Updated Friday, January 4, 2013 at 08:56 AM
From above, Puget Sound's deep green waters may seem a largely silent place — a hushed world of swimming fish and burrowing clams interrupted only by lapping waves, singing whales and the occasional sea lion's grunt.
But recent work by University of Washington researchers shows the opposite. Instead, the Sound's waters are a whirring barrage of grinding engine noises, mostly from passing ships and ferries.
This background noise in some shipping channels regularly meets or exceeds levels the federal government suggests may be harmful to marine life. But at the moment there is no easy way to significantly introduce a bit more quiet.
"It is concerning that the noise levels are so high," said Marla Holt, a research biologist at Seattle's Northwest Fisheries Science Center. "When you see how often this happens and how chronic the noise exposure is, that's when you start to say, 'Wow.' "
For a year, UW engineering Ph.D. student Christopher Bassett and his colleagues placed and monitored a set of underwater microphones called hydrophones in Admiralty Inlet between Whidbey Island and Port Townsend. They also deployed a device that, in real time, tracked precisely which ships sailed through that area at any moment.
They found that at least one big noisy vessel — a container ship, ferryboat or tug — was traversing that area's busy shipping lanes at least 90 percent of the time. And they found that noise in the area from these vessels averaged about 120 decibels, a threshold federal agencies discourage developers from surpassing when they seek permits for work in or near the Sound, such as building a dock or drilling for oil or gas.
"Continuous noise at that level is considered harassment of marine mammals," Bassett said. "About 50 percent of the time, we even exceed that threshold."
Bassett's work explored only a small area of Admiralty Inlet, though he suspects other heavy ship-volume areas, such as Elliott Bay, are likely the same or worse. And while he is not a biologist, some have taken an interest in his work.
Human-caused sound in the marine environment has exploded in recent decades. Since the 1960s, noise from vessels in shipping lanes has increased tenfold.
Marine biologists have grappled for more than a decade with the impact of sonar on whales and dolphins, particularly after beaked whales in warmer waters washed ashore bleeding around the brain after exposure to mid-frequency sonar.
But even in the Northwest, Dall's porpoises and killer whales are known to alter travel patterns during some Navy exercises.
Along with the impact of sonar on cetaceans, a parallel science has emerged suggesting human-caused ocean noise can be a problem for many sea creatures — not just marine mammals.
Research shows behavioral changes by everything from herring and pollock to octopus, squid and cod with even subtle elevations in ocean noise. But it's not always clear when such changes are severe enough to affect animals' survival.
"We know plenty of species of fish and marine animals react to sound, but determining how loud and at what frequency it needs to be before the reaction to it is serious is something we still don't know that much about," Bassett said.
For example, in the Northwest, concern has largely fallen on the effect of sound on endangered southern-resident killer whales. Orcas are known to shift swimming patterns in response to high-frequency noises, which might cause them to use more energy at a time when they're often struggling to get enough nutrition.
That's why whale-watching vessels once legally allowed to be 100 yards from killer whales now must stay at least 200 yards away. The whine of the engines on those smaller boats tends to be of a higher frequency.
Shipping noises are different. Most big vessels emit sounds at low frequencies, which tend not to bother orcas but travel incredibly far in water before dissipating. And while Bassett tracked noises between 20 hertz to 20 kilohertz, capturing both low- and high-frequency sounds, he only tracked the largest vessels.
"We see highest concentration of elevated noise at very low frequencies," Bassett said. "But we do see noise levels increase when ships go by all the way up to the top of the frequency range."
If workers were building a new dock in Puget Sound, federal agencies would likely ask them to mitigate noise that reaches the level already obtained by passing vessels.
But "we don't necessarily have a mechanism to regulate existing sources of sound in our marine environment," said Lynne Barre, a marine biologist at the National Marine Fisheries Service.
In part that's because there still are so many unanswered questions. For example, while research shows noise of 120 decibels clearly impacts some species, there is no shortage of animals — including marine mammals — making their way through Admiralty Inlet.
"Is it that the noise doesn't really affect them?" asked Holt. "Or is it that they don't have alternatives? Or maybe there are effects that are small, but do they accumulate over time? We don't know."
For now, the International Maritime Organization has a committee considering voluntary guidelines that would try to cut down on noise from big ships. Meanwhile, the National Oceanic and Atmospheric Administration is mapping undersea noise and revising its guidelines for what it considers acceptable, hoping to build a case down the road to encourage even greater reductions in vessel-noise pollution.
"It is a big issue," Barre said. But the response remains "a work in progress."
Craig Welch: 206-464-2093 .
KEN LAMBERT / THE SEATTLE TIMES
UW scientists have released a study showing that noise in Puget Sound from ships is already louder than our so-called "noise budget," the amount of noise we can't exceed before we start bothering animals. Above, a container ship after entering Elliott Bay Thursday.
KEN LAMBERT / THE SEATTLE TIMES
Sisuaq, an offshore support vessel, sails Thursday in Elliott Bay, where UW researchers suspect underwater noise from vessels is at high levels.