Stock definition and genetic composition of Cumberland Sound beluga whales (Delphinapterus leucas)

Abstract

Less than 1,500 beluga whales (Delphinapterus leucas) are estimated to be in Cumberland Sound. These whales, considered as a single population of beluga, have been listed as Threatened under the Species at Risk Act and recently assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada. This beluga whale group has been defined based on satellite tracking data, contaminants, morphometrics, and previous genetic analyses. However, questions regarding whether multiple populations of beluga whales visit Cumberland Sound, their genetic stock discrimination, and the timing of migration and distribution of whales from different groups within Cumberland Sound remain. A recent reexamination of a long haplotype of the mitochondrial DNA (mtDNA) control region showed greater discrimination among beluga whale populations in Eastern Canada, including a small subsample of whales harvested from Cumberland Sound. In this study, we reexamined the genetic distinctiveness of beluga whales hunted in Cumberland Sound (N = 208) compared with other Eastern Arctic whales (N = 657), analyzing all samples collected from this area with the long haplotype of mtDNA. We also genotyped a subsample of whales harvested in Cumberland Sound (N = 27) and Western Hudson Bay (N = 121) using 12,370 nuclear DNA (nDNA) single nucleotide polymorphisms (SNPs) to investigate their distinctiveness. Our results using mtDNA confirmed that approximately 35% of beluga whales harvested in July and August from Cumberland Sound had haplotypes private to this region. The rest of the harvested whales had haplotypes shared with other populations from the Hudson Bay-Strait Complex. Nuclear DNA results also suggested the presence of two populations in Cumberland Sound during summer with approximately 74% of the whales belonging to the CSB population. The degree of differentiation between the CSB and WHB populations was low (FST=0.014), but this is expected given the recent colonization of the Hudson Bay-Strait Complex. Our results support that there are two populations of beluga whales that summer in Cumberland Sound. Based on all current information, managing beluga whales inhabiting Cumberland Sound in the summer as a single stock comprised of two genetic populations is the most precautionary approach.