Sound: an invisible pollutant

When we think of ocean pollution, most of us visualise floating plastic, oil spills, or maybe even ocean acidification from rising CO2 levels. Samantha Cargill investigates why we now have to add noise pollution to the mix, too.

Image credit: Domingo Trejo, Pixabay

Marine life exists in a world of sound. 

Almost all of the creatures in our oceans compose a beautiful underwater symphony of rhythmic pops, whirrs, clicks and whistles; an ASMR you could drift off to sleep to. Even unassuming pools left on the beach after the tide goes out can be filled with this natural music, such as the sound of sea urchins eating algae. As visibility underwater is poor, most sea creatures navigate their world using sound. Whales, for example, reflect sonar calls off underwater mountains for echolocation. 

Sound can travel almost five times faster in water than in air, and further too. Every fish studied to date has been found to possess “ears” that have specially evolved to take in the noise of their environment in order to find food and mates, and to avoid predators.

This underwater babble amounts to around 50 decibels (dB), but is being increasingly drowned out by a new threat: the immense volume of human activity in our oceans.

The onslaught of sound from human activity in our ocean is creating a crisis. 

Image credit: Pixabay

The noise level in our oceans has doubled every year since the 1950’s. Military sonar is almost as loud as an undersea earthquake (around 230 dB) and can travel for hundreds of kilometres. The extremely loud bursts of sound produced by this activity, as well as seismic surveys used to map the ocean floor, can physically harm marine life by deafening fish or bursting their swim bladders. There are increasing numbers of devastating reports of dead whales washing up on shores, many attributed to panic dives induced by noise stress. The rapid change in pressure experienced during these dives causes the bends in marine mammals, a decompression sickness that damages vital organs. Even microscopic plankton, essential to the ocean’s ecosystem, do not escape the deadly wake of seismic airguns which have been shown to kill populations, even kilometres away from the source. 

Adding to these bursts of acute noise, marine life has to contend with the chronic background noise of shipping. The low frequency drone of shipping vessels (20-200 Hz) overlaps with that of whale calls, causing disorientation and hindering communication. Imagine living with relentless roadworks outside your bedroom windows while on lockdown, day and night, with no respite. It is not surprising that shipping noises increase chronic stress in whales. 

Normally, it is difficult to study the effect of human noise on marine life as our activity is so far-reaching that there are few ‘quiet’ locations left to use as a baseline, but researchers were able to take advantage of reduced shipping off the coast of Canada following the events of 11 September 2001 to get a rare insight into the impact of sound on our oceans. They collected whale faeces to compare the level of stress-related hormones during this period of quiet with normal shipping levels. They found that under usual shipping traffic conditions, the whales were chronically stressed. Promisingly, their stress levels were able to recover to a more normal level during the sound respite. It is encouraging that ocean life may be able to return to a healthier state once noise is removed. 

What can be done to protect our marine life?

Some countries, such as Sweden and Denmark, have split shipping lanes into more channels, deconcentrating traffic in an effort to reduce noise pollution. Many modern ships have also been designed to be eco-friendlier, with quieter and more efficient propellers. Most simply of all, reducing the speed of ships can have a great reduction on the sound – even increasing journeys by 30 minutes can have major benefits. For example the Enhancing Cetacean Habitat and Observation (ECHO) programme, aiming to protect killer whale habitats, ran a trial in 2017 by asking ships to reduce their speed off Canada’s Vancouver Island. This was a success, observing a noise reduction of almost 25% in the region. However, as participation was voluntary, uptake was low, so clearly more needs to be done to convince shipping companies to adopt better practices. 

Gathering more data, such as mapping where vulnerable and endangered populations live is essential to ensure preservation. Although many animals are changing their tune, such as dolphins communicating at different frequencies to be heard over the background barrage of human noise, it is unclear if animals will fully adapt, or if this noise pollution will further drive species into extinction. With these man-made sounds travelling kilometres from its source, it seems that almost no place on earth escapes human pollution. While climate change might overall be a bigger issue, this is a crisis that can be solved easily, as the volume dial can be turned down with immediate effects. 

Written by Samantha Cargill, and edited by Ailie McWhinnie.

One thought on “Sound: an invisible pollutant

  1. Marlon Jasielczuk-Lando

    Very interesting ideas, I never considered the effect of sound disruption in the ocean. Nice article!

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