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<br />species, may be the cause of the recent genetic pattern of introgression. <br />Alternatively, the Gila genus may represent a natural hybrid swarm (Echelle <br />1984; Wilde and Echelle 1992; Dowling et al. 1995) with levels of <br />introgression continuously changing as a consequence of natural population <br />fluctuations. <br />Although hybridization may be a natural part of the evolutionary history <br />of the Gila complex, a successful reintroduction (as defined by the Recovery <br />Implementation Program) can only occur if, at least, some bonytail can remain <br />isolated until the population is stable. A more natural flow regime, such as <br />spring peaks and late summer low flows, may provide the necessary hydrologic <br />conditions for the successful execution of spatial, temporal or ethological <br />isolating mechanisms. However, this mechanism(s) should be understood to <br />ensure successful reintroduction. <br />Nonnative fish interactions <br />Nonnative fish interactions also impact native fish populations (Kaeding <br />et al. 1986). Successful bonytail reintroduction requires minimizing impacts <br />from nonnative fishes. Unfortunately, these impacts have only been minimally <br />assessed to date. An in-depth understanding of community dynamics would allow <br />a more effective reintroduction effort (Chart and Cranney 1993). <br />One possible way to reduce impacts of nonnative fishes is to reduce <br />their numbers. Minckley and Meffe (1987) found that nonnative fish gradually <br />dominated native fish during low discharges. However, during high flows, <br />native fish were dominant in number. Valdez (1985) noted that numbers of <br />age-0 nonnative fish were highest during low flow years. Floods may prevent <br />successful spawning and recruitment of nonnative fishes, which are usually not <br />adapted to high flows or flooding conditions. <br /> <br />16 <br />FAI