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

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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, largha occurs on the pack ice of the Bering, Okhotsk, Japan, and Po Hai seas as adult pairs with single pup, whereas stejnegeri and richardsi are 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 the largha and the stejnegeri-richardsi forms 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 of largha are always born with a whitish lanugo, whereas those of stejnegeri and richardsi usually shed their lanugo (either whitish or mottled greyish) in utero and are born with an adult-like pelage. The adult pelage of largha seems always to be pale background with a spattering of small, blackish spots, whereas that of stejnegeri and richardsi ranges from black with scattered whitish rings (dark phase) to pale with small black spots (light phase). Light phase animals usually differ from largha in having some whitish rings on the back. In body and skull size, stejnegeri exceeds the others, but in cranial characters, stejnegeri and richardsi seem very similar and to differ mutually from largha in all respects. They also differ from largha in having abbreviated stylohyals, not connected to the bulla. The complex nomenclatural history of each taxon is reviewed, and the name largha Pallas, 1811 is retained for the ice-inhabiting form. For the insular form, stejnegeri Allen, 1902 has priority, and for the American coastal form, richardsi (Gray, 1864). Largha occurs as eight geographical populations that are morphologically alike, suggesting that they have been separated for a relatively short period in geologic time. The stejnegeri-richardsi complex, 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 is largha. Although largha has usually been regarded as a subspecies of P. vitulina, it seems advisable on the basis of this review to accord it specific rank.

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