Thermoregulation of juvenile grey seals, Halichoerus grypus, in air

Metabolic rate, core temperature, and duration of sleep-related apnea events were monitored in three juvenile grey seals (Halichoerus grypus) aged 7-19 months (49-78 kg), at ambient air temperatures ranging from -18 degrees C to 35 degrees C. At low temperatures, only one seal increased its metabolic rate (at -18 degrees C), whereas at high temperatures (up to 35 degrees C) none of the three animals increased its metabolic rate. Nonetheless, seals usually became hyperthermic when they were subjected to air temperatures of 30 degrees C or higher. There was no indication that the duration of sleep-related apnea was greater at higher temperatures. The sleeping metabolic rate was significantly lower (20%) than the resting level. A metabolic depression associated with sleep may be advantageous at higher temperatures, reducing the internal heat load of the animal. These results suggest that cold-ware; adaptations of juvenile grey seals do not interfere with their ability to cope with higher air temperatures. Also, such animals should not be directly limited in their distribution by either high or low ambient air temperatures.