2004-06-29_PERMIT FILE - C1981038 (3)

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]s reduces existing channel habitat complexity by causing channelization of the river. Dikes and levees also isolate existine floodplain depressions from the channel durins hish flows. The slowed creation of complex channel habitats and new floodplain depressions, the reduction of existing channel habitat complexity, and the isolation of existing floodplain depressions have acted to reduce the quantity and quality of important habitat for endangered fishes. Habitat Maintenance Backwaters, used by ~•arious life stages of endangered fish, are damaged by the deposition of fine sediments which reduces their depth and consequently their duration and frequency of inundation. Gravel and cobble substrates, used by pikeminnow for spawning, aze damaged by the infiltration of fine sediments. The establishment of vegetation on backwater sediments and on bazs fitrther reduces the value of these habitats for endangered fishes. Furthermore, higher flows aze required to flush sediments from vegetated backwaters than from unvegetated ones. Osmundson and ICaeding (1991) reported observations that, on the 15-mile reach during the drought yeazs 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 yeazs, therefore, decreases the frequency at which silt and sand is flushed from backwaters, fine sediments are flushed from graveUcobble . substrates, and vegetation is scoured from backwaters and bars. As a result, the frequency at which these habitats aze suitable for use by endangered fishes has decreased. Seasonal Habitat Availability Summer (August-October): Osmundson et al. (1995) reported that, in the 15-mile reach, availability of habitats did not differ significantly between periods of moderate flows and low flows. Though absolute azea of habitat decreases with declining flows, relative area or percent composition of habitat types changes little. However, pikeminnow habitat use patterns did change. The fish used a greater variety of habitats doting 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. Osmundson et al. (1995) interpreted the pikeminnow 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. Winter (November-Mazch): Osmundson et al. (1995) reported that, in the 15-mile reach, flows during the winter aze 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