The International Maritime Organization has also made building quieter ships part of its mission, and in 2014 outlined simple guidelines for engineers and manufacturers to follow. That said, NGOs such as the World Wide Fund for Nature (WWF) have noted the voluntary guidelines put out by the IMO have been largely ineffective at curbing anthropogenic ocean noise, and are calling for mandatory limitations. Natasha Brown, an IMO spokesperson, says the IMO’s guidelines are currently under review, providing an opportunity for member states and NGOs to submit proposals for further work and action on underwater noise. “For mandatory measures, this would need to come from a proposal from an [IMO] member state or states,” she adds.
Retrofitting ships would also help to reduce ocean noise. This tends to be more expensive than adjusting designs and parts for new ships, but it could be worth it if only the most problematic ships are targeted. One of Williams’ studies on noise emanating from a fleet of 1,500 ships found 50% of the noise was coming from only 15% of the vessels. So retrofitting just those ships with new, noise-reducing propellers would make a significant difference in the fleet’s overall sound impact.
Creating a financial incentive for private companies to build, buy and operate quieter ships could be another useful approach. Design adjustments already on the market, such as propellers which reduce cavitation, can also make ships more efficient and reduce carbon emissions, says Williams. For companies looking to go greener, that added benefit may be what tips the scales.
Quietening a noisy landscape
While boat noise is the most common form of anthropogenic ocean noise, other sources also create problems.
The construction and operation of offshore wind farms is among them. Many major structures offshore are built using pile drivers, which can cause sudden bursts or pulses of loud underwater sound.
Louder or higher frequency sounds like these may do more immediate damage to nearby marine life than the more chronic, lower-frequency sounds, says John Hildebrand, a professor of oceanography at the University of California. “At high intensities it may be that the noise creates physiological damage,” he says.
One way to reduce this noise is to create a bubble curtain around the sites. It’s just as it sounds, “a series of bubbles that form almost a wall and block some of the sound being emitted from a source,” explains Bailey.
However, Chapuis notes that the operation of the wind farms also produces “a constant, low frequency sound, which can represent a chronic source of noise, even if the levels are not that high”. Some researchers argue this noise should be addressed in the planning of where wind turbines are placed, as well as in the environmental impact assessments of individual projects.
Aircraft can also produce significant underwater noise, especially when they regularly take off and land at airports near bodies of water. Moving runways further away from areas that are home to sensitive marine life could help curb the problem.
