Growth of New Zealand fur seal pups

The growth of pups of the New Zealand fur seal Arctocephalus forsteri (Lesson, 1828) on Taumaka, Open Bay Islands, Westland, New Zealand (43° 52’ S, 168° 53’ E) is described. The weights and curvilinear lengths of 1286 live pups were measured during January (308 pups), early and late February (515 and 399 pups, respectively) and August (64 pups), when aged approximately 40, 50, 60 and 240 days, respectively.

Males were heavier and longer than females at 40, 50, and 60 days, but sexual dimorphism was not evident in the small sample of pups aged 240 days. From birth to 60 days males gained an average of 74 g and 3.7 mm per day, and females 61 g and 3.5 mm per day. However, from birth to 240 days both sexes gained an average of 24 g and 8.6 mm per day. Pups increased their birth weight of 3.5 kg by 50% in 18 days and 100% in 55 days. Five individuals weighed on day 8 had increased their birth weights by 18–29%. Fourteen pups, weighed irregularly between 8 and 44 days of age, gained weight rapidly when their mothers were present, but lost weight quickly during the females’ absences.