Blue Whale Requiem

ON SEPTEMBER 11, as pod after pod of massive endangered blue whales migrated through Southern California’s waters, lingering in unusual numbers off the coast near Orange County, the U.S. Navy resumed its tests of midrange sonar near San Clemente Island, the southernmost of the eight islands in the Santa Barbara Channel.

That very day, as if on cue, it happened: A blue whale was found dead near San Miguel Island, the northernmost island in the channel. Less than a week later, another turned up in Long Beach Harbor, 55 nautical miles from the naval base, and was towed out to sea by the Coast Guard. And then less than a week later a third, like the others, floating dead in the channel.

None of the whales seemed to have been killed by sonar. Scientists who examined two of them found no blood in their ear canals, nor hemorrhaging in their brains, as was the case with seven whales that became stranded and died in the Bahamas after Navy midrange sonar testing in 2000. The blue whales did not come ashore in groups, like 37 pilot whales that beached in North Carolina after midrange sonar testing there. Nor did anyone find gas bubbles in the blue whales’ tissue, which could indicate they had surfaced too quickly out of fear, then died from the bends. All the blue whales died with broken bones and blunt-force injuries, meaning they died because they were hit by ships.

But how does a blue whale — a mammal whose powers of echolocation allow it to accurately map an ocean — get struck by a ship whose propeller is so loud, says marine mammal expert Marsha Green, “you can hear it underwater when it’s still three days away”?

“The first easy answer is ‘we don’t know,’?” says Frances Gulland, director of veterinary science at the Marine Mammal Center in Sausalito, who attended the necropsies of the blue whales. “We know they were struck by ships, but whether they were disoriented first we have no way of telling — the organs were not fresh enough to determine that.”

Some researchers suspect the whales were poisoned by domic acid, a biotoxin produced by algae that has caused disorientation in smaller marine mammals. “We don’t know what it does to large whales yet,” says Gulland, “but we’ve taken samples from the whales’ tissue to find out.”

And then there’s the Navy’s sonar exercises, which a federal court had banned on August 6 pending an appeal by the Navy, only to have another federal court determine three weeks later that the sonar training could go forward.

Says Green, president of the Ocean Mammal Institute and an expert on noise in the ocean, “If the Navy was using sonar around the time that the whales were found dead, there’s no way you can ever say they weren’t affected by it.”

You can, however, say they might have been: Midrange sonar has killed before, and not even the top scientists understand exactly why. In this case, sonar might have ruined the whales’ hearing, and “we know that whales that are deaf are most likely to be hit by ships,” Green says.

Or sonar could have caused them to become temporarily disoriented, and made them more vulnerable to obstacles. Or naval sonar noise and noise from the very ship that struck the whale could have combined to trip up the cetacean’s keenest sense — hearing. “Container ships are so loud that you can hear one of them approaching a port three days before you get there,” says Green. “It’s the main source of noise in the ocean.”

This all points to one of the few facts marine biologists, experts in underwater acoustics and people like Green know for sure: The modern ocean is a mighty noisy place. In a study published last summer, John Hildebrand and Sean Wiggins of the Scripps Institution of Oceanography at UC San Diego compared ocean sound data from the ’60s to the present and found that ocean noise — from ships, the seismic surveys conducted by oil companies, and sonar — has increased tenfold in 40 years.

And to a mammal that lives in the ocean — an animal with an acoustic memory 10 times that of humans, for whom sound is a navigational tool more accurate than the sight of any creature on Earth — a noisy ocean is a dangerous place indeed.

Humans measure sound in volume and frequency. We rate the volume level in decibels, and agree that at 100 decibels we begin to feel discomfort in our eardrums. At 160 decibels our eardrums rupture, ruined for good. We measure the frequency in hertz — another way of saying “per second.” We cannot hear sounds below 20 vibrations per second, or 20 hertz, and, once past age 30, we can’t hear anything higher than 18 kilohertz — 18,000 vibrations per second.

In January 1999, the U.S. Navy released a document detailing the potential environmental impact of a different kind of sonar — low-frequency active sonar, or LFA. It described a perverse sort of experiment in which a 32-year-old Navy diver was exposed underwater to LFA at 160 decibels — because of the muting effect of water, the above-ground equivalent of 100 decibels. It took 12 minutes for the diver to succumb to dizziness and drowsiness, after which he was pulled from the water. Later he had a seizure and temporarily lost his memory.