Meeting Abstract
Weddell seals (Leptonychotes weddellii), the southernmost breeding mammals, are born into one of the most challenging thermal environments on the planet. During dependence, pups must survive on ice and in water and concurrently shift from the use of fur to a reliance on blubber for insulation. We examined the thermal and energetic costs associated with development and thermoregulation in Weddell seal pups. Mass-specific metabolic rate (MR) in air was measured longitudinally for 10 pups every 2w, starting at 1w of age through the transition to independence (7w); MR in water was measured in the same pups starting at 3w. We assessed molt status (amount of lanugo) and estimated body composition (blubber vs. lean mass) using an elliptical cones model. There was a high degree of individual variability in MR in air for 1w old pups, but it tended to decrease slightly from 1-7w of age. MR in water declined from 3w to 7w for some pups and remained stable for others. By 5w the difference between MR in air and in water was marginal for all pups. Timing and duration of the molt were highly variable among individuals. All pups gained mass from 1-5w of age (2.02 ± 0.09 kg day-1) and blubber proportion increased from 1-3w (25%-38% of body mass). Blubber proportion remained steady from 3-5w (38%-40% of body mass) because pups gained proportionally more lean mass (61% of total mass gained). Timing of MR equivalence in air and water did not vary with estimated body composition, but it did correlate with molt status. These results indicate Weddell seal pups have developed thermal capabilities by ~5w of age to combat increased heat loss in water, independent of body composition.
