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<br />3 <br /> <br />were made from 1977-1979, and Vanicek's (1967) data from Dinosaur <br />National Monument, collected in 1964-1966. These data represent the <br />results of the only studies where information on reproductive success <br />is available for at least a 5-year period. Information from other <br />short-term studies are included to support or reject the conclusions <br />drawn from these two base studies. Figure 1 is a map of the upper <br />Green River system showing localities mentioned in the text. <br />Vanicek (1967) showed that young squawfish could be aged quite <br />readily by length/frequency analysis, especially for the first 3 years <br />of life. Older fish were more difficult to age. Therefore, this <br />study concentrated on the first 3 or 4 age groups, young-of-the-year <br />(age group 0), yearlings (age group I), two year olds (age group II), <br />etc. Squawfish usually spawn in July or early August in the upper <br />Green River (Vanicek and Kramer 1969; Holden and Stalnaker 1975), <br />therefore Age 0 fish are found in August-December of a given year, <br />Age I during the next year, and so on. Successful reproduction in an <br />area was determined by the number of young squawfish caught where <br />sufficient effort was expended to ascertain their presence. Sufficient <br />effort was defined as sufficient seine hauls in the habitats most <br />likely to produce young squawfish. Young-of-the-year squawfish are <br />readily caught with seines in Au~ust, September, and October. <br />Yearling squawfish are most readily cau9ht in May and June but are found <br />throughout the year, as are age II fish. Age II fish are caught less <br />frequently than either ages 0 or I, which is as expected due to juve- <br />nile mortality and perhaps changes in preferred habitat. This approach, <br />