KEY WEST, Fla. -- The U.S. Navy and marine wildlife experts are checking if the use of sonar on a submarine off the Florida Keys triggered the beaching of about 70 dolphins.

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Slideshow: Dolphins Beach Themselves Off Marathon Key
Video: Dolphins Beached Off Florida Keys

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The Navy won't say if sonar was used during a training exercise involving the USS "Philadelphia," which is based in Connecticut. The dolphins started beaching themselves on flats and sand bars about a quarter–mile from Marathon, Fla., and in a nearby channel, the day after the exercise. More than 20 have died.

Some scientists say that loud bursts of sonar, which can be heard for miles in the water, may disorient or scare marine mammals. They say it could cause them to surface too quickly and suffer the equivalent of what divers know as the bends – when sudden decompression forms nitrogen bubbles in tissue.

Members of a marine-mammal stranding network have been caring for the dolphins.

"They are definitely under stress," said Sarah Gomez, of NOAA Fisheries. "These are aquatic animals and being on land is the last place they want to be."

"Our basic goal is to stay in the water with them and keep their blowholes above water so they can breathe," Kate Fisher, one of the volunteers who worked all night to help rescue the dolphins.

"This is my fourth rescue," Fisher said. "They don't know us. These are wild dolphins and we're alien to them. But when you're in the water with them, you get the sense that they understand that you're not trying to hurt them. For the most part they're calm. They read you. They're very smart animals and they can feel your heartbeat. So when you're next to them it's a very calming experience."

As for the volunteers, they're feeling the stress, too. "It's chilly but you get used to it," Fisher said. "You get cold, but it's worth it."