A review of the taxonomy and nomenclature of North Pacific Harbour seals

Abstract

The previous multitude of taxa of North Pacific Harbour seals is referable to, at most, three forms: the ice‐inhabiting Larga seal,Phoca vitulina largha; the Insular seal of eastern Asia,P. v. stejnegeri; and the coastal Harbour seal of western North America,P. v. richardsi.In the breeding season,larghaoccurs on the pack ice of the Bering, Okhotsk, Japan, and Po Hai seas as adult pairs with single pup, whereasstejnegeriandrichardsiare associated with coastal and insular habitats, around the perimeter of the North Pacific Ocean from Hokkaido to Baja California (i.e. mostly well away from ice), and occur on land in dense aggregations of less than ten to more than a thousand animals. In general, where the ranges of thelarghaand thestejnegeri‐richardsiforms meet or overlap, their respective breeding seasons are about two months apart, which, together with the social and habitat differences, tends to result in reproductive isolation. Apparently, the young oflarghaare always born with a whitish lanugo, whereas those ofstejnegeriandrichardsiusually shed their lanugo (either whitish or mottled greyish)in uteroand are born with an adult‐like pelage. The adult pelage oflarghaseems always to be pale background with a spattering of small, blackish spots, whereas thatof stejnegeriandrichardsiranges from black with scattered whitish rings (dark phase) to pale with small black spots (light phase). Light phase animals usually differ fromlarghain having some whitish rings on the back. In body and skull size,stejnegeriexceeds the others, but in cranial characters,stejnegeriandrichardsiseem very similar and to differ mutually fromlarghain all respects. They also differ fromlarghain having abbreviated stylohyals, not connected to the bulla. The complex nomenclatural history of each taxon is reviewed, and the namelarghaPallas, 1811 is retained for the ice‐inhabiting form. For the insular form,stejnegeriAllen, 1902 has priority, and for the American coastal form,richardsi(Gray, 1864).Larghaoccurs as eight geographical populations that are morphologically alike, suggesting that they have been separated for a relatively short period in geologic time. Thestejnegeri‐richardsicomplex, conversely, shows a much greater degree of regional differentiation, as indicated by the frequency of occurrence of dark and light colour phases, but appears to be all of one polytypic, trans‐Pacific form, which is more similar to the North Atlantic Harbour seals than islargha.Althoughlarghahas usually been regarded as a subspecies ofP. vitulina, it seems advisable on the basis of this review to accord it specific rank.