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28 I I I I, I I I I I I I , ,I I ,I I I I I RECOMMENDATIONS Many factors affect the suitability of nursery habitat of age-O Colorado squawfish and hence, their survival. River level and stability, as well as ice processes, are the overriding environmental factors that most affect overwinter backwater pennanence. Backwaters that persist over winter are more likely to enable young squawfish to survive in sheltered, food-rich environments. Attempting to maintaining these backwaters during winter through operations of Flaming Gorge Dam is likely to have only limited success, because the factors that most affect backwater suitability are environmental factors that override the effects of dam operations. While maximum power generation can increase releases from 800 to 4,200 cfs and cause a stage change of about 58 cm at Mitten Park (67 miles below the dam), 45 cm at Jensen Bridge (108 miles below the dam), and 15 cm at Ouray Bridge (162 miles below the dam) (Valdez and Masslich 1989), periodic overwinter flow spikes from tributaries, particularly in early March, can result in much greater stage changes. We believe that these daily fluctuations from hydropower generation destabilize some backwaters and transport fish downstream. However, we also believe that large flow spikes from tributary input, particularly in March and April, serve to disperse large numbers of young Colorado squawfish downstream. We believe that this is a natural phenomenon that is a part of the life cycle of this potomodromous specles. The second factor that overrides the effect of dam operations is air temperature. Although water , released from Flaming Gorge Dam is relatively warm in winter, the river temperature at Jensen (108 miles below the dam) is usually colder than at Green River (290 miles below the dam), primarily because winter air temperatures in the Umta Basin (Jensen area) are often colder than at Green River, UT. Hence, despite relatively warm releases from the dam, the thennal effect is not seen about 100 miles downstream. Because uncontrolled environmental. factors seem_to override the effect of dam operations in winter, recommendations for flow releases from Flaming Gorge Dam cannot be made at this time, without additional information on the relationship between ice processes and dam operations. In the meantime, interim flows should be established to protect, as best as possible, the nursery habitats of age-O Colorado squawfish in the Green River. At the very least, the same principles used to establish summer and fall flows continue to apply to the winter period. Operations that result in alternate desiccation and inundation of backwaters destabilize these nursery habitats and likely decrease survival of the fish from increased exposure to predation and from stress and extra energy expenditure in seeking new habitats. We also hypothesize, but have not yet demonstrated, the phenomenon that frazil ice and jam ice can decrease free water and increase chances of supercooling in backwaters. This phenomenon may occur more eXtensively in more severe winters, but the relationship between flow volume, flow fluctuations, and air and water temperature are not understood for the Green River. We advise caution in making substantial changes to the present operation on the basis of the findings of this study, primarily because our results are based on data from two relatively mild winters.