deep diver.
violations of beaked whales off the coast of Italy Cuvier.
Natacha Aguilar Soto / University of La Laguna, Spain
Cuvier's beaked whale is a master of the ocean crushing depths. It can dive as deep as 2 km in search of prey, the deepest known for any mammal. Thus, scientists have been at a loss to explain why, in response to naval sonar tests, this champion cetacean sometimes succumbs to the same decompression sickness that afflicts divers. A new mathematical model suggests that, by reproducing the sounds of a predator, sonar strength whale to adopt a risky dive model.
Researchers have suspected a link between sonar tests and whales of death for nearly 20 years. In 00, the US Navy said its sonar exercises have led six beaked whales to beach fatally themselves in the Bahamas, and beached whales have died near the sonar-testing sites in at least five cases since . It was not clear how the sonar disorients animals and causes of these strandings, but some marine biologists suspect that the intense sound waves forcing the whales to get to the surface, and they have found evidence that tiny bubbles nitrogen develop in the whales' tissues and damage vital organs ( science NOW, October 9, 03). The same thing occurs when divers surface too quickly - a condition known as the bends. But a whale holds its breath during the dive, thus preventing the accumulation of nitrogen, so that theory does not seem to hold water. A group led by marine biologist Peter Tyack of Woods Hole Oceanographic Institution in Massachusetts suspected that whales alter their diving behavior in another way.
dives shallowThe whales are repeatedly trying to escape predators. The team wonders if such behavior could be risky, especially because the naval sonar - which is similar to the frequency of calls of the most feared opponent of the beaked whale, killer - could be forced whales to adopt a similar model dive. Thus, researchers analyzed mathematically diving behavior in Cuvier's beaked whales and dolphins to test whether nitrogen bubbles may develop in the tissues of whales during some repeated deep dives. The team consists of known physiological data in a model that maps how the bubble size could increase in the circulatory system, brain, muscle and fat tissue when a whale dives repeatedly at between 30 and 80 meters as long as 3 hours.
During normal diving behavior, scientists believe, the lungs collapse of marine mammals when they dive past 72 meters. This "intelligent mechanism," said Tyack prevents nitrogen to infiltrate the bloodstream. The team's model predicts that if the whale lungs do not collapse during a long series of shallow dives, pressure increased can cause nitrogen bubbles diffuse into the tissue, which increases the risk of bubble formation on the rise. the limitation of the duration of the sonar tests can prevent animals from diving in these harmful model, the team concludes in the current issue of Marine Mammal Science .
Noting that the diving behavior is extraordinarily difficult to study live animals, marine biologist Terrie Williams of the University of California , Santa Cruz, called the "extremely useful" model as new research supports gaps in model assumptions -. with actual observations to corroborate avoidance behavior, for example - scientists can try to home in length and the level of safe sonar exercises, clarifying the murky waters surrounding this debate. "Now it's a matter of how quickly [decompression sickness] happens," she said.
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