Seal Cams Reveal Fight For Breathing Holes

Dec. 8, 2004 — -- Antarctica's landscape is so harsh it has humbled even the most seasoned adventurers and made prying knowledge from the continent a dangerous enterprise. Little is known about what lies beneath its giant sheets of ice and even less about the few animals that call the frozen continent home -- until now.

The Weddell seal is the only mammal that inhabits Antarctica year-round. Its ability to hunt, reproduce and survive in the coldest, driest, windiest continent on Earth has intrigued scientists for decades. A new book, "The Hunter's Breath" by Terrie Williams, sheds light on this remarkable animal and reveals that even this hardy species has felt the effects of global warming.

During an expedition in 2001 a group of scientists, including Williams, a University of California at Santa Cruz marine biologist, attached tiny cameras to more than 20 of the animals to get a seal's-eye view of the world below the ice.

The research revealed that Weddell seals have the ability to stay underwater for upward of an hour and they can dive down to depths of nearly a mile with no adverse effects. Their front teeth are essential to their survival under the ice since they use them as ice picks to chip away at frozen-over breathing holes.

Most importantly, the team learned that Weddell seals' survival and hunting ability were limited when warming caused icebergs to break off the continent's shelf.

Battle to Breathe

During the expedition, the largest iceberg recorded in Antarctic water, estimated at over 1,000 feet thick and 170 miles long, nearly the size of Rhode Island, slammed into the permanent ice shelf the Weddell seals called home. Some scientists believe that global warming was the main factor that led B-15 to separate from the ice shelf. Upon its impact it shattered the ice shelf in some areas into deep crevasses, trapping penguins. In other places solid ice blocked pregnant Weddell seals from reaching nursery areas.

"Local, national and international news called B-15 a 'giant,' a 'geological curiosity,' and a 'testament to global warming.' The eight members of our research team had other names for B-15. We viewed the iceberg as an immediate and dangerous threat that would have severe ramifications for our expedition," Williams writes in her book.

The same could be said for the effect on the seals.

The Weddell seals rely on breathing holes for survival, but the arrival of B-15 compacted much of the normal ice flows and drastically limited the number of breathing holes available. From the camera attached to the seals, the researchers learned that Weddell seals do not fight over food sources, like most other predatory mammals. Instead, they fight over access to breathing holes and that is the main determinate of any hunting expedition.

The animals have an innate ability to track how far and long they can go without air. In one case a seal traveled nearly two miles underwater without access to a breathing hole. Aware that his air supply was halfway depleted, he turned around and returned to his initial breathing hole, knowing he had just enough time to get back.

Exploring the Unknown

For the research team, the seals turned out to be perfect partners. Weddell seals have no predators in Antarctica -- contrary to popular belief, polar bears do not live in the Antarctic. With no natural predators, the Weddell seals were apparently unfazed by the people studying them.

At times the seals were even curious and would pop by the man-made breathing hole the scientists had dug out at their camp. These factors made placement of the cameras far easier than the researchers had expected.

The team's insight into the animal's underwater behavior was novel since intense water pressure prevents scuba divers from diving to the depth that the seals reach and underwater robots don't have the agility to maneuver around the icebergs.

"More is known about the surface of Mars than the waters below Antarctica," Williams said.

By attaching small cameras to more than 20 Weddell seals, the researchers could see the first pictures of the previously unreachable depths and observe the social lives of the seals deep below the ice.