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

Erin M. Meagher^1,*, William A. McLellan¹, Andrew J. Westgate², Randall S. Wells³, Dargan Frierson, Jr⁴ and D. Ann Pabst¹

¹ University of North Carolina at Wilmington, Department of Biological Sciences and Center for Marine Science Research, 601 South College Road, Wilmington, NC 28403, USA
² Duke University Marine Laboratory, Duke Marine Lab Road, Beaufort, NC 28516, USA
³ Chicago Zoological Society, c/o Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
⁴ University of North Carolina at Wilmington, Department of Mathematics and Statistics, 601 South College Road, Wilmington, NC 28403, USA

View larger version (28K): [in a new window]   Fig. 1. Schematic representations of countercurrent heat exchangers in the appendages of a bottlenose dolphin. Cross-sections through (A) the dorsal fin, (B) the pectoral flipper and (C) the flukes. Inset below shows the positions of the cross-sections. Deep venous channels form peri-arterial venous retia (PAVR) surrounding central arteries (D). Superficial veins lie deep to the epidermis (thick black line) (modified from Pabst et al., 1999).

View larger version (82K): [in a new window]   Fig. 2. Infrared thermal image of a bottlenose dolphin dorsal fin in Sarasota, FL, USA (FLIR systems AGEMA 570 IR Camera, Secaucus, NJ, USA). The white line has been added to outline the contour of the dorsal fin. Superficial veins are visible as the lighter (warmer) lines running from the distal tip and trailing edge of the fin to the base of the fin.

View larger version (27K): [in a new window]   Fig. 3. Schematic representation of the heat flux harness placed on the dorsal fin of a bottlenose dolphin. (A) The harness, with a heat flux transducer attached to the Fluke Hydra data logger. (B) Locations of the heat flux transducers within the harness, which can change laterally and vertically. (C) The harness in a cross-sectional view. The heat flux transducer illustrated is placed directly over a superficial vein.

View larger version (29K): [in a new window]   Fig. 4. Representative data record (for FB 155). The three lines represent the different fin positions. Con, a position at the center of the fin directly over a superficial vein; Don, a position at the distal tip of the fin directly over a superficial vein; Coff, a position at the center of the fin away from superficial veins. The data streams begin recording with the dorsal fin in air. At fin submergence, all three heat flux values increase, while skin temperature values simultaneously drop. The two areas between the vertical dotted lines represent the 2 min segments of the record analyzed.

View larger version (28K): [in a new window]   Fig. 5. Representative record of heart rate and respiration (for FB117). The diamonds represent respiratory events. Vertical lines are added to the beginning of the data record to illustrate the temporal correlation between respiration and tachycardia. The heart rate data have been smoothed with a spline (=10, r2=0.83) (JMP IN) to simplify visualization of the correlation. Smoothed data were not used for actual heart rate calculations (see Table 5).

View larger version (25K): [in a new window]   Fig. 6. Representative record of heat flux, heart rate and respiration for the dorsal fin in air (FB 109). The diamonds represent respiratory events. Vertical lines are added to the beginning of the data record at each respiratory event to aid in the visual alignment of synchronous records. The heart rate data have been smoothed with a spline (=100, r2=0.49) (JMP IN) to simplify visualization. Con, a position at the center of the fin directly over a superficial vein; Don, a position at the distal tip of the fin directly over a superficial vein; Coff, a position at the center of the fin away from superficial veins.