Disturbing the Deep: Underwater Sound Pollution and the Impact on Marine Life

Seafarers often complain about the problems posed by noise onboard ships - especially the way it can interrupt sleep. But now pressure is growing for new rules to reduce noise from ships in response to increasing evidence about the adverse effects on marine life.

Measures such as routeing schemes, slow steaming and better insulation are being put forward following a series of studies which show that underwater noise is disrupting the ability of marine animals such as whales, dolphins and seals to communicate, navigate, breed and hunt.

A project nearing completion in the UK is set to add to the pressure for change. The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) has just produced the first maps of shipping noise in UK waters.

The maps have been developed from measurements collected by special underwater noise recording equipment at sites on the seabed around the coast. They reveal that the highest noise levels are in the English Channel (especially the Dover Strait, as might be expected) and along the northeast coast, particularly off the coasts of East Anglia, Humberside, Tyneside and Aberdeen.

High noise levels were also observed in the northern North Sea, apparently linked to shipping traffic servicing oil and gas infrastructure.

The first acoustic map of waters around the UK, developed by the Centre for Environment, Fisheries and Aquaculture Science Image: CEFAS

The maps will be used to help shape a noise monitoring and assessment programme as part of the UK Marine strategy. CEFAS has also been working to examine the impacts that noise can have, to monitor trends, and to work with regulators and industry to assist in project planning to manage potential risks. A scientific paper will be published later this year to share these results more widely.

The CEFAS initiative mirrors work undertaken by the National Oceanic and Atmospheric Administration (NOAA) in the United States, which has produced a massive noise map extending into the North Atlantic. The scales - which show annual averages - range from red (115 decibels (dB) at the top) to orange and yellow, and then to green and blue (40 dB at the bottom).

In another study, researchers used underwater microphones to measure the noise created by about 1,600 ships as they passed through Haro Strait in Washington state. The two-year study found that the average intensity of noise next to all the ships was 173 underwater dB, equivalent to 111dB through the air – similar to the sound of a loud rock concert. At a distance of around 1m, the noise from an oil tanker was around 200dB and from a tug was around 170dB.

Whales, the researchers found, would typically be subjected to noise of about 60 to 90dB – around the level of a lawnmower or a vacuum cleaner. The Port of Vancouver notes that in some areas vessel noise has reduced the area some whales can communicate by 90%. 

The Port of Vancouver incentivises sound reduction to protect at-risk marine species in its waters. This image is taken from their guide to reducing noise

Measurements off the US west coast indicate that low-frequency noise levels - those that best reflect noise from commercial shipping – are increasing by around 3dB every 10 years, representing a doubling of acoustic power at those frequencies every decade.

It’s not just the decibels, however. Scientists say that marine life is being disturbed by a ‘cocktail party effect’ of noise from various sources, including oil drilling, dredging, and seismic surveys, which can travel for long distances underwater.

An experiment conducted in the early 1990s showed that sound emitted from Heard Island, near Australia, was picked up at sites in the northern and southern Atlantic and Pacific Oceans, as well as the Indian and Southern Oceans, and sound from seismic airguns was recorded from more than 4,000km (2,500 miles) away.

‘Being able to produce and detect sound is critically important to many marine species, so changes to the natural background soundscape may have more effects on ecosystem health than previously thought,’ said NOAA fisheries biologist Jason Gedamke.

Many marine species use sound to find prey, avoid predators, locate mates and offspring, guide their navigation and locate habitat, and listen and communicate with each other.

Humpback whales feeding near Juneau, Alaska. Image: Wikipedia, Public Domain

Dr Nathan Merchant, head of the CEFAS noise and bioacoustics team, told the BBC that researchers are looking into the many ways in which marine life is being affected by noise.

‘We know that chronic stress in humans, for example, can have long-term health effects, and we're concerned for the same reasons in long term health effects in seals and other marine mammals,’ he added.

The International Maritime Organisation (IMO) has, since the early 1980s, recognised the way that human health can be damaged by noise onboard ships, with the SOLAS Convention setting mandatory maximum noise level limits for machinery spaces, control rooms, workshops, accommodation and other spaces onboard.

But the IMO is now looking at ways to enhance existing nonmandatory guidelines, introduced in 2014, which aim to cut underwater noise from commercial shipping.

Efforts are concentrating on cutting noise caused by propeller cavitation – the biggest source of sound from shipping – as well as reducing the transmission of mechanical noise through the ship’s hull though changes to hull form, onboard machinery, and various operational and maintenance recommendations such as hull cleaning.

Maps showing marine traffic around the UK by type of shipping, using Marine Management Organisation data from 2015. Left to right: Non-port service craft, cargo vessels, passenger vessels

Studies suggest that reducing ship speed can be especially effective in reducing noise. Researchers in Canada, looking at the impact of noise on beluga and bowhead whales and Arctic cod, so setting future targets for underwater sound levels emanating from ships was premature and more research was needed – in particular on the measurement and reporting of underwater sound radiating from ships.

The work being carried out by the US NOAA could prove crucial to this. In 2014, the agency established a network of 10 undersea listening stations around the US designed to systematically measure ambient noise levels in the ocean.

This project is the first large-scale effort to monitor long-term changes and trends in underwater sound and, the agency says, will ‘help scientists understand what ambient ocean sound levels are now, how they are changing over time, and what impacts man-made noise could have on marine life'. 

 

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The seafarers' union, Nautilus International, provides a worldwide network of support and information to its members at every stage in their career. Nautilus offers a range of free legal services including advice and mediation on issues such as contracts, redundancy, harassment, discrimination and non-payment of wages. A 24/7 helpline is available for members providing emergency support via Skype, email, SMS or live-chat, around-the-clock.