Assessment of population substructure in relation to summer feeding ground use in the eastern North Pacific gray whale

Abstract

The eastern North Pacific gray whale Eschrichtius robustus was removed from the US Endangered Species List in 1994, and since then aboriginal groups in Washington (USA) and British Columbia (Canada) have discussed the resumption of traditional whaling. In particular, the Makah are pursuing legal permission to resume their hunt. Although the majority of whales in this popula- tion migrate to summer feeding grounds in the Bering, Chukchi, and Beaufort Seas, a small number of individuals (~200) spend the summers feeding in the waters ranging from northern California to southeast Alaska. The relationship of these 'southern feeding group' whales to the rest of the popu- lation is unknown. This information is key to making appropriate management decisions, because these whales inhabit the waters directly adjacent to the aboriginal communities interested in resum- ing whaling. We compared mitochondrial sequence data from 40 southern feeding group individuals to sequences from 105 individuals representing the larger population. We found significant differ- ences in haplotype frequencies between the 2 groups, with an estimated long-term rate of exchange between the groups being <<1%. Moreover, estimates of Θ (Neµ for mtDNA data, i.e. the probability of a mutation occurring within the population in each generation) were significantly different between the 2 groups, indicating that the maternal lineages of the southern feeding group represent a distinct seasonal subpopulation. Combined, these data show that the southern feeding group of gray whales qualifies as a separate management unit, which should be considered when making con- servation decisions.