The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth

During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5-50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9+/-7.3 to 126.2+/-23.1 W m(-)(2) and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0+/-2.6 beats min(-)(1), N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.