Marine scientists and environmentalists have long shared concerns about the responsibility of U.S. Navy strategic sonar exercises in mass strandings of marine mammals. Finally, almost two years after a mysterious mass stranding of 16 whales and 1 dolphin in the Bahamas, the U.S. Navy has acknowledged the role of sonar tests in the tragic event. Earthwatch scientists Ken Balcomb and Diane Claridge, from the Center for Whale Research, were largely responsible for bringing the physical causes of the strandings to light.
On March 15 and 16, 2000, 14 beaked whales, 2 minke whales, and 1 spotted dolphin stranded in the Bahamas Islands, within hours of intensive Navy sonar exercises in the area. Although six of the whales and the dolphin died, ten whales were returned to the sea alive with the help of Balcomb and Claridge and their Earthwatch volunteers on Dolphins and Whales of Abaco Island.
"The participants were wonderful," said Balcomb. "That was the first day of a team and we were just briefing them that they couldn't expect a whale every day. And boom! There's one right on the beach in front of us. That was only the beginning."
In addition to assisting some of the whales back to sea, Balcomb and Claridge took tissue samples from the dead whales for further study. This included two heads of beaked whales, each weighing a couple hundred pounds, which were temporarily stored in the freezer of a local restaurant. Balcomb managed to transport the two heads up to Boston, where scientists at Harvard Medical School conducted a series of three-dimensional computerized tomography (CT) scans of them. The scans revealed trauma to the inner ear and part of the brain, establishing that the strandings were more than a matter of disorientation.
"There's actually hemorrhaging going on in these cases" said Balcomb. "The National Marine Fisheries Service says these injuries are survivable-and they are, but only with hospitalization. And whales don't have that option."
Balcomb describes how sonar and other loud sounds can result in damaging "resonance effects" in the air spaces of marine organisms, such as a whale's inner ears, damaging the sensitive tissues around them. A recent article in the Journal of Theoretical Biology supports this contention, describing how resonating gas bubbles in marine mammals may cause damage to surrounding tissues by growing, as they do in the serious divers' ailment known as "the bends."
A joint report issued by the Navy and the National Marine Fisheries Service in December confirms that the sonar exercises, combined with the oceanographic conditions and the underwater topography, led to the strandings. The report marks the first time sonar has been shown to cause fatal trauma in marine mammals, and demonstrates that future sonar tests will have to consider the protection of whales from its damaging effects as well. The Navy is planning new policies to prevent such injuries, and increasing funding of marine mammal research to $9 million in the coming year.
Earthwatch Institute is an international nonprofit organization which supports scientific field research worldwide by offering members of the public unique opportunities to work alongside leading field scientists and researchers. The Institute's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.