“Sonic Sea,” which will air Thursday on Discovery Channel, will take you down beneath the ocean waves, where sounds take on new meaning, some with dangerous implications.

Humans spend most of their time in air, a medium that transmits light so well that we have no trouble seeing the shapes of objects in a room or mountains many miles away. In the same way, water is the right medium for sound, which shapes the world of marine mammals and other species that live under water.

The hour-long documentary film reveals how humpback whales use low-frequency sounds to communicate with other whales across an entire ocean and how killer whales use high-frequency sound to locate their prey in dark waters.

“The whales see the ocean through sound, so their mind’s eye is their mind’s ear,” says Michael Jasny of the Natural Resources Defense Council, an environment group that produced the film with the help of the production company Imaginary Forces.

“Sonic Sea” opens with Ken Balcomb, dean of killer whale research in Puget Sound, telling the story of how he learned about 16 beaked whales that had beached themselves in the Bahamas, where he was doing research in 2001.

“Animals that I had grown to know over a 10-year period were now dead,” Ken says during the movie, recalling the horrifying day when one whale after another was discovered dead or dying. “They were trying to get away. I was driven to find out why.”

Thanks to Ken’s presence during that stranding incident, experts were able to prove that Navy sonar could be deadly. It took two years for Navy officials to overcome their denial.

As I watched the film, I wondered if people would identify with the idea that hearing to marine mammals is like sight to humans. Would people see how much humans have invaded the underwater world with noise from ship traffic, oil exploration, military training and shoreline construction?

“I listen to the world, and to me song is life,” said Chris Clark, a bioacoustics expert at Cornell Lab of Ornithology,. “It is the essence of who we are, and it joins us all. The problem is, in the ocean, we are injecting enormous amounts of noise, so much so that we are acoustically bleaching the ocean. All the singing voices of the planet are lost in that cloud of noise.”

This type of human invasion is different from wiping out habitat as new construction changes the land, but the effect can be equally devastating to some species.

In September of 2001, a group of researchers on the East Coast were collecting fecal samples from right whales to check for stress hormones. Stress levels were running high among the whales, except for a few days when the levels dropped dramatically. That happened right after Sept. 11, when ship traffic in the area was shut down following the bombing of the World Trade Center. It still isn’t clear what that constant stress is doing to the animals, but it can’t be good. See Duke University press release.

The good news, the film tells us, is that ships can be made quieter, with an important side benefit: Quieter ships are more efficient, which makes them cheaper to operate. Ships can also reduce noise by going slower, saving on fuel. Beyond shipping, people can find ways to operate in the ocean with less sonic harm to sea life.

The Navy’s viewpoint, as represented in the film, appears to be a more enlightened approach that I have seen until now. Of course, protecting Navy ships against enemy attacks is the priority, but the need to accommodate marine life seems to be recognized to a greater degree.

“It comes down to what we value,” Clark said. “We value a living ocean. We are putting the ocean at risk. And if you put the ocean at risk, you are putting all of us at risk.”

The first video on this page is the trailer to “Sonic Sea” as provided by the producers of the film. The second is the trailer provided by Discovery Channel.

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