Stock structure issues related to western gray whales
John W. Bickham, Anna Bruniche-Olsen and J. Andrew DeWoody
International Whaling Commission
Abstract: This paper focuses on issues of population structure of North Pacific gray whales (Eschrichtius robustus) as they relate to status, conservation and management. Specifically, we review and summarize recent genetics and genomics studies that provide new insights on population structure and evolutionary history gray whales. We conclude that the whales summering near Sakhalin Island are descended from eastern gray whales because: 1) they do not show distinct mtDNA lineages and only show low levels of differentiation at mtDNA haplotype frequencies, SNP frequencies and microsatellite frequencies. These are all expected results of a recent founder event. 2) It would explain why these animals travel from Sakhalin to Mexico, a trip of considerably greater distance, and energetic cost, than from Sakhalin to the presumed Asian wintering grounds in the South China Sea. And 3) we see no evidence in the genetics and genomics results that suggest there is a distinct western breeding stock. Cooke et al., (2019) estimates that this comprises approximately 45% of the Sakhalin population. We would expect this group to be distinct from the eastern genotype and western genotype animals, since we know members of both these groups travel to Mexico. No evidence of a third genotype group was found in the Lea or STRUCTURE analyses reported by Brüniche-Olsen et al. (2018a).