Population structure of North Pacific gray whales in light of trans-Pacific movements
A.R. Lang, D.W. Weller, A. M. Burdin, K. Robertson, O. Sychenko, J. Urban R, S. Martinez-Aguilar, V.L. Pease, R. G. LeDuc, D. I. Litovka, V. N. Burkanov, R.L. Brownell Jr.
International Whaling Commission
Although gray whales (Eschrichtius robustus) in the western North Pacific (WNP) were almost extirpated by commercial whaling, catches off Korea in the 1960s and the discovery of whales feeding off Sakhalin Island (SI), Russia, in the 1980s suggested that a small relict WNP population survived. More recent findings that some SI whales overwinter in the eastern North Pacific (ENP), however, have raised the possibility that the persistence of gray whales off SI may partially be driven by the recovery of the ENP population. To better understand the origin of the SI whales, we generated mitochondrial DNA (mtDNA) sequences and microsatellite genotypes (n=12 loci) from 156 whales sampled off SI and compared it to available data from 105 ENP whales. Mitochondrial and nuclear genetic differentiation was found between the SI and ENP whales, and clustering analysis identified two distinct groups among the SI whales, one of which was genetically similar to ENP whales. Both groups contained whales known to migrate to the ENP, and some admixture between them was indicated. Collectively, these findings suggest that the genetic differentiation observed between the SI and ENP whales may be due to selective breeding of SI whales while west of the migratory route used by the majority of ENP whales. The rare but continued reports of gray whales off the coasts of Japan and China, however, confirm that some gray whales overwinter in the WNP. Thus, while our results, reveal that high internal recruitment and a lack of random mating support continued recognition of SI Whales as a demographically independent population, they also highlight the importance of obtaining genetic and photographic data from the whales recorded off Japan and China in order to more fully understand the population structure of gray whales in the North Pacific.