The relationship between heat flow and vasculature in the dorsal fin of wild bottlenose dolphins Tursiops truncatus.

The dorsal fin of the bottlenose dolphin Tursiops truncatus contains blood vessels that function either to conserve or to dissipate body heat. Prior studies have demonstrated that heat flux, measured from a single position on the dorsal fin, decreases during body cooling and diving bradycardia and increases after exercise and at the termination of the dive response. While prior studies attributed changes in heat flux to changes in the pattern of blood flow, none directly investigated the influence of vascular structures on heat flux across the dorsal fin. In this study we examined whether heat flux is higher directly over a superficial vein, compared to a position away from a vein, and investigated the temporal relationship between heart rate, respiration and heat flux. Simultaneous records of heat flux and skin temperature at three positions on the dorsal fins of 19 wild bottlenose dolphins (with the fin in air and submerged) were collected, together with heart rate and respiration. When the fin was submerged, heat flux values were highest over superficial veins, usually at the distal tip, suggesting convective delivery of heat, via blood, to the skin's surface. Conversely, in air there was no relationship between heat flux and superficial vasculature. The mean difference in heat flux (48 W m(-2)) measured between the three fin positions was often equal to or greater than the heat flux that had been recorded from a single position after exercising and diving in prior studies. Tachycardia at a respiratory event was not temporally related to an increase in heat flux across the dorsal fin. This study suggests that the dorsal fin is a spatially heterogeneous thermal surface and that patterns of heat flux are strongly influenced by underlying vasculature.