NEW YORK (Oct. 10, 2003) -- Scientists have long suspected a link between mass whale strandings and the military's use of powerful sonar systems, but the evidence - dying whales washing ashore when sonar exercises occur - has been mostly anecdotal. Now, international researchers have identified a disorder similar to decompression sickness, or the bends, as the cause of at least some whale beachings, and they say military sonar is most likely to blame. The new findings, reported Thursday in Nature, are based primarily on necropsies of 10 whales that stranded themselves in the Canary Islands during a 2002 international naval exercise there that included one American ship. The incident drew worldwide attention, and this year environmentalists in California sued to stop the U.S. Navy from developing a newer, more far-reaching sonar system. All of the Canary whales examined had widespread bubble formation in tissue and blood vessels, the study says. The same thing occurs in scuba divers who surface too quickly after a deep dive. "The bubbles forming in these animals may not be immediately fatal," said Paul Jepson, a lead author of the study and a researcher at the Zoological Society of London. "But it does make them distressed or causes impairment, and it's quite logical to conclude that this is what leads them to strand." The study challenges the conventional notion that marine mammals cannot suffer from decompression sickness. But more important, says Jean-Michel Cousteau, director of the Ocean Futures Society in California, it demonstrates the toll that underwater noise pollution can have on marine life. The U.S. Navy, stressing that it uses highly trained lookouts and other methods to protect whales, is reluctant to accept the study's conclusions. "Previous studies have not, to date, revealed evidence of decompression sickness as suggested by the article," Lieutenant Commander Cappy Surette, a navy spokesman, said in an e-mail message. "The National Oceanic and Atmospheric Administration and the U.S. Navy were not invited to participate in the studies conducted of these beaked whales and, as a result, we are unable to determine the actual cause of the strandings." | | It is widely known that breathing compressed air from a scuba tank even at the depths that recreational divers frequent causes gases like nitrogen to dissolve and build up in the blood and tissues. If divers have been too deep, or down too long and ascend too quickly, the accumulated nitrogen can turn to bubbles as the pressure decreases. The bubbles block blood flow and cause tissue damage, which, when severe enough can be fatal. Even though the bends are thought of as an ailment of scuba divers, there have been reports of something like decompression sickness, called taravana syndrome, in people in Polynesia who accumulate high levels of nitrogen while making repeated free-dives without compressed air. How the bends would occur in whales and other marine mammals which commonly dive to great depths is not completely understood, Jepson said. What is known is that the beaked whale and the dolphin species that strand themselves most often when sonar is used nearby are deep divers that tend to have enormous levels of nitrogen in their tissues. One theory holds that military sonar, in some cases at decibels similar to a rocket launching, can lead to bubble formation by startling the animals into shooting too rapidly from deep to shallow waters. Another suggests that the acoustic signals may somehow directly set off bubble eruptions in the nitrogen saturated tissues. The mid-frequency sonar system that stranded the whales in the Canaries has also been blamed by environmentalists for mass whale deaths in the Bahamas in 2000 and in at least three other incidents in the Canaries in the past 20 years. The navy is replacing that system, which is used by a number of other countries for detecting submarines, with a newer generation of long-range, low frequency sonar called the Surveillance Towed Array Sensor System, or Surtass LFA, that can sweep 80 percent of the world's oceans. In the late 1990's, the navy spent two years and $10 million studying the impact low frequency sonar might have on marine mammals, Surette said, and found its effects negligible. Environmental groups like the National Resources Defense Council dispute the findings. |
