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breeding population size, it might be genetically harmful because of an overall drop in Ne, and elevated rates of inbreeding and genetic drift (Waples and Do 1994, Wang and Ryman 2001). The end result is that supported populations can end up being more at risk to extinction then they would have been with no captive propagation and supplementation activities. Some guidelines for avoiding reductions of Ne are given in Tringali and Bert (1998). For example, in wild populations with an initial Ne greater than 500, a relative hatchery contribution of less than 17% should not drive the total Ne to or below 500, provided a sufficient number of hatchery breeders are used (> 50). However, even using 100 effective hatchery breeders, and regardless of the original wild Ne, hatchery contributions larger than -45% will result in values of Ne below 500. This implies that hatchery supplementation should be a very slow and protracted operation in order to minimize risk. Because of their small numbers, and relaxation of wild selective forces, captive bred individuals can undergo domestication, a process of rapid and significant evolutionary change in morphological, behavioral, and physiological traits that compromise fitness in a natural setting (Kohane and Parsons 1988, Arnold 1995, Frankham and Loebel 1992, Ruzzante and Doyle 1993). Captive populations can rapidly accumulate deleterious alleles (i.e., they can rapidly accumulate behavioral or morphological traits that are conducive to living in a hatchery situation, but are deleterious in the wild; Lynch and O'Hely 2001). With sufficient gene flow of deleterious alleles from the captive population, the wild population can become transformed into a genetic state such that complete collapse can occur in the absence of continued supplementation (Lynch and O'Hely 2001). This problem increases over time, because serious depletion of heterozygosity is more likely when a population is supported for multiple generations by hatchery-raised fish (Ryman and Laikre 1991). Sometimes, these problems are addressed by continually introducing wild individuals into the captive stock (Utter 1998). However, Ford (2002) found that substantial phenotypic changes and fitness reductions can occur even if a large fraction of the captive broodstock is brought in from the wild every generation. He suggests that regularly bringing in wild-origin brood stock into captive populations cannot be relied upon to eliminate the effects of inadvertent domestication, although the rate will be reduced compared to a completely closed captive population. Ford (2002) also pointed out that attempting to minimize selection for domesticated traits in captivity can help alleviate the problem; however, the wild population is not protected from a decline in fitness unless gene flow from the captive population approaches zero. This means that the very populations in need of supplementation (such as endangered species with low population abundances) can easily become the most susceptible to the deleterious effects of gene flow from captive propagation (i.e., the fraction of surviving captive offspring entering the wild population becomes larger, together with the increasing associated risks). 14