NSF PR 00-18 - April 7, 2000
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Studies of Marine Mammals Indicate a "Breathtaking"
Ability to Dive to Great Depths
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.
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