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monitored radiotagged adult Colorado squawfish and razorback suckers moving from the path of <br />flowing ice jams at Rainbow Park and Island Park. <br />Valdez and Masslich (1989) also observed that frazil ice in the Colorado squawfish nursery <br />area of the Green River near Jensen could exclude young fish from backwaters, causing greater <br />energy expenditure and exposure to predation. Frazil ice in the area in Winter 2 was up to 3 m thick <br />and stacked onto shallow shorelines and in backwaters. Tyus and Karp (1990) reported that <br />fluctuating flows in 1987-88 caused flooding and dewatering of low-lying areas at Ouray due to ice <br />jams. Lower, more stable flows in 1988-89 resulted in shallower backwaters but less shoreline <br />scouring. Few young Colorado squawfish were captured with baited minnow traps in backwaters, and <br />the effect of ice conditions on this species was inconclusive. <br />Adult Colorado squawfish in the Yampa River used low velocity habitats that were the first <br />to develop surface ice. Surface ice formed on these areas as early as November 11, 1986 and <br />November 17, 1987. The fish used these ice-covered habitats, when the swifter main channel <br />remained ice-free. Because lower velocity areas were the first to freeze, ice served as a velocity <br />indicator. Adult Colorado squawfish were apparently attracted to these ice-covered habitats for low <br />velocity, cover, security, and food. Large schools of small fish were observed through the thin ice <br />near shore that could provide available forage for this large piscivore. <br />Wick and Hawkins (1989) hypothesized that the initial attraction by Colorado squawfish to <br />ice-covered habitats was for security and cover from avian predators, while allowing the 6sh to forage <br />in shallow water. Valdez and Masslich (1989) reported one radiotagged Colorado squawfish lost to <br />eagle predation on the Green River at Rainbow Park, lending support to the hypothesis of avian <br />predation. Wick and Hawkins (1989) also stated that ice insulates the water, maintaining above- <br />freezing temperatures, high dissolved oxygen, and primary production, while preventing frazil ice <br />formation. They recorded 17 mg/1 dissolved oxygen in an embayment when saturation was 12 mg/l, <br />indicating ongoing primary production and photosynthesis. Maintenance of these nutrient-rich <br />embayments and backwaters could be critical to overall productivity of the ecosystem in winter. <br />31 <br />