MEAGHER, E/M; MCLELLAN, W/A; WESTGATE, A/J; WELLS, R/S; BLUM, J/E; PABST, D/A; UNC Wilmington; UNC Wilmington; Duke University; Chicago Zoological Society; UNC Wilmington; UNC Wilmington; ; : Seasonal differences in heat flux across multiple body surfaces in wild bottlenose dolphins (Tursiops truncatus)

Bottlenose dolphins use their appendages as thermal windows, allowing them to conserve or dissipate body heat. However, few direct measurements exist to clarify how wild dolphins utilize their appendages to control their body temperature. Bottlenose dolphins resident to Sarasota Bay, FL experienced water temperatures (T_w) that varied seasonally from 11^oC to 33^oC. We hypothesized that heat flux (W/m²) would decrease in these dolphins in winter, relative to summer, in response to decreased T_w. Simultaneous measurements of heat flux were collected at the lateral body wall (thoracic and tailstock) and thermal windows (dorsal fin, pectoral flipper, flukes) of dolphins that were investigated during health-monitoring events in June 2002, 2003 and 2004 (mean T_w=30.2 � 1.1^oC, n=38) and February 2003 and 2004 (mean T_w=17.0 � 1.3^oC, n=13). Mean heat flux values across lateral body wall sites were significantly higher in winter, relative to those measured in summer (Wilcoxon Rank Sum test, thoracic: p=0.0046, tailstock: p=0.0001), despite significantly thicker winter blubber layers at these sites. There were no differences between summer and winter heat flux values at thermal windows. These results suggest that bottlenose dolphins in Sarasota Bay do not necessarily respond to decreased T_w by decreasing heat loss across their body surface. Higher winter heat loss rates may reflect higher metabolic rates or a thermoregulatory response to an overinsulated body wall. Alternatively, these dolphins may use mechanisms such as enhanced respiratory heat loss or shifts to cooler microclimates to dissipate excess body heat in summer. These mechanisms are currently under investigation. NOAA Scientific Permit No. 522-1569.