br />The Colorado squawfish has historically been the top predator in the <br />Colorado River Basin (Glick et al 1983). Alterations and modifications to the <br />Colorado River system has caused the Colorado squawfish to become reduced in <br />numbers and range (Seethaler 1978). Presently listed as an endangered species, <br />the Colorado squawfish occupies the few- remaining,free flowing sections of this <br />river system (Behnke and Benson 1983). <br />The life history and biology of Colorado squawfish has been well doc- <br />umented (Vanicek 1967, Seethaler 1978, Holden and Glick 1981, Miller et al <br />1982). Extensive field and laboratory studies dealing with this fish have <br />been conducted by state and federal agencies. Much of the data that has been <br />collected by agency personnel has not been sufficiently analyzed. These data <br />could prove important to the future understanding of the Colorado squawfish <br />and aid in ensuring its survival in the upper Colorado River system. <br />The purpose of this study was to determine the age and growth of Colorado <br />sauawfish within the Yampa River. The objectives of this study were as follows. <br />1) Establish feasibility of determining age of Colorado squawfish by <br />analyzing fish scale structures. <br />2) Determine age structure of Colorado squawfish, <br />3) Compare age structures of Colorado squawfish populations between <br />rivers and years. <br />4) Determine dominant year classes and hypothesize why these years were <br />dominant by comparing Yampa River flow and temperature data. <br />5) Compare growth rates of fish captured in the Yampa River and fish <br />captured in the Colorado River. <br />