Sink or Swim: Strategies for Cost-Efficient Diving by Marine Mammals

Abstract

Locomotor activity by diving marine mammals is accomplished while breath-holding and often exceeds predicted aerobic capacities. Video sequences of freely diving seals and whales wearing submersible cameras reveal a behavioral strategy that improves energetic efficiency in these animals. Prolonged gliding (greater than 78% descent duration) occurred during dives exceeding 80 meters in depth. Gliding was attributed to buoyancy changes with lung compression at depth. By modifying locomotor patterns to take advantage of these physical changes, Weddell seals realized a 9.2 to 59.6% reduction in diving energetic costs. This energy-conserving strategy allows marine mammals to increase aerobic dive duration and achieve remarkable depths despite limited oxygen availability when submerged.

The foraging benefits of being fat in a highly migratory marine mammal

“…Previous studies suggest that marine mammals may reduce swimming costs by employing prolonged gliding aided by negative buoyancy during the descent phase of dives [15,16,22]. This was confirmed by experimental modification of buoyancy in seals [17,23].…”

“…During descent, the proportion of time spent in prolonged gliding remained high when seals were negatively buoyant (range ¼ 0.4-0.9; figure 2). This indicates that seals largely relied on negative buoyancy as the thrust force for gliding, which kept their stroking effort low [15,17]. In addition, descent pitch angles were steeper when seals were more buoyant (electronic supplementary material, figure S5), which might allow seals to descend with less stroking activity because a steeper pitch angle would bring the vector of forward motion closer to that of the force of gravity [16].…”

“…The relationship between buoyancy and swimming strategy may apply across a range of aquatic animals, from fishes to whales (e.g. fish [13,14], diving mammals [15][16][17], birds [18][19][20] and sea turtles [21]), representing transitions from & 2014 The Author(s) Published by the Royal Society. All rights reserved.…”

“…For statistical analysis, the strokes-per-metre values for each dive were averaged to obtain a daily mean strokes-per-metre. We calculated the proportion of time spent in prolonged gliding during the transit phases of each dive, because prolonged gliding is a key strategy to reduce swimming costs [15]. In this study, we defined prolonged gliding phases as any period during transit with no strokes for 5 s (the finest time resolution of the data from Stroke Loggers) or more.…”

Hyperbaric computed tomographic measurement of lung compression in seals and dolphins

“…Indirect measurements have suggested that the depth where gas exchange ceases is between 30m (Falke et al, 1985) and 70m (Ridgway and Howard, 1979), but direct measurements of animals diving with a lung volume of only 18% of TLC indicate that complete shunt may not occur until a depth of 170m (Kooyman and Sinnett, 1982). Studies of maximal depth of neutral buoyancy, which has to be at a depth less than atelectasis (Biuw et al, 2003;Skrovan et al, 1999;Williams et al, 2000), agree with the pulmonary shunt data published by Kooyman and Sinnett showing that the collapse occurs at depths below 100m (Kooyman and Sinnett, 1982). Our results using the hyperbaric chamber suggest these last estimates have worth.…”