Mass Changes and Metabolism during the Perinatal Fast: A Comparison between Antarctic (Arctocephalus gazella) and Galápagos Fur Seals (Arctocephalus galapagoensis)

Abstract

Female mass loss and metabolic rate were measured along with changes in pup mass during the perinatal period in Antarctic and Galapagos fur seals. Antarctic fur seal females lost 3.15%, or 1.231 kg per day, of their initial body mass of roughly 39 kg. Heavier females gave birth to heavier young (r = .644, P < .05; n = 12) and lost significantly more mass per day than did smaller females (r = .796, P < .01; n = 12). In contrast, Galapagos fur seal females (37.4 kg) lost half as much mass per day (1.68% day⁻¹ 0.639 kg day⁻¹). Metabolic rates, determined by the doubly labeled water method, were considerably higher in Antarctic fur seals (4.56 W kg⁻¹) than Galapagos fur seals ( 1.48 W kg⁻¹). We suggest that the lower metabolic rate of Galapagos fur seal females is an adaptation to reduce thermal stress on land in the warm equatorial habitat. Measurements of metabolic rate from water influx overestimated metabolism measured with the doubly labeled water method by only 3.2% in Antarctic fur seals, while seawate...