Robin S . Waples David J . Teel Genetic isolation of previously indistinguishable chinook salmon populations of the Snake and Klamath Rivers : Limitations of negative data

Northwest Fisheries Science Center. National Marine Fisheries Service. NOAA 2725 MontJake Boulevard East, Seattle. Washington 98 J 12 Fred M. Utter Robin S. Waples David J. Teel Genetic isolation of previously indistinguishable chinook salmon populations of the Snake and Klamath Rivers: Limitations of negative data Abstract.-An anomalous inability to distinguish certain geographically-separated chinook salmon Oncorkynckus tskaWlJtsCka. populations of the Snake River and the Klamath River from a survey of 18 polymorphic loci led to a prediction that distinction would ultimately be found through sampling of additional polymorphic loci. Recently published studies involving pertinent groups within each of these rivers included data from an additional 15 polymorphic loci, and therefore allow a reexamination of the relationships between these groups. Comparison of results for the new studies shows the formerly indistinguishable groups from two areas to be as distinct from one another as from other major groupings of the species with a mean genetic distance between populations of each river (0.014) that is double that of the maximum withingroup genetic distance. Two newlyresolved gene loci (rnMDH-2" and sMEP-1"') are particularly good at distinguishing populations from the two rivers. In addition to resolving the anomalous similarity between populations inhabiting geographically separated areas, the new results illustrate the care that must be used in drawing inferences from negative data.