SANTA CRUZ, CA--For years scientists have puzzled over the ability of dolphins, seals, and other marine mammals to perform long, deep dives that seem to exceed their aerobic capacities. Now, with the help of sophisticated instruments and video technology, a team of researchers has resolved the paradox and discovered a laid-back diving strategy that appears to be widespread among marine mammals.
The researchers studied Weddell seals hunting beneath the ice in the Antarctic, a northern elephant seal diving in Monterey Bay, a trained bottlenose dolphin diving offshore of San Diego, and a 100-ton blue whale traveling off the coast of northern California. Video cameras mounted on the animals' backs revealed that they all started their dives with a few powerful swimming strokes, then made the rest of the descent mostly in a relaxed glide.
"Basically, they're turning the motor on and off in the course of the dive, and that enables them to reduce oxygen consumption by 10 to 50 percent compared with what they would need if they swam all the way down," said Terrie Williams, an associate professor of biology at the University of California, Santa Cruz.
Williams, working with collaborators from several institutions, found that marine mammals take advantage of a change in buoyancy due to increasing pressure with depth, which enables them to sink effortlessly through the water. The researchers describe their findings in the April 7 issue of the journal Science. Williams's coauthors include UCSC biologists Burney Le Boeuf and Donald Croll, Randall Davis and Markus Horning of Texas A&M University, Lee Fuiman of the University of Texas at Austin, John Francis of the National Geographic Society, and John Calambokidis of Cascadia Research in Olympia, WA.
The researchers correlated video images of the diving animals with data from other instruments, including time-depth recorders. With the Weddell seals, the scientists were able to monito
Contact: Tim Stephens
University of California - Santa Cruz