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.

But two years after the experiment, the the report says, the anonymous diver still takes antiseizure medication for his acquired condition, as well as antidepressants.

The Natural Resources Defense Council got a permanent injunction against what it calls “unbelievably loud” LFA sonar in 2003. But at 235 decibels, midrange sonar, useful in rooting out “silent” submarines that may prowl the seas — is much louder than what disabled the Navy diver. How exactly it would affect a blue whale — or the grays that migrate south along our coasts later in the year and return north to Alaskan waters each spring — is a mystery. Of the 83 species of whale known to roam the ocean, scientists know the hearing range of only 11.

“With the big baleen whales, we don’t really know which frequencies they can hear,” not to mention physically withstand, says Dave Mellinger, an expert in marine acoustics at Oregon State University. “You can’t catch one and put it in a tank and test its hearing.” But “we assume they can hear [up to] a few kilohertz frequency.” The calls of blue whales in the Atlantic Ocean speak in “a different dialect” from Pacific blues, but both are below human hearing range.

“I remember hearing a blue whale for the first time,” says Mellinger, who has often submerged microphones into the ocean. “It’s a very low pulsing sound. They really sound impressively big.”

It has been said that a blue whale in the middle of the ocean can build in its mind’s eye a picture of the entire ocean, simply by sending out that sound and registering the echo. But what happens when the echo comes back muddied by a flood of noise?

“That’s an open question,” Mellinger says. “It could be akin to looking into a fog — the noise obscures things at great distances. We don’t know what effect it has on their migrations or ability to find mates.”

In fact, only in the early 1990s did anyone make a connection between human-generated sound and marine mammal strandings, even though such strandings have occurred since 1963, when Cuvier’s beaked whales, a smaller species, washed up on the shores of Sagami Bay, Japan, after U.S. naval maneuvers there.

According to a California Coastal Commission report in 2005 on the environmental impact of marine noise, that 40-year period of ignorance “underscores how easy it is to miss the connections between noise and a variety of impacts on marine mammals.” It also underscores one of the report’s key points: Humans know so little about marine mammal hearing that they would be wise to err on the side of caution.

In early November, the 9th Circuit Court of Appeals will convene to decide whether to continue to allow the Navy’s midrange sonar testing. Joel Reynolds, an attorney for the NRDC, one of the groups suing the Navy, is optimistic that the tests will be halted. The Navy itself estimated the exercises would cause permanent injury or death to 170,000 marine mammals and 4,000 beaked whales — violating California’s coastal-protection laws.

“I just have to shake my head over why it is that these remarkable creatures have to be subjected to this kind of treatment,” Reynolds says. “This is an amazing coast that we have, with a spectacular abundance of species. It’s a very odd place for the Navy to be using as a training area.”

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