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Water-tunnel studies of heat balance in swimming mako sharks

Diego Bernal^*, Chugey Sepulveda and Jeffrey B. Graham

Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0204, USA

View larger version (36K): [in a new window]   Fig. 1. (A) Diagram of a mako shark showing the positions of the temperature probes. The modified temperature loggers associated with the red (RM) and white (WM) muscle thermistors were attached to the body surface (1 and 2). The position of the stomach temperature logger is indicated by ST. (B) Transverse section (at 45 % FL, where FL is fork length) of a 10 kg mako shark showing the location of the heat-exchanging retia, the relative vertical positions of the RM and WM thermocouples and thermistors and the temperature logger in the stomach (ST). Note that the WM probes were posterior to the RM probes by 2 % FL.

View larger version (24K): [in a new window]   Fig. 2. Complete recordings of red (RM) and white (WM) muscle and stomach temperatures (T) for a 6.9 kg mako shark during its initial adjustment to the water tunnel, the post-surgery recovery period, the initial cooling phase and the three thermal cycles. Note that the time scale reflects pre- and post-surgery periods. The values marked with an asterisk are the estimated values for thermal equilibrium (Te) in each of the three warming phases, and the horizontal arrows show the Te for the cooling phases.

View larger version (34K): [in a new window]   Fig. 3. Temperature changes in the red muscle (RM; bold tracing) and stomach (ST; light tracing) of five mako sharks. The dotted line represents the ambient water temperature. Insets for the 10.9 kg mako recording show RM temperature detail and the possible thermal notch during the onset of cooling cycles 2 (left-hand inset) and 3 (right-hand inset) (see Discussion).

View larger version (12K): [in a new window]   Fig. 4. Comparison of the red muscle cooling and warming rates of a 10.7 kg swimming mako shark (A) and of its post-mortem body (B). The dashed line represents ambient water temperature and the solid line is red muscle temperature.

View larger version (18K): [in a new window]   Fig. 5. Relationship between ambient water temperature (Ta) and red muscle temperature (TRM) determined for mako sharks weighing 5–13.6 kg and swimming steadily at 0.3–0.6 L s–1: TRM=6.18+(0.76±0.11)Ta (mean ± 95 % confidence interval; r2=0.90, N=26). The dashed line represents the Ta/TRM regression determined for decked mako sharks: TRM=13.8+(0.513±0.22)Ta [mean ± 95 % confidence interval; r2=0.36, N=38) (Carey et al., 1985)].