TEMPORAL PATTERNS OF MILK-PRODUCTION IN ANTARCTIC FUR SEALS (ARCTOCEPHALUS-GAZELLA)

The timing of milk production in Antarctic fur seals was studied at Bi rd Island, South Georgia. Like all lactating otariid seals (Pinnipedia : Otariidae), Antarctic fur seal females alternate between short nursi ng periods ashore and regular foraging trips to sea. Females do not ne cessarily return to the colony with full mammae, which indicates that mammary volume capacity is unlikely to limit foraging trip duration. U pon arrival at the colony, milk fat (r(2) = 0.33, P < 0.04) and protei n (r(2) = 0.60, P < 0.002) content were positively correlated to the t ime spent at sea. A similar trend was observed in the milk produced on land. The rate of milk energy production was much lower at sea (5.02/-0.05 MJ . day(-1)) than on land (23.66+/-4.4 MJ . day(-1)). The rate of milk energy production during the foraging trip was negatively cor related to the time spent at sea (r(2) = 0.29, P < 0.05), whereas the rate of milk energy production on land was positively correlated (r(2) = 0.61, P < 0.001) to the duration of the preceding foraging trip. Th e total amount of milk energy delivered to the pup during each two-day nursing period was positively correlated (r(2) = 0.60, P < 0.002) to the duration of the previous foraging trip. The overall rate of milk e nergy delivery, however, was independent of foraging trip duration. Th is accords with previous observations that the growth rates of Antarct ic fur seal pups are unaffected by maternal foraging trip duration pat terns.