| dc.description.abstract | 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. | en_US |
