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28 reduces the value of these habitats for endangered fishes. Furthermore. higher flows are required to flush sediments from vegetated backwaters than from unvegetated ones. Qsmundson and Kaeding (1991) reported observations that. on the 15-mile reach during the drought years of 1988 to 1990. backwaters were filling in with silt and spring flows were not sufficient to flush out the fine sediment. Also. they reported that tamarisk colonized sand and cobble bars. The lower frequency of high water years, therefore. decreases the frequency at which silt and sand is flushed from backwaters. fine sediments are flushed from gravel/cobble substrates. and vegetation is scoured from backwaters and bars. As a result. the frequency 'at which these habitats are suitable for use by endangered fishes has decreased. Seasonal Habitat Availability Summer (August-Qctober): Qsmundson et al. (1995) reported that availability of habitats did not differ significantly between periods of moderate flows and low flows. Though absolute area of habitat decreases with declining flows, relative area or percent composition of habitat types changes little. However. squawfish habitat use patterns did change. The fish used a greater variety of habitats during moderate flows than during low flows, During moderate flows. the fish used primarily backwaters, eddies. and pools. During low flows. the fish used slow and fast runs almost exclusively, The change in habitat use without a corresponding change in relative habitat availability indicates that other factors also influence habitat selection. These factors could include changes in quality of physical habitat features such as diversity, depth. dissolved oxygen. etc., or changes in biotic interactions. Qsmundson et al. (1995) interpreted the squawfish behavioral changes as reflective of suboptimal conditions; the behavioral changes demonstrate the ability of the species to modify their habitat use patterns to temporarily cope with adverse conditions and do not demonstrate habitat preferences under optimum conditions. Qsmundson et al. (1995). therefore. based their flow recommendations on the habitat-selection behavior of adult squawfish observed during the higher somewhat more natural flow conditions. Winter (November-March): Qsmundson et al. (1995) reported that flows during the winter are usually moderate because no water is diverted for irrigation and because additional water is released through upstream dams to increase reservoir storage capacity in anticipation of spring runoff. The relative availability of slow runs and riffles during the winter was very similar to their availability during summer. As in the summer. backwaters, eddies, and pools were the preferred types of habitat in the winter. However. whereas eddies were most preferred in summer, pools were most preferred in winter. Adult squawfish used fewer habitat types overall during winter than during