Thursday, October 09, 2003
Naval Sonar Causing "The Bends" in Cetaceans?
Sonar may cause a type of decompression sickness in whales and dolphins similar to the "bends" in humans, scientists said Wednesday. Although it seems an unlikely illness for the aquatic creatures, researchers from the Zoological Society of London and the University of Las Palmas in the Canary Islands have found bubbles in the tissue of stranded whales and dolphins similar to the effects of decompression sickness (DCS) in humans.
"The only way we can explain these findings is that it is a condition very similar to decompression sickness in humans," said Dr. Paul Jepson, co-ordinator of the U.K. Marine Mammal Stranding Project which contributed to the research. "Sonar may cause a disease like the bends," he said, adding that more research was needed to confirm the results. The finding, reported in the science journal Nature, is the first evidence of a bendslike illness in the creatures.
Scientists suspect sonar signals disorientate the animals, forcing them to come up to the surface too quickly, which could cause the creation of damaging nitrogen bubbles in their tissue. Both low- and mid-frequency sonar have been linked to whale strandings.
"It is widely accepted that there is a link between naval sonar use and mass strandings, predominately of big whales. What hasn't been fully understood is what the mechanism would be," Jepson added.
Autopsies by Spanish scientists on 10 of 14 beaked whales stranded in the Canary Islands after a multinational military exercise last year also showed evidence of DCS in the animals. The creatures started to appear on the beaches about four hours after the start of the mid-frequency sonar activity.
"Beaked whales have the highest levels of nitrogen in their tissues normally because they dive so deep, and that would be consistent with why it is the beaked whales that are most severely affected by sonar exercises," Jepson said.
Military sonar blasts areas of ocean with sound waves to detect submarines. Environmentalists say it produces noise levels that may harm marine mammals or alter their migration.
A mass stranding of whales in the Bahamas in 2000 has also been linked to a sonar system.
"The detailed examination of the mass stranded whales in the Canaries in 2002 suggests the naval sonar could induce a condition similar to DCS," Professor Antonio Fernandez of the University of Las Palmas said in a statement.
DCS is caused by a rapid decrease in pressure of either air or water, usually affecting scuba and deep-sea divers. If the transition between the pressures occurs too quickly, nitrogen bubbles form in the blood and tissue. "This new evidence from our study of marine mammal diseases in the U.K. challenges the widely held notion that cetaceans (marine mammals) cannot suffer from decompression sickness," Jepson added.