A new long-term study looking at the elusive Cuvier's beaked whale reveals the deepest and longest dives ever seen among mammals.

The new records indicate behavior that is much more varied and extreme than scientists expected for this species, says Simone Baumann-Pickering, a marine mammal biologist at the Scripps Institution of Oceanography in La Jolla, California. One exceptional whale dove to 9,816 feet (2,992 meters), while a second stayed down for 138 minutes.

Scientists and the U.S. Navy are especially interested in these whales because sonar activity has stranded individuals on beaches in the Mediterranean Sea, the Canary Islands, and the Bahamas, says Greg Schorr, a research biologist with the Cascadia Research Collective in Olympia, Washington. (See "U.S. Navy Wins Dispute Over Sonar, Whales.")

So far, no such strandings have occurred in southern California—the site of a Navy sonar testing area—he adds.

The new study, conducted in that testing area and published today in the journal PLOS ONE, is the first long-term look at the diving behavior of these animals.

View Images NG STAFF; EMILY M. ENG. SOURCES: PAUL J. PONGANIS, COMPREHENSIVE PHYSIOLOGY; GREGORY S. SCHORR, ET AL. PLOS ONE; SHINGO MINAMIKAWA, ET AL. FISHERIES OCEANOGRAPHY.

Out to Sea

Studying beaked whales is notoriously difficult, says Randall Davis, a marine mammal biologist at Texas A&M University in Galveston. They spend much of their time at depth far from shore, and they don't approach boats to ride the bow wave like dolphins do.

Some beaked whale species are known only from specimens that have washed up on shore, adds study co-author Schorr.

Cuvier's beaked whales may be the most well known of this mysterious group of marine mammals, says Davis, who was not involved in the study. Even so, researchers are just now getting a clearer picture of how these animals spend their days.

Schorr and his colleagues attached tracking tags to eight Cuvier's beaked whales off San Nicholas Island (map) in southern California and followed them for several months as the animals dove in search of food.

The scientists weren't expecting to see any of the whales dive to nearly 10,000 feet (about 3,000 meters). Schorr was so surprised at first that he thought the tag was malfunctioning. He tested an identical tag in a pressure chamber to make sure it could report correctly at such depths.

Champion Divers

It's a "spectacular" maximum dive depth, says Texas A&M's Davis. But going to such extremes in search of food—most likely deep-sea squid—must be worth the time and energy, he says. Otherwise the animals wouldn't do it.

Diving to depth can cause all kinds of problems, he says, including the collapse of air-filled spaces within the body, such as lungs. There's also the potential for a condition called high-pressure nervous syndrome, which can trigger convulsions. (See "How Diving Mammals Stay Underwater for So Long.")

Yet somehow marine mammals like Cuvier's beaked whales are able to dive repeatedly to thousands of feet without any apparent ill effects.

Marine mammals have rib cages that can fold down, collapsing the lungs and reducing air pockets, explains Davis. But exactly how Cuvier's beaked whales manage to avoid high-pressure nervous syndrome is still unknown.

That's one of many mysteries researchers would like to solve in the coming years, although Schorr and other researchers first want to concentrate on obtaining basic behavioral data.

Schorr is currently studying whether Cuvier's beaked whales display adverse or unusual behavior in response to sonar in southern California. "That's an advantage to these long-term studies," he says. "We can look at how long any impacts last and how long it takes [the whales] to get back to normal behavior."