THEORETICAL HEAT-FLUX IN WATER AND HABITAT SELECTION OF PHOCID SEALS AND BELUGA WHALES DURING THE ANNUAL MOLT

The heat flux of marine mammals in water during the annual molt is estimated with theoretical calculations. The model is applied to typical small (the harbor seal, Phoca vitulina) and large (the southern elephant seal, Mirounga leonina) phocid seal and to the only cetacean known to molt annually, the beluga whale (Delphinapterus leucas). The results suggest that phocid seals could tolerate the heat flux associated with molting in water, but at a high energetic cost and only in relatively warm water temperatures, which are unlikely to be encountered. This agrees with the view that phocid seals must become terrestrial during the molt to satisfy the thermal requirements of their epidermis. The results also suggest that belugas would be able to molt in water, and would be thermoneutral while molting in water temperatures of 5 degrees C or higher. Movement into warm water estuaries during the molt would, however, allow them either to save energy or to molt more rapidly than if they stayed in colder open waters. While there is apparently some thermal benefit associated with fresh water compared to salt water, this would occur only under conditions that are unlikely to be encountered by belugas in the wild.