Aerobic Capacities of Freediving Mammals
Posted By Erik Seedhouse on 31 March 2003
Longer dives usually cause seals to exceed the ADL and use anaerobic respiration. Experimentally this is determined by blood sampling - an increase in blood lactate indicating the seal has used anaerobic respiration. Seals use different diving patterns in order to recover from any lactate that accumulates during an anaerobic dive. Weddell seals for example, will vary the length of the recovery period depending on the length of the dive. A series of long (about twenty minutes each) dives by these seals is followed by a sequence of short, aerobic dives that allow the accrued lactate in the blood to be gradually flushed out.
Energetic effectiveness is another strategy employed by seals, sea lions and whales in conserving oxygen. As might be expected, dive depth, and therefore distance traveled, affects the percentage of time available for gliding, the primary oxygen-conserving behavior employed by marine mammals. The percentage of time spent gliding during a descent increases significantly and nonlinearly with increasing dive depth and equates to a considerable energetic saving in terms of oxygen use.
Another mechanism available to seals is how it stores oxygen. Seals do not
use their lungs to store oxygen. As seen in the graph below, when diving,
there is significantly less oxygen in the lungs of a seal than the lungs of
a human. The lungs cannot store air as a seal dives because of the increased
risk of decompression sickness it would impose on the seal.
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