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April 11, 2000 - VOL. 27, NO. 13

Mysteries of the Deep: Scientists solve centuries-old puzzle of how marine mammals stay submerged without breathing for astonishingly long periods


Caroline Ladhani, College of Natural Sciences


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Dr. Lee A. Fuiman of the UT Austin department of marine science is among researchers from Texas, Washington and California who have solved a mystery that has taunted observers of seals, whales and other marine mammals for centuries.

In an article published Friday (April 7) in the journal Science, the research team reveals how marine mammals can stay submerged without breathing for astonishingly long periods of time.

Certain marine mammals appear to use more energy than puzzled scientists believe can be stored in their bodies while they are swimming, diving and moving around underwater. For example, the Weddell seal in Antarctica can move under water for as long as 80 minutes without coming up for air.

The researchers attached video cameras and computers to seals, whales and dolphins to record information on their underwater movements. Swimming requires a lot of energy, and they discovered that the animals are not always swimming when they are underwater. Instead, they are conserving energy by gliding.

Fuiman, a behavioral ecologist with UT Austin's Marine Science Institute at Port Aransas, said previous estimates of how much oxygen the marine mammals can store in their bodies "is less than how much oxygen they would be expending if they were swimming the whole time they were submerged. They are doing something they shouldn't be able to do."

Fuiman said the key to the mystery is that the animals can descend several hundred meters by gliding, without propelling themselves. "Our assumption that they were swimming constantly while they were submerged was wrong," he said.

The "stars" of the research show included three adult Weddell seals at McMurdo Station, Antarctica, who dove down through an isolated hole in the ice to depths of nearly 700 meters; one juvenile northern elephant seal, diving freely in Monterey Bay; one adult bottlenose dolphin trained to dive to various submerged targets near San Diego; and one adult blue whale diving along Cordell Bank along the Northern California shore.

Dr. Terrie M. Williams of the University of California at Santa Cruz led the research team, which included Fuiman, Dr. R. W. Davis and Dr. M. Horning, department of marine biology, Texas A&M University; Dr. J. Francis of the Committee for Research and Exploration, National Geographic Society; Dr. B.J. Le Boeuf and Dr. D.A. Croll, department of biology, UC-Santa Cruz; and Dr.J. Calambokidis, Cascadia Research, Olympia, Wash.

In the past, studies had been performed on diving mammals as they came up to the surface of the water to breathe air. Scientists would put smaller instruments on them that could measure only swimming speed, how long they had been submerged and the depth at which they been swimming.

For this project, each of the animals dove with a video camera attached to its head or back, plus a computer strapped to its back. This equipment allowed the scientists to study locomotor strategies during the deep dives, including frequency and amplitude of flipper strokes, glide sequences and swimming modes.

The scientists pointed the video camera either forward, to record head movement, or backward to record any tail or hind flipper movement. "It was a matter of watching the videos -- seeing the animal dive without moving its tail. We're watching the depth increase, but the animal is not swimming," Fuiman said.



April 11, 2000
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