Home videotape recorded the high-pitched sound. It's what an underwater microphone picked up when the USS Shoup tested its sonar in Puget Sound in May. That ear-splitting sound is sending shock waves through the world of marine mammal advocates.

Dead harbor porpoises may be the result of the testing. "I'm convinced it's having an effect on their behavior at the very least," says whale researcher Ken Balcomb. He videotaped the sonar tests May 5 and says, "I believe it's also injuring and killing some."

Sonar's effect on marine mammals has been a battle between the Navy and researchers since seven whales died in the Bahamas three years ago.

What happened in the Sound may help resolve that. Because for the first time ever, there is a wealth of evidence surrounding the incident. Video caught what the sonar testing in May did to killer whales. And around the same time, the carcasses of the 11 porpoises washed ashore, and were quickly recovered and frozen.

Now examinations, including CT scans, and necropsies, should answer the questions: Did the sonar hurt the porpoises? Did it kill them?

"These dolphins, not only these but other animals that washed up on beaches, are a window to what's going on in nature," says Dr. Pete Schroeder. The Navy hired the marine mammal veterinarian to keep tabs on the exams for them.

Whale researcher Ken Balcomb is also watching closely. "It's extremely important for our government to know if one of our weapons systems or defense systems is destroying our environment... If we're inadvertently killing them, we've got to find out."

NOAA fisheries expects to have the results of these tests back in two to three months and then the real battle begins. Because if sonar is found to be responsible for these deaths, the question becomes what does the Navy, what does the government do about it?

The Navy says that until the examinations are complete there's no way to know what killed the porpoises.

The Navy says it is conducting its own investigation on the use of sonar and its effects on all marine mammals in Puget Sound.