Metabolic rate, heart rate, and tailbeat frequency during sustained swimming in the leopard shark Triakis...

Heart rate, metabolic rate, and tailbeat frequency were simultaneously recorded from seven leopard sharks (Triakis semifasciata) during steady swimming at controlled speeds to evaluate the usefulness of heart rate as a measure of field metabolic rate. Heart rate was monitored by acoustic telemetry using a frequency modulated ECG transmitter. Metabolic rate was measured as oxygen consumption in a swimming tunnel respirometer. For instrumented sharks, mean resting oxygen consumption rate and heart rate were 105.3 +/- 35.6 (SE) mg O2.kg-1.h-1 and 36.6 +/- 1.8 (SE) beats.min-1, respectively. While swimming at the maximum sustained speed (0.84 +/- 0.03 lengths.s-1) for 30-60 min, these rates were 229.3 +/- 13.2 mg O2.kg-1.h-1 and 46.9 +/- 0.9 beats.min-1. Although a significant linear regression was obtained between metabolic rate and heart rate, a low overall correlation coefficient may result from the existence of separate individual regressions and confounding changes in stroke volume and/or arteriovenous oxygen difference. Heart rate was approximately as closely correlated with oxygen consumption rate as swimming speed was. A significant linear relationship was obtained between tailbeat frequency and swimming speed to speeds of 0.75 lengths.s-1.