The Not-So-Silent World
By Jean-Michel Cousteau
We divers know that the sea is a noisy place, full of noisy animals. On coral reefs, we are accustomed to the sounds of parrotfish chomping corals. In the shallow Caribbean we enjoy the clicks and whistles of dolphins. And in the waters off Hawaii, we thrill to the complex songs of humpback whales. Noise is part of what makes the sea and its animal inhabitants so intriguing. But a recent report by the Natural Resources Defense Council suggests that this universe is at risk, and the culprit is us. The report, "Sounding The Depths," claims that human-generated undersea noise pollution is more than an occasional annoyance-it's a frontal assault on oceanic health.
Consider the sources: commercial shipping, fishing, oil exploration, and military and scientific research. Ships are bigger, more numerous and louder than ever before. Supertankers produce an overwhelming sheet of white noise, caused by cavitation, the bursting of water bubbles around the propellers. Fishermen rely on pinging devices to scare off dolphins. Pingers save the dolphins from becoming bycatch, but they also deny them access to feeding grounds. Oil exploration involves the use of air guns to send charges through the ocean floor while the military is testing the next generation of low-frequency active sonar (LFA), which uses high-volume low-frequency sound waves to locate submarines. And scientists aren't far behind: a new project called Acoustic Thermometry of Ocean Climate (ATOC) relies on pulses of low frequency sound waves to gauge water temperature and chart the progress of global warming. These pulses are audible some 11,000 miles from their source.
It's hard to determine how all this noise affects wildlife, but a growing body of evidence suggests that it is a serious problem. Many species-especially marine mammals-depend on sound for survival. Whether serenading a prospective mate, navigating or hunting by sonar, avoiding predators, or keeping their young close on a long migration, marine mammals experience their world through sound, not sight.
Whales, dolphins and pinnipeds routinely suffer death, hearing loss, and disorientation from massive human-induced sonic events. But the real danger may be the constant rise of background noise-over 10 decibels, or one order of magnitude, between 1950 and 1975. Even at lower volumes, noise can make whales alter migration routes, strand, or cease their own vocalizations. Dolphins and sea lions become stressed and disoriented by noise. The swim bladders of fish can burst.
The numbers are startling. Ship propellers produce noise in the 170-190 decibel range. ATOC rumbles in at 195. Active sonar at 230. Air guns at 250. When you consider that sea lions suffer hearing loss around 140 decibels and that gray and bowhead whales have been observed to alter their migration routes to avoid 120-decibel noises, you begin to understand the magnitude of the problem. The Council's report notes: "For a marine mammal, each additional decibel can mean the loss of vital information: the call of a calf, of a predator, or of a prospective mate."
Unless some kind of action is taken, this problem will only worsen in the years to come. The human population will approach 9 billion by the year 2050. More than one-third of those people will live within 50 miles of the sea, drastically increasing our impact on the coastal zone. With fewer fish to catch, fishing may become more intense, and pingers more popular. Commercial shipping will increase as the economy becomes more global. As for active sonar, it is hard to imagine the U.S. will always have the monopoly. If it is successful, it surely will be imitated. The ocean could become the world's sonar circuit board.
Just as there is no refuge from pollution, there should be no refuge from responsibility. The NRDC is calling upon the International Maritime Organization, the World Trade Organization and the United Nations to develop global noise reduction guidelines, and these guidelines must apply to all.
Some will say that nothing should be done, that "the science isn't in yet." True, undersea acoustical research is incomplete, but there is enough evidence of a crisis to justify limits at least on new sources of noise while scientists race to supply more complete data. In the meantime, it may behoove policy makers to err on the side of caution.
Finally, one might ask: why should divers care? Well, one of the Navy's tests involved the impact of LFA on humans. Divers subjected to the sonar's 160-decibel bursts suffered vertigo, motion sickness and chest pains. One test diver developed chronic mental dysfunction and seizures. It's truly one ocean, and what affects marine life affects us as well.