INTERANNUAL AND INTRAANNUAL VARIATION IN MILK-COMPOSITION IN ANTARCTIC FUR SEALS (ARCTOCEPHALUS-GAZELLA)

The inter- and intra-annual variation in milk composition in Antarctic fur seals (Arctocephalus gazella) was investigated over three consecu tive lactation periods (1990-1992) at Bird Island, South Georgia, whic h included one period of low food availability. One hundred and ninety -two milk samples were collected from 154 individuals. The mean milk c omposition was 40.5% +/- 0.5% lipid 10.4% +/- 0.2% protein, 44.8% +/- 0.6% water, 0.133% +/- 0.005% carbohydrate, and 0.694% +/- 0.125% ash. Lipids contributed most (> 70%) of the gross energy of the milk. Wate r content could be used to predict lipid (r(2) = 0.83) and protein (r( 2) = 0.13) content, but it could be used to predict gross energy conte nt with the greatest accuracy of all (r(2) = 0.97). Stage of lactation , maternal mass, and year of sampling accounted for 27% of the observe d variability in gross energy content. Following the perinatal period, milk lipid and gross energy content increased throughout lactation in all years, whereas water content decreased. Protein content decreased throughout lactation in 1990 bur increased in the following 2 yr. Mil k lipid and protein content decreased by as much as 14% and 5%, respec tively, during each 1-2-d lactation bout. Minor, though significant, v ariation was found between the composition of milk collected from diff erent mammae within individuals. The changes in composition observed b oth within and between lactation periods, and the level of inter- and intraindividual variation, emphasize the need for extensive sampling i n order to describe adequately milk composition in otariids.