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

During diving, marine mammals initiate a series of cardiovascular changes t hat 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 ca pabilities during submergence. Here, we demonstrate how the thermoregulator y responses of bottlenose dolphins (Tursiops truncatus) are coordinated wit h the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water s urface, 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 act ivity. 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 excee ding pre-dive values occurred at both sites upon resurfacing. Changes in he art 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% duri ng dives to 50 m and immediately returned to near resting levels upon resur facing. These studies indicate that heat dissipation by dolphins is attenua ted during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation i s reduced.