How Noise Pollution is Drowning Out the Natural Song of the Sea

Plastic is arguably the most well known source of pollution in our oceans and this is partly due to its prevalence but also because it forms a very visual multicoloured layer on our shorelines and wave crests. However, not all sources of pollution are so obvious and sometimes it is a lot harder for us to see just how interconnected our lives are with the marine world.

Noise pollution is totally invisible and whilst we may hear some of it, much of it takes place out in the open ocean and deep under the waves, leaving this a relatively unknown issue that our ocean-going species face. Just because noise is not very often talked about does not mean it is not a big issue and in fact, the increasingly loud underwater environment is putting enormous and constant amounts of stress on many animals big and small. Whilst we may picture the open ocean as a vast expanse of calm, the water is actually filled with the noises of ships' engines, military sonar activities, construction work and seismic blasts. All this sounds like it would easily give us a headache on land, yet for those underwater, the clanging and rumbling sounds are amplified. Water particles are packed more densely than particles in air, allowing the energy carried by sound waves to travel much faster. Yet sound is also refracted off the thermocline layer, further increasing the impact of noise. This means that sound bounces off a certain layer in the ocean where warm temperatures suddenly change to cooler ones, a layer known as the sound channel. With sound bouncing back upwards towards the surface, it can travel far more miles without losing any energy, meaning noises underwater are louder than the same noise on land.

However, marine animals have evolved to have a much keener sense of hearing than their terrestrial cousins as they are often dependent on sound to survive. Living in the sea, coastal areas are often cloudy due to turbid waters, with creatures such as whales maybe only seeing a body length in front of them, while those which dive deep quickly lose light. Therefore, sound is often their main method of locating food, finding mates and family and avoiding predators. So the ocean is actually an incredibly raucous place for those lucky enough to experience it as fish whoop, whales sing, shrimps crackle and dolphins click, with all these unique sounds travelling miles from their source. Yet these conversations are being drowned out in an increasingly noisy world, with shipping traffic playing a significant part.

Global shipping traffic is increasing year on year as we, consumers, demand more and more products which are manufactured around the world. The biggest container ship is thought to create about 190 underwater decibels of noise, the equivalent of a thunderclap or a jet taking off on land. Imagine how noisy that would be and then multiply it by a hundred to try and understand how many of our marine species feel in areas such as busy shipping corridors. Many studies have taken place surrounding whales and shipping noise to determine the effect that it might be having on their lives. One such study looked at North Atlantic right whales and Southern right whales; two populations of the same specie living at opposite ends of the globe. The population in the North lives close to busy shipping lanes and bustling ports and scientists found these individuals also had a much poorer body condition and believed that they are using so much energy to overcome the effects of noise pollution that it is impacting them physically. For example, these whales hunt for Chinook salmon and use echolocation to locate these prey. Yet when the water is a fuzzy mix of lots of loud noises, it is hard for them to concentrate and find what they are looking for, leaving them less successful at hunting and therefore not eating enough food.

It is very hard for scientists to discover the true impact noise has on species such as whales however, as it is simply so difficult to find areas of ocean that are quiet. For this reason, the lockdowns seen globally in 2020 provided a unique opportunity to investigate how the habits and health of these creatures change in a more silent world. A study which took place in September 2001 also had the same unique opportunity when international air traffic was suspended due to the attack on the Twin Towers and researchers discovered that stress hormones in whales significantly decreased during this quieter period. Studies such as this have lead to some positive changes in the real world; for example in Vancouver, a 30 nautical mile stretch of ocean leading to the port now has a speed limit as slower moving ships produce less noise. Despite this new rule adding almost half an hour onto their journey time, around 80% of vessels have complied, helping reduce stress in local marine mammals. Yet an increasing number of ships in the area due to the growing exports of oil is counteracting this improvement and the area still has a long way to go to protect its whale species.

There are three ways in which noise can impact our ocean species. The first is masking, which is when human sounds cover vital natural noises, such as the sound of a predator advancing or prey close by, both of which clearly impact an animal’s survival. Ship engines and other human sounds can also overpower the songs, whistles and clicks that animals use to communicate with each other over long distances, affecting individuals finding their pod. It's thought that a whale born 80 years ago would have been able to have its song heard from an astonishing 1,600 kilometres away, the distance of an ocean basin. Today, their haunting melody may only travel 160 kilometres. This leads us on to the second impact noise can have; distraction. With species such as dolphins and whales having to concentrate so much harder on communicating with their pod, vocalising louder and in a more high pitched tone, they are distracted from dangers such as predators, moving ships and fishing nets which they may become entangled in. Studies have even found that when crabs are surrounded by loud noises, they spend more time patrolling for danger and less time caring for and protecting their young. All this extra thinking, communicating and searching for danger comes at an energetic cost, resulting in less energy left to mate, feed and migrate. Disturbance is the final impact as researchers have often seen drastic behavioural changes in animals surrounded by noise. This can include abandoning an important habitat full of food and safe places to raise young or diverting off a historical migration route and taking a longer and therefore more tiring path instead. These three key impacts of noise can impact all marine species, from whales right down to zooplankton.

Shipping certainly isn't the only human activity which is contributing to the cacophony in our oceans. Mining is a growing source of noise underwater as we search for oil, gas and precious metals. Seismic surveys are used to determine whether oil and gas lie under the seabed and the technology uses large airgun arrays which fire every seven to ten seconds... and often last for weeks, maybe even months. Can you imagine trying to concentrate with the equivalent of a grenade going off every ten seconds? Not only does this increase stress levels and cause hearing damage, it also leads to dangerous changes in behaviour as seen in 2008. Narwhals usually migrate from their summer habitat before the fast-forming winter ice takes a hold but in 2008, a year filled with seismic testing, they didn't leave their habitat and instead, 1,000 of these almost mythical creatures became lethally trapped in the ice. Even zooplankton, tiny invertebrates which form the basis of the food chain, are affected by seismic testing with their numbers dropping by over 60% in the mile surrounding the survey. With surveys lasting up to a few months, this has a massive impact on the productivity in certain patches of ocean. In order to try and prevent these effects, some places have limited activities during certain months of the year when migrating or breeding animals may be present. Others will move seismic testing to 50 miles away if a whale is spotted but with noise travelling hundreds of miles under the ocean, this seems to make little headway in the issue.

Sonar technology is another massive cause of stress to marine animals and often causes some of the most acute responses. This technology is used by the military to detect submarines and creates slow rolling soundwaves which can be deafening underwater. These sonar soundwaves can reach 235 decibels and to put that into context, the world's loudest ever rock bands, including AC/DC, Kiss and Motorhead, have only ever reached between 130-140 decibels. Astonishingly, sonar can maintain a level of 140 decibels for up to 300 miles, affecting marine species in an enormous range across the ocean. Often when this training activity is carried out, animals can be seen instantly changing their behaviour, including suddenly changing direction or swimming hundreds of miles away. In severe cases, some deep diving creatures, such as whales, panic when they hear the sound of sonar and rapidly rise to the surface of the sea. However, due to the sudden change in pressure, this can cause decompression sickness, or the bends as commonly referred to by scuba divers. Instead of taking several short, slow dives in order to reach the surface, whales rise quickly and as a result, can suffer bleeding ears and eyes. In their panic, many pods of whales and dolphins become disorientated and are known to beach themselves whilst sonar activities are taking place, leaving some of our most beautiful animals stranded on beaches and coastlines. Sadly, a rise in dolphins becoming beached has been seen recently in the Black Sea, with researchers believing a rise in Russian naval activity and the subsequent noise trauma being the reason.

Last but not least, the increasing level of underwater construction, especially of renewable energy infrastructure, is causing the undersea environment to become even noisier. Wind farms for example, require steel tubes to be hammered into the seafloor to provide the base for wind turbines. In order to do this, thousands of loud, banging, constant hammer strikes are needed and this noise can travel up to 100 miles away. Several measures are already in place to reduce the impact of this, such as having an ecologist on site who reports when whales or dolphins are nearby and construction must stop until they have passed. More technological solutions which are ever-growing include using bubble curtains around the site which help insulate the noise whilst new methods of twisting piles into the seabed rather than hammering them are being explored.

As you can see, the ocean is a surprisingly loud, noisy and stressful place for many of our marine species. In the past, the only noises that would have competed on such a level would be underwater volcano explosions or earthquakes, both infrequent and short-lived. Yet unlike plastic or chemical pollution, this really does feel like a problem that we can solve, as noise can be switched off almost instantly. Of course this is unlikely but that does not mean that there aren't a variety of simple measures we can take to help get a little bit of quiet again. The military have been building silent ships for years, why can't we use this technology on some of our container ships? Why don't we consider slowing down vessels in key areas, a tactic which not only reduces noise but also makes ships more fuel efficient too. Can't military groups slowly start their sonar activities and gradually build up the noise, allowing animals to adjust and move out of the area? Currently, there are no international goals or pieces of legislation which guide noise pollution in the ocean but with this issue clearly providing yet another large stressor on our marine species, shouldn't this be in place? It's time we listen to the natural world and help the mystical songs of the sea return.

By Neve McCracken-Heywood