Large-scale use of parentage assignment of stocked Connecticut River, U.S.A., Atlantic salmon (Salmo salar) fry to determine stocking tributary of emigrating smolts and returning adults requires both parentage assignment and grandparentage assignment. Using computer simulations, we explored the levels of genetic diversity necessary to provide adequate parentage and grandparentage assignment. When matings were known, as in a hatchery, 95% correct grandparentage assignment typically required at least twofold more alleles per locus than did 95% correct parentage assignment. Parentage assignment with unknown matings (as in the wild when parental genotypes can be assayed) required an intermediate number of alleles per locus and grandparentage assignment with unknown matings required the greatest genetic diversity. Computer simulations using empirical parental genotypes (14 loci) and known P1 matings indicated that the genetic diversity of Connecticut River Atlantic salmon broodstock is sufficient to assign all F1 and 97% of F2 offspring to the correct set of two parents or four grandparents, respectively. Grandparentage assignment with unknown P1 matings was ineffective (assignment success = 20%). These results indicate that the combination of parentage and grandparentage assignment can be used as a non-lethal, permanent, heritable "mark" to identify stocking tributary or other management directed characteristics of stocked fry.
