In 1996, 12 Cuvier's beaked whales became stranded on the west coast of Greece. Three years later, four beaked whales stranded themselves in the U.S. Virgin Islands. The following year, there were three beaked whale strandings on Madeira. Then, in 2002, 14 different whales from three different species became stranded in the Canary Islands.
There wasn't anything inherently unusual about these series of strandings; for reasons that remain unclear, many species of whales will, on occasion, beach themselves. However, each of these specific occasions - and several other subsequent occasions – had one factor in common: Military activity was taking place in the area, in which either U.S. Navy or NATO vessels were testing mid-frequency or low-frequency active sonar. Given the extreme importance of sound to many cetaceans, researchers speculated that the noise from the sonar may have been directly or indirectly responsible; the Natural Resources Defense Council (NRDC) noted that:
Many of these beached whales have suffered physical trauma, including bleeding around the brain, ears and other tissues and large bubbles in their organs. These symptoms are akin to a severe case of "the bends" - the illness that can kill scuba divers who surface quickly from deep water. Scientists believe that the mid-frequency sonar blasts may drive certain whales to change their dive patterns in ways their bodies cannot handle, causing debilitating and even fatal injuries.
In 2005, NRDC filed a lawsuit contending that the use of active, submarine-hunting sonar posed threats to cetaceans and violated, among other laws, the Marine Mammal Protection Act, the National Environmental Policy Act and the Endangered Species Act. Although a Los Angeles federal court agreed, and ordered the Navy to enact a number of safety measures to protect whales, Navy officials appealed to the Supreme Court, which in 2008 overturned two of six mitigation measures while leaving the rest in place.
Meanwhile, research into the impact of active sonar on cetaceans continues – including, to its credit, by the Navy. Indeed, the Navy participated in new research that has provided the first concrete evidence that sonar does indeed affect behavior in at least one cetacean species.
Writing in the online journal PLoS One, Peter Tyack of the Woods Hole Oceanographic Institution and colleagues describe a study at the Atlantic Undersea Test and Evaluation Center in the Bahamas, in which they deployed underwater microphones to listen for the "click trains" emitted by Blainville's beaked whales using echolocation to find their prey:
Initially, some two dozen whales were foraging on the Navy's test range, according to the clicks. But as the sonar exercises began, the clicks started to disappear, suggesting that the whales cut short their hunting and swam kilometers away from the sound. Once the exercise stopped, the whales returned to the range within a few days, probably because the range is a prime feeding ground.
"It was clear that these whales moved quickly out of the way," said Ian Boyd of St. Andrews University in Scotland, one of the paper's co-authors. "We now think that, in some unusual circumstances, they are just unable to get out of the way and this ends up with the animals stranding and dying."
Photograph: The satellite tag on this male Blainville's beaked whale records the whale's response to naval sonar and other recordings. U.S. Navy photo by Ari S. Friedlaender.