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1 <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br />ii <br />1 <br /> <br /> <br /> <br /> <br />temperatures may not accurately portray temperature preferences of Colorado <br />squawfish because the species frequently utilized habitats outside the main <br />river channel, such as large backwaters, gravel pits, and flooded bottomlands, <br />which may be controlled more by ambient air temperatures and solar radiation. <br />In laboratory experimentation, Marsh (1985) found that optimal temperatures <br />for embryo development and hatching of Colorado squawfish was near 200C <br />(68oF). Percentage hatch was highest and incidence of abnormalities lowest at <br />that temperature. Tyus (1991) found that young Colorado squawfish moved in <br />and out of backwater habitats as water temperatures fluctuated. The young <br />fish apparently moved into backwaters that were warmer that the river <br />channels, but moved back into the river as backwater temperatures declined. <br />Temperature preferences have been determined in the laboratory .for Colorado <br />squawfish reared at Willow Beach National Fish Hatchery in Arizona. Juvenile <br />Colorado squawfish acclimated to 200C (68oF) selected a higher temperature <br />(26.60C [800F]) than those acclimated to either 26oC (78oF) or 140C (570F); <br />fish acclimated at 26oC (78oF) selected 23.70C (750F); and those acclimated at <br />140C (570F) selected 21.90C (710F). Adults selected temperatures ranging from <br />21.50 (710F) to 25.70C (78oF), with a final temperature preference of 25.40C <br />(78oF) (Bulkley et al. 1982). Maximum growth of 45 to 100 mm (1.7-4 in.) TL <br />Colorado squawfish in a laboratory study occurred at 250C (770F), while growth <br />at 200C (68oF) and 300C (860F) was about 50 percent of the maximum (Black and <br />Bulkley 1985). <br />Table 1. Temperatures associated with Colorado squawfish migration and <br />spawning periods in the Yampa River, 1981-88 [adapted from Tyus and Karp <br />(1989)]. <br />Type <br />Water Migration Spawning_ <br />Year Year Period Temp.(mean) Period Temp.(median) <br />Dates C0 F~ Dates C0 F° <br />1981 Low 5-12 to 6 -20 13. 80 570 6 -19 to 7-20 21.. 80 710 <br />1982 Average 6-10 to 6- 20 12. 70 550 7 -4 to 8-8 22. 00 720 <br />1983 High 6-10 to 7-10 13.40 560 7-12 to 8-18 22. 50 730 <br />1984 High -- -- 7-10 to 8-17 22. 00 720 <br />1985 High -- -- 6-21 to 7-25 20. 00 680 <br />1986 High -- -- 6-27 to 8-5 20. 80 690 <br />1987 Low -- -- 6-3 to 7 -16 20. 50 690 <br />1988 Average 6-8 to 6-30 16.90 620 6-20 to 7-24 21. 50 710 <br />7 <br /> <br />