WASHINGTON The ocean has gotten noisier for decades, with man-made racket from oil drilling, shipping and construction linked to signs of stress in marine life that include beached whales and baby crabs with scrambled navigational signals.
The United States aims to change that as a federal agency prepares a plan that could force reductions in noise-making activities, including oil exploration, dredging and shipping off the nation's coast.
"We've been worried about ocean noise for decades, since the 1970s," said Richard Merrick, chief science adviser to the National Oceanographic and Atmospheric Administration (NOAA) fisheries agency and a key author of the agency's more detailed 10-year plan to be released publicly later this year. "The question is, what should we do now?"
The draft plan calls for developing noise limits and setting up a standardized listening system. It would also call for the creation of an online archive of noise data that could hold thousands of hours of recordings, which scientists could then cross-reference against data on where marine life congregates.
The plan urges more research on the effects of noise on sea creatures and more coordination with environmental and industry groups, the military and government.
Some data is in short supply, since NOAA has assessed the abundance of only 17 percent of the marine mammal species that it is mandated to monitor. Noise also takes on greater urgency with Arctic seas increasingly open to shipping and development with the melting of ice from global warming.
The scientists behind the project admit the ocean was never quiet. For millions of years it was filled with sounds ranging from the thunder of storms to the songs of whales. But fish and marine mammals evolved to coexist with those sounds, scientists note.
"A hundred years ago the ocean wasn't quiet, it was a dynamic acoustic place. But now there is a lot more human noise out there," said Jason Gedamke, head of the NOAA's ocean acoustics program.
Man-made noise from such work as pile driving, dredging, seismic air guns used in the search for oil, sonar, power-producing windmills and ice-breaking has raised the sound level dramatically.
Researchers have shown that off the coast of California, for example, underwater noise has risen several-fold in a few decades, in part from an increase in shipping.
The increased noise interferes with the sounds that marine animals use to communicate, hunt and navigate. For instance, blue whales twice the size of school buses and sleek fin whales, known as the "greyhounds of the sea" for their speed, use songs to find food and mates.
Bottlenose dolphins - the kind made popular through the 1960s TV series "Flipper" - locate objects by bouncing sound waves off them.
Fish and crab larvae use reef sounds for directions. Snapping shrimp produce collapsing bubbles whose sound waves stun prey and ward off predators.
NOAA has long required noise permits for one-off events, like drilling. The draft plan would be the first to broadly set long-term rules around noise levels.
Many oil companies already invest in quieter technology, and the European Union is also developing targets for ocean noise. The United Nations' International Maritime Organization in 2014 adopted voluntary guidelines to reduce underwater noise from ships.
The NOAA proposal has critics on the left and right.
Michael Jasny, a marine noise expert at the nonprofit Natural Resources Defense Council, said NOAA's effort was a step forward from its current tactic of muffling noisy machinery.
"Current efforts are like trying to control air pollution by putting a fence around a smokestack," he said.
The draft strategy has raised concern in the oil industry.
Andy Radford, a senior policy adviser for the American Petroleum Institute, said there was no science to support the idea of harm from the cumulative effects of underwater noise.
"We think it (is) unrealistic to try to return the seas to their prehuman condition," he said.
(Reporting by Ian Simpson; Editing by Scott Malone and Dan Grebler)