A new study recently published in the journal Respiratory Physiology and Neurobiology offers evidence to support the theory that beaked whales get the bends when they surface rapidly, possibly after being startled by naval sonar. This could help understand why beaked whales appear to be more vulnerable to the potentially harmful effects of sonar than other marine mammals.

Together with other studies, the results may also help scientists and regulators think of how navies could adjust their sonar use during training to prevent beaked whale strandings and deaths. The study used data gathered from three species in the beaked whale family. Two of the species, Cuvier's and Blainville's, were observed in Hawaii waters. The third, northern bottlenose whales, were studied off Nova Scotia, Canada. In 2000, several beaked whales washed ashore with bleeding around their brains and ears during Navy exercises in the Bahamas. The bleeding may have been caused by bubbles that formed in the whales' bloodstreams when they surfaced more quickly than normal. There have been other similar mass strandings that happened at the same time as naval sonar exercises which include Greece (1996), the Bahamas (2000) and the Canary Islands (2002).

The US Navy is pushing for more research in the area, budgeting millions of dollars over the next five years to understand how marine mammals hear and how sound affects them. The new beaked whale study was funded in part by the Office of Naval Research. Beaked whales are among the least studied marine mammals because their populations are small and they spend most of their time deep below the surface,little is known about how the whales react to underwater sounds. The study so far concludes the animals are at higher risk of suffering the bends because they live with extremely high levels of nitrogen in their blood and body tissues. Nitrogen builds in mammals, including humans, when they dive. Beaked whales likely accumulate such high levels of nitrogen because they repeatedly dive to great depths sometimes, almost 5,000 feet below the surface for long periods, sometimes to over an hour. When the marine mammals ascend slowly, the nitrogen in their blood stays dissolved but when they surface too quickly, the nitrogen comes out in bubbles. This is what gives them a form of decompression sickness, or the bends, a condition also known to scuba divers.

Scientists now need to study what sound levels and frequencies may be prompting beaked whales to react in such a way that's clearly dangerous for them. Some scientists have been conducting tests on beaked whales in the Bahamas since 2007, but the results have not yet been published. Currently, nothing is known about the population trends of the worlds' 21 beaked whale species, regardless of where they are in the world. Therefore it's difficult to measure how sonar use may be affecting them. There are only 56 Cuvier's beaked whales and about 140 Blainville's beaked whales in waters off the Big Island of Hawaii.

The latest study is titled "Could beaked whales get the bends? Effect of diving behavior and physiology on modelled gas exchange for three species: Ziphius cavirostris, Mesoplodon densirostris and Hyperoodon ampullatus.