Quiet conversation has always taken place in the ocean. Below the surface, schools of fish respond to the subtle sensations of movement nearby, dolphins navigate by piercing clicks, and whales sing over thousands of kilometres. Underwater life is connected by sound.

The intricate marine ecosystems and marine creatures have successfully relied on sound for their survival for thousands of years. Now humans are putting them in peril.

For whales and dolphins, which depend almost entirely on sound to communicate, hunt and navigate, the growing underwater noise is like living in constant static. Loud shipping traffic can mask their calls, forcing them to “shout” louder just to be heard, draining energy and disrupting feeding or mating.

From cargo ships rumbling across trade routes to oil exploration blasts echoing through the deep waters, the ocean is now one of the noisiest places on Earth. This growing sound pollution is confusing marine animals, interrupting migration paths, and threatening entire ecosystems that rely on sound to survive.

According to OceanCare, an international non-government body dedicated to marine conservation, in some ocean regions noise levels have doubled every decade since the 1950s. Noise pollution leads to animals being driven out of their habitat, makes them sick and can even kill them.

National Oceanic and Atmospheric Administration Fisheries (NOAA), the American authority responsible for management of marine life, defines this as “ocean noise pollution” – a form of environmental pollution caused by human activities that generate unnatural sound underwater. This can interfere with marine animals’ ability to hear natural sounds in the ocean, disrupting natural behaviours.

International Fund for Animal Welfare campaign manager Andreas Dinkelmeyer says that many marine species rely on sound for orientation and communication.

“Where the biological sound frequencies are masked/overlaid by human-generated sound, prey localisation and predator detection will be impaired,” he says. “Marine species health will deteriorate and will be less resilient to the numerous other threats they are facing when noise levels continue to increase.”

He says studies have shown the energy balance of harbour porpoise is greatly impacted by noise.

“Because of the noise, they are displaced from feeding grounds and have been observed to cease foraging altogether in the presence of loud ships,” Dinkelmeyer says.

“Cessation of foraging can have a severe impact on the physiological health of these species, as they are dependent on near-constant energy intake.”

Most noise generated underwater by commercial shipping is due to cavitation at the propeller. Cavitation is the physical process where water evaporates due to pressure differences. So, cavitation can be influenced and changed through adaptation of the propeller shape and design to decrease the underwater sound.

Dinkelmeyer says there is a variety of technological solutions that can reduce the underwater noise.

“Devices have been developed that improve the wake flow and thus decrease cavitation and can be mounted on existing ships, called retrofits,” he says. “An overall speed reduction of commercial vessels worldwide of a mere 10 per cent would already reduce noise levels by 40 per cent.”

Inside Climate News, an independent climate newsroom that reports on the biggest crises facing our planet, says there are slowdown programs in place dedicated to reducing noise, including Quiet Sound, which aims to help orcas in the Puget Sound, off the north-west of the United States.

In 2024, the European Commission set its first-ever cap on underwater noise levels, stating that no more than 20 per cent of marine areas can be exposed to continuous noise over one year.

Ocean Alliance science and conservation director Andy Rogan says that exposure to noise can elevate stress hormone levels in whales.

“Chronic exposure to anthropogenic noise can elevate stress hormone levels, disrupt reproductive functions, and alter behaviour,” he says. “Over time, this stress can reduce fitness, affect population health, and interfere with normal life-history activities such as feeding and breeding.”

Rogan says there are many strategies that shipping companies can adopt to decrease the amount of noise pollution.

“Shipping industries can adopt relatively low-cost strategies such as reducing vessel speeds, maintaining hulls and propellers to prevent cavitation, and investing in quieter technologies for new builds,” he says. “Many of these changes reduce fuel consumption, so quieter operations often align with cost savings and lower carbon emissions.”

Sound pollution has become one of the most overlooked threats to marine ecosystems. Unlike plastic or oil pollution, noise leaves no visible trace, but its effects are just as damaging; fortunately, it can be reversed.

The faster and larger the ships are, the louder they become. According to Ocean Care, reducing vessel speed is the most effective way, which results in an immediate reduction of underwater noise.

Seashore Engineering coastal engineer Stuart Barr says in his line of work there are restrictions they must adhere to around whale migration to limit the amount of noise pollution.

“One of the controls we have got is the timing of projects, so if we’re involved in a project that requires blasting near the coast where there is whale migration, there are restrictions and limitations on blasting or the creation of noise to minimise the impacts on the whale,” he says.

Barr says they consider the potential impacts on marine mammals when trying to balance the need for coastal development and protecting marine ecosystems via a monitoring regime.

“Anything you do at the coast, you’ve got to manage all your impacts, and one of those is the potential impact on marine mammals, being whales and dolphins, so you plan around that with your timing,” Barr says.

Before any material is dumped from dredging, for example, visual monitoring is carried out to ensure any whales or dolphins in the area have passed first, reducing the noise impact.

The oceans are predominantly an acoustic world, partly because there isn’t much light beyond 200 metres and no light at all from a depth of 1000 metres, so many marine animals are heavily reliant on the use of sound to survive.

Marine life is already struggling under the combined pressures of climate change and overfishing. According to the environmental news outlet Earth.Org, findings drawn from years of ecological monitoring highlight the urgent need to reduce human impact.

A report from the UN’s convention on the Conservation of Migratory Species of Wild Animals outlines a few possible solutions. These include cleaning and checking propellers regularly for damage; slowing down ships by 10 per cent to reduce noise impact by 40 per cent; using quieter marine vibrator systems to map out the seabed instead of seismic airguns; and restricting areas of drilling to less sensitive habitats and away from migration routes.

There are ways to turn down the volume. Slower shipping speeds, quieter engine designs, and stricter regulation of industrial noise could all help restore some of the ocean’s natural calm. But putting these solutions into practice is another challenge entirely. The ocean has always had its own music. For now, the soundtrack continues to shift, a symphony increasingly overpowered by the echoes of human activity. Whether marine life can adapt to this new rhythm remains uncertain.