THE ENERGETICS OF HARBOR SEALS IN AIR AND IN WATER WITH SPECIAL CONSIDERATION OF SEASONAL CHANGES

Abstract

The energetics of six harbor seals in air at temperatures from 25 °C to −20 °C and in water from 25 °C to 0 °C was studied in animals acclimatized to summer conditions at Woods Hole, Mass. Over the above temperature range, the temperature of skin of the back cooled from about 35° to 1° with lowering temperature of the medium. Temperatures of the flippers were less dependent upon the surroundings than those of the body skin. The dependence of metabolism upon temperature was operative below 2 °C in air and below 20 °C in water (the critical temperatures), but the body skin temperature at these critical temperatures was the same, viz. 21 °C. Metabolism in air and in water was the same over the range of comparable skin temperatures. Body insulation was equal in air and in water at the respective critical temperatures. The insulation index of the air was approximately 20 times that of the water. Heat conductivity of living blubber to water averaged 2.5 cal/cm2/hr/°C, which exceeded that reported for dead blubber by about 50%.When compared with seals tested at St. Andrews during December, summer seals had a higher critical temperature, a lower body insulation index at the critical temperature, and a warmer body skin temperature for the same metabolic rate. No seasonal changes were found in thermoneutral metabolic rate, and no discernible changes in skin temperatures or in thermal gradients in the blubber.