for National Geographic News
Undersea noise from naval exercises appears to give beaked whales the bends, an ailment most commonly associated with scuba divers who rise to the ocean surface too quickly, according to a new study.
The finding comes from autopsies performed on beaked whales that stranded themselves on beaches in the Canary Islands four hours after military sonar activities commenced there September 24, 2002. The research is reported in the October 9 issue of Nature.
Scientists for years have suspected a link between sonar activities and mass strandings of marine mammals—similar events have occurred recently in the Bahamas and Greece—but they are uncertain as to why sonar causes the animals to strand themselves.
The new research is based on autopsies performed by scientists with the Institute for Animal Health at the University of Las Palmas de Gran Canaria in Spain shortly after the beaked whales stranded themselves on the beaches of Fuerteventura and Lanzarote.
The researchers cut into and examined eight Cuvier's beaked whales (Ziphius cavirostris), a Blainville's beaked whale (Mesoplodon densirostris), and a Gervais' beaked whale (Mesoplodon europaeus). They found gas bubbles in blood vessels and hemorrhaged vital organs.
"We think the animals arrived at the coast after the beginning of the exercises in an injured state due to a disseminated microvascular hemorrhage in vital organs, associated with a systemic embolism," said Antonio Fernández, one of the Spanish researchers. "After beaching, their situation was worse due to the well-known stress stranding syndrome that did more severity to the lesions, resulting in cardiovascular collapse and death."
Roger Gentry, a scientist with the National Marine Fisheries Service in Silver Spring, Maryland, who studies marine mammal strandings, said the connection between the beaked whale strandings and the military sonar exercises is clear, but he is not certain the sonar causes an ailment similar to decompression sickness, as reported in Nature.
"None of the authors is an expert on decompression sickness and none of the results have been seen by anyone who is an expert on decompression sickness," he said.
The fisheries service is trying to set up a workshop before the end of year where the authors of the Nature paper can present their findings to experts on decompression sickness. Similar research was presented at a workshop organized by the fisheries service in 2002 and it remains a valid hypothesis, said Gentry.
Sonar and Whales
Sonar technology, such as that used during the Cold War, was passive: essentially big microphones that listened for the distinctive sounds emitted by large submarines.
The U.S. Navy and other militaries around the world have since deployed mid-frequency active sonar designed to find a new generation of smaller, stealthy submarines by sending out sound waves and listening for the reflections off objects, thus giving away their location.
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