Fig. 4. Transverse (A) and longitudinal (B) sections showing myotomal muscle thermal contours (yellow and red lines) for a 148-kg salmon shark (Lamna ditropis) swimming in 10°C water. Contour projections are modified from Carey and Teal (1969a) and Carey et al. (1985) and use a maximum red muscle (RM) temperature of 24°C. Sectors (S1—S6) show the extent of regional endothermy occurring in white muscle (WM) located at different distances from the RM (see Table 4). The transverse section shows the sites where the three WM samples were taken in relation to the body temperature gradient, with highest temperature occurring closest to the RM and lowest temperature near the skin. (C) Graphs show temperature effects on the activities of lactate dehydrogenase (LDH) and citrate synthase (CS) in WM at the three locations (same symbols as in A) of a 49-kg mako and 127-kg salmon shark. (Table 3 contains the full data set for all the sharks.)

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