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for choice of hatchery facilities and hatchery operations (e.g., risks of introgression occurring if other Gila spp. are on station or in the watershed). Second, there is risk of inbreeding occurring within the hatchery population. Traits that frequently exhibit inbreeding depression are quantitative, and are associated with reproductive capacityand physiological efficiency (Kincaid 1983, Lande 1981). In order to maintain variability in hatchery populations, a total of 50 to 500 genetically effective founding breeders has been recommended (Franklin 1980, Hynes et al. 1981, Kincaid 1983). However, more recent genetics theory suggests these numbers may be at least an order of magnitude too low for preserving quantitative variability (Lande 1995). The danger is that if hatchery fish are deficient in overall genetic variability, this may decrease genetic variability in the population into which they are released. Lande and Barrowclough (1987) point out that once quantitative variability is lost, a population must regain and sustain high abundance for hundreds to thousands of generations until that variability is replaced by new mutations. The above studies imply that 1) in order to fully retain genetic variability in a captive broodstock, several thousand individuals may be needed, and 2) if quantitative variability is reduced in the wild because of inappropriate hatchery actions, the loss is very long term (Le., an irrevocable mistake can be made). Third, genetic hazard can be imposed upon wild populations via the release of broodstock individuals, resulting in a reduction in effective population size (Ryman and Laikre 1991, Waples and Do 1994, Ryman et al. 1995, Wang and Ryman 2001). Since captive bred populations are usually created using only a very small proportion of the wild population, the captive portion of the population has a low genetic effective population size (Ne). The danger comes from a large portion of the captive bred offspring breeding upon release with the wild population (Ryman and Laikre 1991, Lynch and O'Hely 2001). Hence, the overall Ne (and genetic fitness) of the wild population can be reduced to levels dramatically lower than it would have been with no captive propagation and supplemental stocking (Ryman and Laikre 1991, Waples and Do 1994, Ryman et al. 1995, Wang and Ryman 2001). A low Ne in the wild becomes an accurate predictor of extinction, because of linked mechanisms of reduced gene flow, genetic drift, reduced within population variability, and inbreeding depression (Lacey 1987, Lynch et al. 1995). Because of this effect, genetic variation in supported populations may be at risk, even when presumably adequate numbers of breeders are used. This risk is especially high for fishes, that have high and variable reproductive rates. Furthermore, this risk appears to be contributing to the demise of fisheries on a worldwide basis (Tringali and Bert 1998). If the underlying problems for population decline are not initially addressed (e.g., habitat destruction; Meffe 1992), supported populations may exceed carrying capacity and can then be subject to a "supplementation and crash" scenario (Waples and Do 1994). The supplemented population can then become susceptible to the combined effects of a reduction in Ne, swamping of wild-population alleles by those from hatchery fish, and future drift-associated changes caused by the population crash (Tringali and Bert 1998). If supportive breeding does not result in substantial and continuous increase.of the 13