Water and Energy Flux in Elephant Seal Pups Fasting under Natural Conditions

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Abstract
Total water flux, energy utilization, and mass loss were measured in fasting, newly weaned elephant seal pups, Mirounga angustirostris, in their natural habitat over a period of 32-52 days. Animals lost mass exponentially averaging 5.3 ± 0.9 g· kg⁻¹· day⁻¹. At weaning body water comprised 40% of the total mass while the ratio of adipose to lean body tissue was approximately 1. The mean water turnover rate in all animals was very low, ∼13.0 ± 1.20 ml·liter⁻¹· day⁻¹, and was not affected by entry of the animal into water, supporting the hypothesis that seawater ingestion is not required for water balance. Average metabolic rates calculated from water turnover data were 167.6 ± 19.1 . The biological half-time of water, 53.5 ± 5.2 days, is about 2.5 times greater than that of starved harbor seals and significantly exceeds that reported for any other mammal. We conclude that a combination of behavioral and physiological water conservation mechanisms permit these animals to fast on land for up to 3 mo, deriving necessary water and energy from the oxidation of fat stores.