The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Îles Crozet.

The period of maternal dependence is a time during which mammalian infants must optimize both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater (t[SUB28]=2.73, P<0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t[SUB26]=3.82, P<0.001) in-air resting metabolic rates (RMR; 17.1 ± 0.6 mi O[SUB2] kg[SUP-1] min[SUP-1] than subantarctic fur seal pups (14.1 ± 0.5 mi O[SUB2] kg[SUP-1] min[SUP-1]). While in-water standard metabolic rate (SMR; 22.9±2.5 ml O[SUB2] kg[SUP-1] min[SUP-1) was greater than in-air RMR for Antarctic fur seal pups (t[SUB9] = 2.59, P<0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups (t[SUB12] = 0.82, P > 0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. [ABSTRACT FROM AUTHOR]