Climate change is expected to increase the frequency and duration of long-distance swims by polar bears (Ursus maritimus). The energetic costs of such swims are assumed to be large, however, no estimates of metabolic costs of swimming for polar bears are available. Here, I use data on internal body temperature and external ambient temperature for two swimming polar bears, combined with mathematical modeling of heat production and of heat conduction to the surrounding water, to estimate the metabolic rate of swimming. Using this metabolic rate, I then examine the relative heat production and heat loss for bears of a range of sizes and body conditions. I calculated overall mean metabolic rate for a swimming bear to be 2.75 ml O2 g−1 h−1, which is generally higher than metabolic rates previously reported for walking polar bears. When compared at the same movement rate, the cost of transport for swimming was estimated to be approximately 5× that of walking. I further show that for small bears (less than approx. 145 cm body length or 90 kg) and bears in poor body condition, heat loss while swimming in cold Arctic waters should exceed heat production, and long swims should therefore not be thermodynamically sustainable. These results support previous claims that increasing frequency and duration of long-distance swims in polar bears is energetically stressful. Energetic and thermodynamic costs of long swims may be further exacerbated by recent declines in body condition that have been documented due to climate warming.
Polar Biology – Springer Journals
Published: Sep 16, 2017
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