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sample, it does not provide an accurate indicator of change in the genetic composition of hatchery stocks relative to natural populations (see Allendorf and Ryman [1987, p. 147] for a similar conclusion relative to allozyme diversity). In a second set of simulations where progeny were derived from broodstocks of different size, mean h values for progeny populations increased rapidly with increased founder size, producing a curve which leveled at h = 0.95 and broodstock sizes near 20 individuals (Figure 5). Therefore, in an organism with high diversity (i.e., each individual possessing an unique haplotype), this measure of genotypic diversity misrepresents levels of variation maintained in the broodstock, e.g., the difference in diversity values from stocks generated by random use of ova from 15-20 females will not be significantly lower than those produced from 100 females, even though the progeny of 100 females will clearly possess more different genotypes than those produced from 15-20. Simulation results are consistent with our empirical data. Yeaz classes in 19$7 and 1989 exhibited similar diversity values despite substantial differences in the number of females used to generate each (Table 4). Thus, variation in diversity was not due to the number of females used (17 in 1990 versus 55 and 14 for the 1987 and 1989 yeaz classes, respectively). Given the relative insensitivity of h to broodstock size, reduced diversity in the 1990 year class clearly indicates the difficulty in consistently producing stocks mimicking a source population. Factors reducing diversity in hatchery stocks.- Reduction in diversity could be due to extrinsic (i.e., hatchery effects) and/or intrinsic (differences in fecundity/viability among females and their progeny) factors. We cannot assess the role of extrinsic factors. They should be consistent, however, since in this example, personnel, methods, and equipment at DNFH were relatively constant year to year. 20