One-third of a mile below the surface of the Santa Barbara Channel sits a microphone on the ocean floor, recording every pop and song, whistle and moan, hum and click that echoes through the water.

It turns out, the ocean is a noisy place, and few places as much as the watery world off Ventura County's coast.

"The ocean is getting noisier," said Megan McKenna, a doctoral student at Scripps Institute of Oceanography, who is studying how the noise from ships affects marine life and its ability to communicate.

During the past 40 years, the number of commercial ships across the world doubled, the tonnage quadrupled and the horsepower also increased. The bigger and faster the ship, the more noisy it is.

McKenna says a joke among scientists is that you can measure America's gross domestic product by sinking an underwater microphone in the ocean.

The Santa Barbara Channel is one of the busiest shipping lanes in the world, a freeway of massive ships carrying goods to and from the Port of Hueneme and the ports of Los Angeles and Long Beach.

It also was a place where blue whales were seen in high numbers last year as they fed on the abundant food sources in the shipping lanes.

Scores of other marine mammals frequent the channel, but the call of the blue whale most closely resembles a ship's noise.

McKenna looked at the frequency of calls blue whales make while feeding and found they are in the same range as the sound coming from the ships. Both create a low "whump-whump" noise that can travel as far as 300 miles through the ocean. The ships' sound comes from the collapsing of bubbles created by the propellers, but how the whales create sound is still a mystery, McKenna said.

Her work is building on that of her professor, John Hildebrand, who has been studying how noise affects marine mammals for years. He helped build underwater microphones that have been placed in the Santa Barbara Channel, the Gulf of Mexico, Hawaii and elsewhere. It turns out, the waters of Ventura County are some of the noisiest around.

Exactly how all this noise affects the whales is still unanswered, though there are some clues.

"These animals evolved in a much quieter environment," McKenna said.

"You've got to think there has to be some threshold of them being able to use their acoustic capabilities in this noisy environment."

If whales are communicating with one another about feeding opportunities at the same frequency as the ship's noise, there's a chance the whales won't have the knowledge of food sources they normally would, McKenna said. The ships could be drowning out what the whales have to say, she said.

Ship noise could be loud enough to drown out whale calls about three hours a day, she said, when the most ships are present.

John Calambokidis, a blue whale expert who has studied the animals in the channel, said the noise could be a factor in the deaths of a number of animals that were struck by ships last year. At least three of the five blue whales that died in Southern California were hit by ships.

Studies of right whales — which got their name because whalers thought they were easy to kill, thus right' — have shown that when they hear loud noises they travel to the surface.

Blue whales could be doing the same thing when they hear ships, he said. When they are in distress and they surface, the animals could be more susceptible to being hit at such a time.

Other research suggests the whales are changing their calls to compensate for the noise, McKenna said.

McKenna said the knowledge of how the noise affects the whales may help shipbuilders find quieter ways to build propellers.

Just like carbon dioxide or tainted ballast water, "this is another pollutant that is coming out of your ship," she said. She's traveling to Europe in coming months to attend a boat-builders conference to see the feasibility of building a quieter ship.

Robert Ovetz, director of Seaflow, a Bay Area-based group that is fighting noise pollution in the sea, said he'd like a speed limit to be imposed in California's four national marine sanctuaries in order to quell some of the noise. Currently, ships have no speed limits.

"Our marine sanctuaries are being violated by these superhighways of the sea," he said.