Comments: Boskovic et al. (1996) examined mtDNA variation among seals from the Gulf of St. Lawrence, Sable Island, Nova Scotia, Norway, and the Baltic Sea. They found no shared haplotypes between the western Atlantic group and the eastern Atlantic group. MtDNA data indicated little or no geogrpahic separation between animals breeding in the Gulf of St. Lawrence and those breeding on Sable Island.
A cladistic analysis of mtDNA data yielded three clades among northern seals: Phoca-Pusa-Halichoerus, Cystophora-Pagophilus, and Erignathus (Perry et al. 1995). Each clade may be regarded as a tribe of the subfamily Phocinae. The magnitude of the differences among Phoca, Pusa, and Halichoerus was on the same order as that between species and subspecies within the genus Odocoileus. Because Cystophora is the closest relative of Pagophilus, the latter cannot be regarded as congeneric with Phoca; the differences between the two are great enough to justify placing them in separate genera (Perry et al. 1995).
Mouchaty et al. (1995) examined the cytochrome b gene and found a close phylogenetic relationship between P. hispida and Halichoerus grypus, which, they noted, merits further study.