Comments: 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). See also Mouchaty et al. (1995) for phylogenetic information.
Two subspecies have been proposed (E. b. barbatus of the Laptev and Barents seas and North Atlantic Ocean, and E. b. nauticus of the Bering and Okhotsk seas and Arctic Ocean; however, "the geographical limits of the putative subspecies are vague, and the morphological distinctions are meager" (Reeves et al. 1992). NMFS (2010) accepted the validity of these two subspecies, and further concluded that E. b. nauticus consists of two distinct population segments (DPSs), the Beringia DPS and the khotsk DPS.