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46 <br />• All four rare fishes. <br />o Channel adjustments associated with flow regulation by large dams seem to <br />lead to habitat less suitable to native fishes than were historic flow regimes. <br />Miller et al. (1982c) hypothesized that channel adjustments common to <br />reaches with flow depletions or flow regulation (such as aggradation, <br />channel braiding, covering of gravel and cobble with sand, decreased <br />frequency of overbank flows, and decreased area of deep runs) tend to <br />lead to a channel that is wider, shallower, and warmer than previously. <br />o Fishes trapped in declining backwaters are subject to increased predation by <br />mammals and birds as well as by other fishes. <br />Tyus and Karp (1989) reported a high level of predation on fishes <br />S trapped in declining backwaters. Terrestrial predators were the major <br />threat in many cases. <br />o Native species may be better able than exotic species to escape backwaters <br />before they are isolated from the river channel. <br />Carter et al. (1986) hypothesized that results of Valdez et al. (1982) <br />showing introduced species to make up an inordinate part of fishes <br />captured in declining backwaters to be due to the high level to which <br />native species have adapted to a highly fluctuating flow regime. Native <br />species were getting out of pools before they were cut off from the main <br />C?