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Y = - 26.64 + 2.78 TL (for 22 < TL < 47 mm) <br />Equations were derived from hatchery-reared progeny of parents collected <br />from the upper Colorado River basin. (Hamman 1981). Colorado squawfish fry <br />were raised at Willow Beach National Fish Hatchery (Arizona) for 107 d at <br />temperatures of 21 to 26°C. We reported annual hatching dates as means and <br />as ranges that included 90% of fish hatching dates each year (i.e., dates <br />read from a cumulative frequency distribution at 5% and 95%). Age-0 fish <br />captured above Gray Canyon (RK 256) were judged to have hatched in the <br />upper Yampa River and fish captured below RK 256 presumably hatched in the <br />Yampa and lower Green River. Hatching dates of larval Colorado squawfish <br />were compared with streamflows using U.S. Geological Survey water <br />resources data from the Deerlodge, Colorado, and Green River, Utah gaging <br />stations (Figure 1). <br />An evaluation of relative overwinter survival of age-1 fish was <br />calculated by dividing the seine catch (fish/100 m2) of age-1 Colorado <br />squawfish in river reaches sampled in the spring by catch of the same <br />cohort in those reaches the previous autumn. In each evaluation, the upper <br />Green River (strata E and F) were evaluated separately from the lower <br />(strata A and B), so that two comparisons were made for each year. <br />Differences in mean TL of Colorado squawfish between lower and upper <br />nursery areas and between autumn and spring samples were tested with <br />independent t-tests, assuming unequal variances. Standard regression <br />techniques were used to determine the relationships between size (TL) and <br />late summer (August and September) streamflow and loge (catch-per-unit- <br />effort) and late summer streamflow. Independent t-tests and G-tests of <br />independence (Sokal and Rohlf 1981) were used to evaluate the <br />7 <br />