Studies of marine mammals indicate a "breathtaking" ability to dive to great depths

April 09, 2000

When it comes to diving deeply, marine mammals as different as seals and blue whales employ the same physiological adaptations to allow them to travel the maximum distance with minimum effort. So say researchers funded by the National Science Foundation (NSF), who studied the behavior of Weddell seals in Antarctica.

Using a miniature video system and data cameras and data recorders carried by the animals themselves, the NSF-funded research team of Terrie Williams of the University of California at Santa Cruz, Randall Davis and Markus Horning of Texas A&M University at Galveston, and Lee Fuiman of the University of Texas at Austin was able to monitor the animals' heart rates and oxygen consumption as they used their flippers. The team also measured oxygen consumption of these animals during their dives. They discovered that the seals, like the other animals studied, began their descent with a few powerful strokes and then continued down mostly in a relaxed glide, which greatly reduced their demand for oxygen.

The scientists describe their findings in the April 7 issue of Science.

The team studied Weddell seals near McMurdo Station, the NSF's principal scientific station in Antarctica as part of a larger study of the diving physiology of marine mammals. Working on the sea ice in McMurdo Sound, they drilled through 15 feet of ice in sub-zero temperatures to work with the seals at an isolated breathing hole.

The larger study to which Williams, Fuiman and Davis contributed looked at similarities in the abilities of a range of marine mammals to dive almost effortlessly to great depths. In addition to Weddells, other research teams studied the behavior of a northern elephant seal diving in Monterey Bay, Calif., a trained bottlenose dolphin diving offshore of San Diego, and a 100-ton blue whale traveling off the coast of northern California.

The range of animals exhibiting the same diving behavior was striking, even though whales and dolphins evolved independently from seals and use quite different mechanisms to propel themselves through the water. Despite their diversity, these and other marine mammals share an anatomical feature that makes a gliding descent possible and also protects them from getting the bends.

In humans and other land animals, air gets trapped as the lungs are compressed in a dive, forcing nitrogen into the bloodstream, which can produce a painful and often life-threatening condition known as "the bends."

Although they evolved along separate lines, both whales and seals apparently developed lungs that collapse progressively as water pressure increases so that air is forced out and into the upper part of the respiratory system. As the increasing pressure compresses the animals' body and the air in its respiratory system into a smaller and smaller volume, they become less buoyant.

By conserving energy through gliding on the way down, the animals are able to extend their dives. Weddell seals can achieve an estimated energy savings of nine percent to 60 percent over continuous swimming. This translates into an additional 7.5 minutes underwater.
NSF is an independent federal agency which supports fundamental research and education across all fields of science and engineering, with an annual budget of about $4 billion. NSF funds reach all 50 states, through grants to about 1,600 universities and institutions nationwide. Each year, NSF receives about 30,000 competitive requests for funding, and makes about 10,000 new funding awards.

National Science Foundation

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