"We definitely showed that there are physiological and some behavioral effects [from repeated, loud sonar], but to extrapolate that into the wild, we don't really know," Mooney said. "The sound levels that we used were essentially the equivalent of if an animal is about 40 metres (yards) from the sonar source," he said. "The animal would have to be there for about two minutes or so" to get the same level of exposure as in the Hawaii experiment. "That's a pretty long time for an animal to be there. If the sound's pretty loud and the animal's not used to it, he would move around, and the ship itself is moving in a different direction." On the other hand, a cetacean that sought to escape a persistent loud sonar may not easily find an escape route, said Mooney. "In the ocean, sound doesn't attenuate in a normal fashion. Sound can sometimes get trapped at the surface, in layers called thermoclines, at the top 325 feet or so. "Maybe in those conditions it's more difficult to get away from the sound to a quieter area." Further work is needed to figure out what happens at lower sound levels from sonar and at greater distances to see how cetaceans respond, he said. Related Links: Go to Discovery Earth for slide shows, quizzes, interviews and more. |
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