| Summary: | A weakness in predicting habitat change impacts in polar regions is that little is known about thermoregulatory energetics in high‐latitude seals. To better understand thermoregulatory range associated with the partitioned air‐water habitat of ice seals, we collected skin surface heat flux data from 42 free‐ranging Weddell seals over 1‐13 day deployments. We modeled total body heat dissipation from heat flux data to address the thresholds of basal versus activity‐derived heat loss over a range of swim speeds. As body size/condition affect heat loss and may manifest as altered thresholds for thermal homeostasis, we compared 4 life history categories—pups, juveniles, non‐reproductive adult females and post‐weaning females. Preliminary evidence indicates obligate heat dissipation, reflecting thermoregulatory costs, is elevated in water versus air, and locomotory heat generation offsets these costs. Dive activity‐heat loss relationships were compared among the 4 life history stages to detect differences in baseline obligate heat loss and threshold swim speeds for thermal substitution. Group differences were apparent under non‐steady state conditions such as transition from haul‐out to water, where post‐weaning females lost more heat than good condition skip breeder females (+40% W/m 2 heat loss). Juveniles, with limited blubber insulation, also lost more heat than pups on initial water entry. Continued efforts to quantify and model thermoregulatory thresholds will provide important insights into the ability of polar pinnipeds to respond to changing ice conditions.
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