MILK CONSUMPTION AND GROWTH EFFICIENCY IN ANTARCTIC FUR-SEAL (ARCTOCEPHALUS-GAZELLA) PUPS

The body composition, milk consumption, and growth efficiency of Antar ctic fur seal (Arctocephalus gazella) pups were measured over three co nsecutive lactation periods (1990-1992) at Bird Island, South Georgia. The body composition of pups differed between the sexes; whereas for any given age females were lighter than males, they had proportionatel y higher body lipid reserves than males. Milk consumption was determin ed on 388 occasions in 177 pups. Mean estimates of milk consumption ra nged from 2.5 to 3.2 kg (42-53 MJ) during the 6-day perinatal period a nd from 2.9 to 3.6 kg (49-68 MJ) during the 1- to 2-day maternal atten dance periods (feeding bouts). There were no differences in milk consu mption between the sexes in any year. Both per-bout and per-day milk c onsumption increased steadily with age before decreasing significantly in the last 30-40 days of lactation. Per-bout milk consumption was po sitively related to the duration of the maternal foraging trip and att endance cycle, and both per-bout and per-day milk consumption were rel ated to pup mass. Pups of both sexes consume the same amount of milk, but males direct more of their milk consumption into lean tissue growt h than females, which accumulate greater adipose stores. Therefore, ma ss and mass changes may not be appropriate parameters for investigatin g differential maternal investment between the sexes in otariid pups.