High Genetic Heterogeneity in Chum Salmon in Western Alaska, the Contact Zone between Northern and Southern Lineages

Genetic relationships among 64 spawning populations of chum salmon Oncorhynchus keta in western Alaska were studied using allele frequency data from 40 protein‐encoding loci. Two major lineages of chum salmon inhabiting Alaska were detected using clustering and multidimensional scaling analyses of Cavalli‐Sforza and Edwards' chord distances. Populations of the northwest Alaska lineage occur in the largely unglaciated areas of Alaska north of the Alaska Peninsula (Beringia, the Beringian Refugium), and the Alaska Peninsula–Gulf of Alaska lineage occurs in the glaciated and unglaciated areas of the Alaska Peninsula, Kodiak Island, and southcentral Alaska. The two lineages come into contact in the 150‐km area separating Herendeen Bay and Port Heiden on the northern Alaska Peninsula; this area may represent a major zoogeographic contact zone. Genetic data also suggest the lineages come in contact in upper Cook Inlet; the population representing the Susitna River drainage, which drains into Cook Inlet and the Gulf of Alaska, shows affinity to the northwest Alaska lineage. Genetic variability was higher in the Alaska Peninsula–Gulf of Alaska lineage than in the northwest Alaska lineage. A comparison of allele frequency data collected in this study with data available for Pacific Rim populations suggests that populations of the Alaska Peninsula–Gulf of Alaska lineage were derived from Cascadia (the Pacific Refugium) and belong to a larger southern lineage, which includes populations from southeast Alaska, British Columbia, and the Pacific Northwest. In contrast, populations from northwest Alaska appear to be derived from a northern lineage with affinities to Asian populations.