Study links bends-like whale deaths to sonar
By Marc Kaufman
High-powered sonar from Navy ships appears to be giving whales and other marine mammals a version of the bends, causing them to develop dangerous gas bubbles in some vital organs and blood vessels, to beach themselves and die, according to a study published today in the journal Nature.
Associated Press library photo Sept. 9, 2002
Fourteen beaked whales beached themselves in the Canary Islands during naval exercises last year.
Associated Press library photo Sept. 9, 2002
The new data begins to explain how and why high decibel mid-frequency sonar used by the U.S. Navy and other military fleets appears to cause some deep-diving marine mammals to die. Although the bends was previously unheard of in whales, dolphins and porpoises, the British and Spanish researchers concluded that nitrogen bubbles in the whales' tissue was "the most likely cause" of the Canary Island strandings.
"This is the best data we've ever seen from a sonar-related stranding," said Roger Gentry, coordinator of the U.S. government's National Oceanic and Atmospheric Administration Fisheries Acoustics Team. He said that NOAA will hold a workshop with the authors and others in the field later this year to assess the new information and try to reach some scientific conclusions.
The new research from the Canary Islands suggests two possible ways in which the whales could be harmed by the gas bubbles. One is similar to how humans get the bends: that the whales panic at the sound of the loud sonar noises and rise too quickly from deep water. As they rise, nitrogen bubbles can be formed from the rapid change in pressure and cause the bends.
The other hypothesis involves bubble formation caused directly by the sonar on gas nuclei, or bubble "precursors," in whale tissues already highly saturated with nitrogen.
Gentry said that the scientific community, at this point, remains skeptical that rapid ascents are causing the bubble-formation. "From an evolutionary point of view, it does not seem likely," he said. "Whales have been diving like this forever, and should have evolved mechanisms so they wouldn't succumb to decompression."
The Canary Island strandings and research involve mid-frequency (or pitch) sonar coming from Spanish-led, international naval maneuver. But they could have impact on a contentious debate now going on over the U.S. Navy's desire to deploy very loud low-frequency sonar around the world to detect "quiet" submarines. That effort was stopped by a federal magistrate in California in August, who said the government had violated several environmental laws in giving the Navy permission to deploy the new sonar globally.
"We know there is a connection between military sonar and strandings, and now we're making progress on the physical mechanism causing them," said Joel Reynolds, an attorney with the National Resources Defense Council, which sued the government over the low-frequency sonar. "This is very compelling scientific evidence."
Navy spokesman Lt. Cmdr. Cappy Surette said that officials are still studying the Nature article. But he said the Navy already takes many steps to avoid harming sea creatures and that the new sonar technology is necessary.
"Submarines are becoming an increasingly serious threat to the U.S. Navy," he said. "Diesel submarines have become increasingly difficult to detect and are proliferating around the world."
He also said "there is no evidence of any negative impact on marine mammals" in areas where the new low-frequency sonar has been tested.
The legal problems faced by the new Navy sonar system, called the Surveillance Towed Array Sensor System-Low Frequency Active, have upset some in Congress and helped spur successful efforts to pass legislation to limit the reach of various environmental laws that effect the Defense Department. That legislation, which is part of the Defense Department appropriations bill, is now in conference. The House language broadly exempts the Defense Department from provisions of the Endangered Species Act and the Marine Mammal Protection Act, while the Senate language is considerably less limiting.
There have been several mass beachings of whales and dolphins tied to high-decibel sonar since the phenomenon was first identified in 1996, and Navy researchers are now going back to see if other strandings can be connected with nearby Navy sonar use.
Whales and other marine mammals are highly sensitive to sound and use it to communicate. Different species hear at different frequencies, and so are affected by different kinds of sonar. The low-frequency sonar that the Navy now wants to use around the globe operates at the sound level used by the largest, and some of the most endangered, whales.
The whales stranded in the Canary Islands are beaked whales, the same kind as those killed in a similar stranding in the Bahamas in 2000. Beaked whales are relatively small whales that dive deeper than most to feed on squid.
The Navy initially said that its sonar had no connection with the 2000 stranding, but a later inquiry ruled out all other possibilities and concluded the sonar most likely caused the animals to die.
Several of the Bahamas whales also were studied by scientists, who found large internal hemorrhages around the animal's ears. The gas bubbles found in the Canaries whales were not detected in the Bahamas whales, but Gentry of NOAA said that is most likely because it took longer there to get the dead animals frozen to stop decomposition.