Cranial morphometrics of the southern fur seals Arctocephalus forsteri and A. pusillus (Carnivora : Otariidae)

Abstract

The identification and classification of unknown specimens of Arctocephalus from regions of Australasia has proven difficult. Skulls from the New Zealand fur seal (Arctocephalus forsteri) and the Australian fur seal (A. pusillus doriferus), and data from specimens of the South African fur seal (A. p. pusillus), were examined. A visual method was devised to identify and separate A. p. doriferus from A. forsteri for both sexes and for most physiological age-groups. A statistical method for morphometric separation of these species was applied to adult specimens. Characteristics of males and females for both species fell into two broad categories: sexually dimorphic – mainly those characters that increase the ability of males to hold and defend territories; and non-dimorphic – those of functional importance. Studies of geographical variation showed that adult male A. forsteri from Australia were generally larger than those from Macquarie Island and New Zealand. Characteristics of A. p. doriferus were generally larger than those of A. p. pusillus. Nine specimens of New Zealand fur seals were morphologically different from the typical A. forsteri, which indicates the presence of extreme outliers or hybrids in the sample.