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ABSTRACT

During diving, marine mammals must rely on the efficient utilization of a limited oxygen reserve sequestered in the lungs, blood and muscles. To determine the effects of exercise and apnea on the use of these reserves, the marine biologists examined the physiological responses of adult bottlenose dolphins (Tursiopstruncatus) trained to breath-hold on the water surface or to dive to submerged targets at depths between 60 and 210 meters. Changes in blood lactate levels, in partial pressures of oxygen and carbon dioxide and in heart rate were assessed while the dolphins performed sedentary breath-holds. The effects of exercise on breath-hold capacity were examined by measuring heart rate and post-dive respiration rate and blood lactate concentration for dolphins diving in some part of Pacific Ocean within the Philippine Area of Responsibility. Ascent and descent rates, stroke frequency and swimming patterns were monitored during the dives. The results showed that lactate concentration was at rest and increased non-linearly with the duration of the sedentary breath-hold or dive. Lactate concentration was consistently higher for the diving animals’ at all comparable periods of apnea. Breakpoints in plots of lactate concentration and blood gas levels against breath-hold duration for sedentary breath-holding dolphins occurred between 200 and 240 seconds. In comparison, the calculated aerobic dive limit for adult dolphins was 268 seconds. Descent and ascent rates ranged from 1.5 to 2.5 meters during 210 meters dives and were often outside the predicted range for swimming at low energetic cost. Rather than constant propulsion, diving dolphins used interrupted modes of swimming, with more than 75 % of the final ascent spent gliding. Physiological and behavioral measurements from this study indicate that superimposing swimming exercise on apnea was