Shipping noise and other sounds from human activity in oceans harm numerous marine species, according to a broad new assessment of existing research. The findings, published this month in Science, also include viable solutions—some already in use—that could buy time to address tougher problems such as ocean acidification and potentially save the lives of imperiled species such as southern resident killer whales, Maui dolphins and Atlantic cod.
The researchers say their examination of more than 500 studies of marine noise pollution provides a solid foundation of evidence to support new policies and changing industry practices to restore the health of the global ocean soundscape for marine life and people who depend on it.
Alternative practices include dampening noises associated with offshore wind farms and taking a lower-pressure approach to seismic surveys for fossil fuel deposits. Ship designs that reduce propeller noise could also help immensely, but they are costly and lack regulatory support for widespread adoption. In the meantime slower shipping speeds and rerouting vessels away from sensitive areas of the marine ecosystem could lessen the impact of the noise, the researchers say.
Sound is a critical sensory stimulus underwater, where it travels much farther than it does in air. Many marine species—from whales to larval and juvenile reef fishes and invertebrates —rely on sound to navigate, feed and reproduce. Anthropogenic noise interferes with these activities and has harmful effects on animal behavior, hearing and other bodily functions. But noise does not persist in the marine environment—unlike, for example, harmful chemicals and microplastics.
That is why policy makers seeking to triage the earth’s injuries from human activity should treat marine noise first, says Carlos M. Duarte, a biological oceanographer and marine ecologist at King Abdullah University of Science and Technology in Saudi Arabia and the study’s lead author.
“Ocean noise has always been in the hospital waiting room,” he says. “We need to get noise out of the waiting room.”
A good place to start may be shipping noise—the most pervasive anthropogenic noise in the ocean, says study co-author Nathan Merchant, a scientist in noise and bioacoustics at the U.K.’s Center for Environment Fisheries and Aquaculture Science.
About 85 percent of shipping noise comes from propellers, says Kathy Metcalf, president of Chamber of Shipping of America, an industry trade group, who was not involved in the study. Specifically, this arises from cavitation—a propeller design issue that sometimes causes a breakdown in water flow over the blades and can result in lost energy, fuel inefficiency and noise.
But propeller cavitation can be fixed. Danish shipping company Maersk spent more than $100 million in 2017 to save fuel by retrofitting vessels’ hulls and installing more efficient propellers on 11 of its container craft. Five of these ships subsequently underwent acoustical testing and were far less noisy by six to eight decibels (dB). That translates to a 75 percent reduction in acoustic energy—comparable to the decrease in marine noise in Canada’s Bay of Fundy because of reduced commerce activity after the 9/11 attacks, according to a 2012 study published in Proceedings of the Royal Society B.
But the big sticking point to adopting these noise-reducing designs is cost, says environmental policy maker Michelle Sanders, who works at Transport Canada, a federal government department, and is not an author of the study. For all but the largest companies (such as Maersk), these improvements are currently unaffordable, adds the Chamber of Shipping of America’s Metcalf.
Seismic surveys conducted for oil and gas exploration are another potential area for marine sound reduction, according to the new assessment’s authors. In 2011 ExxonMobil, Shell and French energy company Total joined forces to design, build and test a marine version of vibroseis—a quieter, proved seismic surveying technology already used on land.
Traditional ocean seismic surveying relies on compressed air released in microsecond pulses from a surface vessel to the ocean floor every 10 to 12 seconds. Marine vibroseis replaces those pulses with vibrations for a continuous, lower-amplitude signal. Tests show that vibroseis does not generate the more harmful frequencies produced by traditional seismic surveying, reduces surveying time (and thus the duration of stress on marine life), and lowers overall sound pressure levels, says Alex Loureiro, a marine biologist at the International Association of Geophysical Contractors, who was not involved in the study. Total, the French energy company, expects the first industrial fleet of marine vibrators will be in use by 2023.
One area that is ripe for reducing noise is pile driving at offshore wind farms. Acoustic bubble curtains have increasingly been used to dampen sounds from this process. Perforated pipes encircle the pile driver, blowing a wall of air bubbles that absorb and refract the noise, reducing it by as much as 15 dB. This amounts to a reduction in acoustic energy of about 95 percent, says study co-author Jennifer Miksis-Olds, an acoustic oceanographer at the University of New Hampshire’s Center for Acoustics Research and Education.
Miksis-Olds is optimistic about both solutions. “Not only are they low-hanging fruit,” she says, “but in these cases, we’re eating the fruit.”
Marine noise could also be mitigated by strategically managing traffic on the water, the researchers point out. One promising example is a voluntary program developed by the Vancouver Fraser Port Authority in British Columbia. It asks ships and tugboats to reroute away from the feeding areas of endangered southern resident killer whales and recommends slower speeds for large ships in specific waters in southwestern British Columbia to reduce underwater noise.
Ultimately, regions will need to tailor their solutions to their own shipping traffic and infrastructure, the underwater landscape and local marine life. There is no silver bullet to address underwater noise across all vessel types, says Transport Canada’s Sanders. What works for a cruise ship may not be feasible, or as effective, for a container ship.
Solutions that seem obvious may have unintended consequences, she notes. Slowing down ships generally reduces noise, but some vessels are actually louder at slower speeds. As Sanders puts it, “Scientific studies that tell the story and raise awareness, like this paper, will move us forward.”