The respiratory physiology, heart rates and metabolic rates of two captive
juvenile male harbour porpoises (both 28 kg) were measured using a rapid-re
sponse respiratory gas analysis system in the laboratory. Breath-hold durat
ions in the laboratory (12 +/- 0.3 s, mean +/- SEM) were shorter than field
observations. although a few breath-holds of over 40 s were recorded. The
mean percentage time spent submerged was 89 +/- 0.4%. Relative to similarly
-sized terrestrial mammals, the respiratory frequency was low (4.9 +/- 0.19
breaths min(-1)) but with high tidal volumes (1.1 +/- 0.01 l), enabling a
comparatively high minute rate of gas exchange. Oxygen consumption under th
ese experimental conditions (247 +/- 13.8 ml O-2. min(-1)) was 1.9-fold hig
her than predicted by standard scaling relations. These data together with
an estimate of the total oxygen stores predicted an aerobic dive limit of 5
.4 min. The peak end-tidal O-2 values were related to the length of the pre
vious breath-hold, demonstrating the increased oxygen uptake from the lung
for the longer dives. Blood oxygen capacity was 23.5 +/- 1.0 ml.100 ml(-1),
and the oxygen affinity was high, enabling rapid oxygen loading during ven
tilation.