Underwater Noise Pollution: Restoring the Silence of the Sea
Oceans are increasingly plagued by noise pollution from human activities, turning the depths of the sea into a cacophony that seriously threatens biodiversity.
The oceans have never faced as much pressure from human activities as they do today: industrial fisheries, the omnipresence of plastics, and increased maritime traffic. These pressures reverberate through the soundscapes of the oceans, which now resemble a true underwater cacophony, profoundly impacting the biodiversity these environments host. This underwater noise pollution is not a recent issue.
These problems, denounced since the last century (by figures like Alain Bombard in the 1960s and Cousteau in the 1990s), have not improved. States have even facilitated their intensification since the end of World War II through subsidy mechanisms that disregard their impacts on marine ecosystems, as UNESCO pointed out in 2024.
XXL Ships, Noise from Plastic Pollution…
Despite Europe investing one billion euros annually to support sustainable fishing, it is not enough. At the same time, economic support for the merchant navy has led to increasingly larger supertankers. Plastics continue to be used and now form a “continent” in the open sea.
All our activities at sea generate noise that unfortunately propagates well through the depths and sometimes over very long distances, altering the natural soundscapes. In certain areas, these soundscapes are becoming increasingly complex, filled with a multitude of sounds that are extremely diverse and sometimes overlapping.
Human Influence on Underwater Soundscapes
These underwater sounds can be grouped into three main categories:
- Geophony (environmental sounds, such as rain, earthquakes, ice floes…)
- Biophony (sounds from living organisms, like whale songs and shrimp clicks…)
- Anthrophony (sounds from human activities, such as maritime traffic and sonar…)
When studying the sound quality of the oceans, the goal is to measure different criteria, such as the forms of these sounds, frequency bands, and acoustic intensities, which range from the lowest (jet skis) to the highest (TNT explosives).
It’s also important to mention exposure time, i.e., the duration of sounds present in an ecosystem. Maritime traffic generates continuous sound, particularly on “marine highways.” Oil exploration uses air guns whose explosions can be recorded up to 500 km away.
Similarly, platform constructions sometimes use explosives or pile driving to penetrate the seabed (for example, to bury the masts of offshore wind turbines). The noise from fishing boats is also increasing, as acoustic emitters (called “pingers”) are now used, though their effectiveness in limiting accidental cetacean captures remains to be confirmed.
Measuring Sounds Inaudible from Land
But how can we measure these sounds, inaudible except underwater? The surface of the ocean acts as an “acoustic mirror”: sounds remain within the marine environment, making it difficult to grasp the din of the depths.
To do this, we need to use hydrophones (waterproof microphones). Three methods can be employed:
- Hydrophones can be deployed from a boat for instant, opportunistic monitoring.
- The second approach involves installing an acoustic observatory that can remain in place for weeks or even months to continuously record a specific area, for instance, to monitor construction work or maritime traffic within a marine protected area.
- Finally, robots (autonomous sailboats or underwater gliders) can be used to monitor larger areas.
The recordings are then analyzed. Sometimes, sounds can be identified and cataloged, but the main challenge is the sheer volume of data produced, often involving systems that record 24/7. Increasingly, artificial intelligence techniques are employed to facilitate sorting, and sometimes even the assistance of anonymous internet users through “citizen science” projects.
Harmful Effects on Cetaceans and Fish
These acoustic measurements have revealed the effects of noise on certain species, starting with cetaceans that emit sounds, including echolocation, in their vital activities and social interactions.
Various scientific studies have shown the risks of acoustic masking by anthropogenic sources, changes in behavior or habitat displacement, temporary or permanent hearing loss, stress, and even strandings.
For fish, noise can cause panic or even death, especially for those with swim bladders that can burst from the shock of an acoustic wave. Recent studies have shown that even scallops and plankton are sensitive to underwater noise.
Lack of Regular Monitoring at Sea and Regulatory Challenges
International norms and regulations exist, but how effective are they? Underwater noise pollution has been a concern for the international community since the late 2000s. Some organizations advocate for its reduction, such as the United Nations and the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
Professional sectors are also addressing this issue. For example, in 2012, the International Maritime Organization issued recommendations for shipowners. In 2023, it updated its guidelines and launched the GloNoise project to assist countries in addressing the topic.
At the regional level, we can cite the Convention for the Protection of the North-East Atlantic, the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea, and Contiguous Atlantic Area (ACCOBAMS), and the Agreement on the Conservation of Small Cetaceans of the Baltic Sea, North-East Atlantic, and Irish and North Seas (ASCOBANS).
Regarding cetaceans, the International Whaling Commission opened discussions in 2008, and ten years later adopted a resolution aimed at reducing noise to diminish harmful effects.
In Europe, Underwater Noise Recognized as a Nuisance
In Europe, the Commission voted in 2008 on the Marine Strategy Framework Directive. Among the 11 indicators used to characterize the « good ecological status of the marine environment, » one specifically addresses anthropogenic sounds (D11).
Underwater noise is thus explicitly recognized as a factor of nuisance, stress, and potential mortality. The aim of the regulations is to measure sound levels and reduce them to values compatible with the sustainability of ecosystems.
Unfortunately, European partners have yet to agree on the thresholds that would define acceptable noise levels for marine ecosystems.
A Nuisance for Ecosystems Beyond Just Noise
Addressing noise pollution is therefore necessary for the conservation of ecosystems. However, this only makes sense if considered as one of the multiple anthropogenic pressures faced by the oceans.
For cetacean populations, for example, it is not only about ensuring a certain level of underwater noise, but also about evaluating fishing impacts on their territory, collision risks with boats, the presence of macro and microplastics in their habitat, and changes due to climate warming. Regularly evaluating this entire spectrum in its entirety, and comparing it year after year, is essential for accurately characterizing the health or fragility of marine species.
2025: « Year of the Sea » – A Unique Opportunity Against Underwater Noise Pollution?
In recent years, awareness of the impacts of our activities at sea has spread to decision-makers, professionals, and the general public. Documentaries, media coverage, NGOs, and even public figures like Leonardo DiCaprio have contributed to this awareness.
In France, President Macron has declared this year the « Year of the Sea, » and he will host the third edition of the United Nations Ocean Conference in Nice in June 2025. We hope that this ambitious, potentially historic international political gathering will live up to the environmental challenges. It will be vital to consolidate regulatory measures for economic activities at sea and, above all, to implement the necessary means for their enforcement. This way, the idea of a « sustainable ocean » will not remain an oxymoron.
