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The energy expenditure of breeding male harbour seals, Phoca vitulina, on Sable Island, Nova Scotia, was investigated by measuring changes in body mass, body composition, and water flux using isotope dilution. Seals lost 0.47% +/- 0.04% (n = 34) of their initial mass per day during the breeding season (4 wk), and fat, water, and protein accounted for 64.3% +/- 4.8%, 27.8% +/- 3.3%, and 6.9% +/- 1.4% of this mass loss, respectively (n = 31). Total energy expenditure was estimated as 33.3 +/- 1.9 MJ d(-1), or 3.9 +/- 0.2 W kg(-1) (n = 17), similar to rates measured in terrestrially mating pinniped species. However, unlike terrestrially mating pinnipeds, male harbour seals did not fast during the breeding season, and energy intake from foraging accounted for 61.8% +/- 4.0% of the total energy expended. Males derived most of their expended energy from food intake early in the breeding season. However, as oestrus females became increasingly available, reduced rates of food intake in males were coupled with increased rates of total energy expenditure. Larger males expended significantly more energy from body stores and more total energy than smaller males. Male harbour seals appeared to balance the energetic costs of reproduction against the constraints of small body size by foraging during deep-diving trips before the appearance of oestrus females and by opportunistic feeding throughout the breeding season while at sea. We suggest that size dimorphism may be less pronounced in aquatically mating pinnipeds partly because the temporal and spatial separation of foraging and reproduction is less distinct than it is for terrestrially breeding pinnipeds.

Harp seals (Phoca groenlandica) give birth on pack ice and nurse their pups for about 13 d. We hypothesized that lactating females would transfer milk and energy to pups at a high rate to compensate for the brevity of lactation. To test this hypothesis, the milk intake of five pups was measured over a 6-8-d period after administration of deuterium oxide; the initial age of pups was estimated to range from 0 to 5 d postpartum. Body water content of 17 pups was also measured by isotope dilution, and body composition of 12 pups was determined by chemical analysis. The proximate composition of harp seal milk (n = 21) was also assayed. Harp seal pups contained little fat (3%) at birth, but 61% of the increase in body mass (average 2.3 kg/d) was fat, with the result that fat accounted for 47% of body mass at weaning. Body water estimated by isotope dilution was not significantly different from that measured directly (n = 9 paired samples); water composed 72% of lean body mass. From birth to weaning, milk lipid ...

Hooded seals (Cystophora cristata) have a lactation period of 4 d. The rate of milk energy transfer must be very high to ensure that pups are weaned with sufficient energy reserves to withstand the lengthy postweaning fast. Milk energy transfer was measured by isotope dilution (n = 6), and energy deposition was assayed by chemical analysis of pups at birth (n = 4) and weaning (n = 5). Estimates of body water content obtained by isotope dilution and direct analysis were not significantly different. Water constituted only 71.7% ± 0.50% (SE) of lean body mass at birth, indicating developmental maturity. Newborn pups were also high in fat (14.0% ± 0.78%) and energy (10.1 ± 0.25 MJ/kg). Pups consumed 7.52 ± 0.469 kg/d milk containing 187 ± 11.6 MJ/d. Total milk and energy yields were estimated as 30.1 kg and 746 MJ. Pups deposited 88% of ingested fat, 41% of protein, and 84% of energy. Of the weight gain, 82% was fat. The energy content of pups increased nearly fourfold from birth to weaning, but protein conte...

In phocid species in which females fast throughout lactation, maternal energy reserves at parturition must support lactation. Thus, differences in body size and energy stores may influence the magn...

Isotope dilution was used to measure milk intake of 43 California sea lion pups on San Nicolas Island, California, from 1982 to 1984. Deuterium concentration was monitored in serial blood samples collected at about 5-day intervals for 3 wk after isotope administration. Estimated milk intakes differed significantly between male (723 ± 31.0 g ․ day⁻¹) and female (609 ± 24.0 g ․ day⁻¹) pups but did not increase from the first to second month postpartum. On a metabolic size basis (weight0.83), gross energy intakes did not differ between male and female pups but did differ between years, apparently as a consequence of the 1983 El Nino. The mean energy intakes (kcal ․ day⁻¹) of sea lion pups in the first (61 · W0.83) and second (308 · W0.83) months were high relative to terrestrial species. Regression of energy intake on growth rate predicted that maintenance energy requirements (kcal ․ day⁻¹) were also high (168 and 252 · W0.83 in the first and second months). The fact that California sea lion pups devote a la...