The ocean is getting noisier

Human activity is making the world’s oceans noisier and not enough is being done to mitigate the effect on marine life, scientists say.

Crunching data from four decades of science research – a total of 10,000 research papers from more than 500 studies around the world – a group of international researchers compared the effects of noise on land to the noisiness of the ocean and concluded much more needs to be done.

Whether it’s searching for gas deposits or mapping the seabed using sonar, the ocean is a noisy place and becoming noisier. Noise from shipping and other vessels, from sonar and from energy and construction all add to the marine soundscape, potentially making it more difficult for species such as marine mammals to communicate and induces physiological changes which forces species to change behaviour to avoid noise.

“Unlike pollution on land, underwater noise pollution gets very little attention despite the fact there are technological solutions available to mitigate ocean noise,” says Associate Professor Craig Radford from the University of Auckland’s Institute for Marine Science.

The researchers adopted the IPCC (Intergovernmental Panel on Climate Change) confidence scale to measure the evidence of increased noise beneath the waves, a scale ranging from very high confidence to low confidence on a range of measures.

Marine animals have evolved a wide range of receptors to detect sound. Studies suggest that it’s not just dolphins and whales that detect sounds underwater but an enormous range of marine life including jellyfish, crabs and fish.

Marine species also produce sound for navigation, territorial defence, foraging, socialising, rest and reproductive courtship among other things. Humpback whales for example sing complex songs as part of mating while Atlantic cod use sound to gather in large groups to coordinate spawning activity. Animals also produce mechanical sounds such as the slap of a whale’s tail on the ocean surface or shrimp producing a ‘snap’ sound when stunning prey.

But these sounds, vital for a healthy and thriving marine environment, are endangered by constant noise generated by humans. Low-frequency noise from shipping is estimated to have increased 32-fold and has been reported to disrupt travelling, foraging, socialising, communicating, rest, and a range of other behaviours of marine mammals and reduces the ability of young fishes to detect predators.

Climate change that is directly affecting ocean temperature is also a factor in noise generation because sound travels faster in a warmer ocean.
Some mitigation measures have proven successful, for example lowering shipping speeds in the Hauraki Gulf has drastically reduced Bryde’s whales deaths while shipping giant Maersk retro-fitted five large container ships which reduced low-frequency noise from propellers by 6-8 dB.

But international agreements on noise pollution are largely voluntary.

“Noise pollution from human activity is ubiquitous but at a global level, it’s not discussed anywhere near as seriously as it needs to be, it’s an issue that is often shunted aside in terms of thinking about human impacts on the ocean,” Associate Professor Radcliff says.

“Things like electric motors in ships, technologies that muffle the sound of wind farms and seismic air-guns and deep-sea mining are available but need to be deployed more widely if we are to minimise our effect on the marine environment and ensure marine species’ future.”

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