New whale-stranding suspect

Sonar: Scientists are looking at the acoustical ping-pings of Navy ships as a cause of marine mammals losing their way and dying.

Medicine & Science

October 11, 2004|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

It remains one of the great mysteries of marine science: Why do whales and other marine mammals strand themselves, swimming into shallow waters and washing ashore to die?

Decades of research show that many of the strandings are caused by age-old maritime hazards: collisions with ships, infections from parasites, starvation and old age.

But scientists have a new suspect these days: Navy sonar.

Whales, dolphins and other marine mammals use echolocation - a kind of natural sonar -to detect predators, hunt for food, find mates, keep track of offspring and orient themselves in a dark and murky world.

"These are acoustic animals, they use sound the way we use vision to orient ourselves and find their way," said Brandon Southall, an expert on marine mammal bioacoustics with the National Oceanic and Atmospheric Administration.

Some marine mammal experts say that Navy sonar, which generates intense sound waves that bounce off objects to reveal their location, confuses the animals and disrupts normal ability to navigate.

Sonar-related strandings are occurring more often as the Navy increases its use of sonar in coastal areas. Since the 1980s, it has caused the stranding of dozens of marine mammals, said the Natural Resources Defense Council (NRDC), a California environmental group.

Navy officials say that sonar - by itself - does not automatically cause whale strandings.

"The idea that there's a cause and effect relationship is tenuous at best," said Capt. Mark Boensel, director of environmental readiness for the Chief of Naval Operations.

Navy sonar isn't the only potential problem. Oil company geologists blast ocean beds with high powered air guns to find deep-sea oil deposits. About 80,000 commercial ships, fishing boats and other craft ply oceans every day, sending waves of sound into the depths.

"The oceans are extremely noisy places," said Mardi C. Hastings, a scientist in the Office of Naval Research. Hastings spoke last month at an NOAA-sponsored gathering on marine mammals and noise at the National Aquarium in Baltimore.

At Congress' urging, the U.S. Marine Mammal Commission has set up an advisory panel to find ways to reduce the impact of noise created by all three sources. The group is holding hearings and will issue a report in the spring.

Meanwhile, Navy sonar faces the most intense scrutiny. NRDC sued the Navy two years ago over a plan to use a new type of low-frequency sonar which, environmentalists claimed, would harm whales and other mammals. The group won a judgment that restricts sonar use to Asian waters. But now it's considering another suit over the Navy's more widely used, mid-frequency sonar, deployed in training exercises on 60 percent of the Navy's 300 vessels.

"We don't think that whales should have to die for what are essentially practice sessions," said Joel Reynolds, an NRDC lawyer.

Navy officials say close-in sonar training is critical to deal with a new generation of quieter, diesel-electric submarines, acquired by several foreign navies, that threaten coastal areas.

Navy officials acknowledge that given the right conditions - as occurred in the Bahamas in 2000 - sonar can kill whales. Seventeen, mostly rare beaked whales, stranded themselves over 150 miles of shoreline within 24 hours after a Navy exercise.

But in that case, an unusual mix of conditions, including sea-floor topography, ocean temperatures and salinity levels, combined with the sonar to cause the strandings, Boensel said.

After the Bahamas incident, Boensel said, the Navy stopped using sonar in the area and avoids waters with similar conditions. Navy officials say they also try to minimize damage by shutting down sonar within 500 yards of marine mammals, training lookouts to spot the animals at sea and holding exercises in waters where whales don't normally swim.

The Navy also spends $10 million a year to study the problem - 70 percent of all U.S. research on the subject. And it dispatches scientists tostrandings each time one is reported. "The U.S. Navy does not go out to sea with the intention of harming animals," Boensel said. "That's not what we're about."

Most of the strandings are confined to a species. "It's the beaked whales that seem to have some type of sensitivity to midrange sonar," said Frank Stone, the Navy's marine mammal program manager.

Exactly why is a mystery.

"We just don't have enough hard data on their physiology and behavior to do anything besides speculate," said James Mead of the Smithsonian Institution, a nationally known expert on beaked whales.

One reason so little is known is that the animals are so elusive - diving as deep as 4,000 feet.

In research near Italy this summer, scientists from the Woods Hole Oceanographic Institute tracked four beaked whales by attaching miniature acoustic recorders to their bodies. They discovered that the whales only begin to make the clicking sounds they use to locate prey at depths of about 650 feet.

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