In a landmark study, the U.S. Navy has concluded that it killed at least six whales in an accident involving common ship-based sonars. The finding, announced late last month by the Navy and the U.S. National Marine Fisheries Service (NMFS), may complicate Navy plans to field a powerful new sonar system designed to detect enemy submarines at long distances.
For decades, marine mammal scientists have suspected that sonar pings produced by military ships may have played a role in a half-dozen unusual strandings of beaked whales, toothy marine mammals that often feed deep in the ocean. In each case, researchers discovered the beached whales shortly after nearby military sonar exercises, but the remains were always too decayed to reveal evidence of sound-energy injuries.
On 15 March 2000, however, independent marine mammal researchers Ken Balcomb and Diane Claridge woke up to find a beached beaked whale outside their seaside home on Abaco Island in the Bahamas (Science, 26 January 2001, p. 576). They soon counted 17 other stranded marine mammals in nearby waters, some with apparently bleeding ears. They managed to collect tissue samples--including whole heads--from six of the animals that had died. Government scientists launched an investigation after learning that the strandings had occurred within 24 hours of a nearby Navy training mission.
In an interim report released 20 December 2001, Navy and NMFS scientists conclude that the strandings were caused by an "unusual combination" of factors, including sea-bottom contours and water conditions that may have channeled and magnified sonar pings. While the researchers could not pinpoint exactly how the sound energy injured the whales' ears or tissues, the acoustic assault appears to have left some dazed and confused, causing them to swim ashore or become vulnerable to shark attack. The Navy says that, in the future, it will try to avoid using sonar in similar situations during training runs, and it hopes to fund more research.
The study's result "doesn't surprise" Naomi Rose, a marine mammal expert with the Humane Society of the United States in Gaithersburg, Maryland. "There is no way the Navy could have avoided owning up," she says. But she believes the report is "carefully worded" so that it does not give ammunition to critics of SURTASS LFA, the new, lower frequency sonar system the Navy plans to deploy. NMFS is expected to announce soon whether it will give the Navy a permit to operate that system, but some environmental groups have threatened to sue to block the sonar's deployment.