Could “silent zones” and sustainable use be the answer?

The underwater environment is acoustic. Visibility is low, and marine animals rely on sound to communicate and detect prey. Human-made noise—an often-overlooked form of pollution—disturbs these vital processes. But as NIELS KINNEGING explains, awareness is growing among marine managers that underwater noise must be managed for a healthy environment.

Humpback whales use song to communicate, while the much smaller porpoise uses bio-sonar to find prey. When human activities add noise to the marine environment, humpbacks can’t communicate properly, and porpoises cannot find their prey.

Humans have long viewed the sea as an economic opportunity to be developed. But shipping activities, seismic exploration and drilling are on the rise, while offshore wind energy has begun to look like a feasible alternative to fossil fuels. The resulting noise is adversely affecting marine life.

A short history

Awareness of underwater noise as a serious threat to marine life first began to grow at the end of the last century. After mass strandings were linked to the use of military sonar, research was started within the military environment.

In the first decade of this century, civil sources of underwater noise were recognized, and the European Marine Strategy Framework Directive (MSFD) became the first international legislation to frame underwater noise as pollution. Since then, the framework has shaped European policy on underwater noise. An expert group, TG Noise, was formed and published authoritative reports, such as monitoring guidance (in 2014) and reports on an assessment strategy and threshold values (in 2022). A number of important European Union–funded projects were conducted that established the knowledge basis for the implementation of these policies.*

At the basis of the framework is the notion of “good environmental status.” According to the MSFD, marine waters have this status if they are ecologically diverse, dynamic, clean, healthy and productive, and if their use is at a level sustainable enough to safeguard their use for current and future generations. The MSFD aims to ensure that marine waters reach and maintain this status. This requires cyclic environmental assessments, monitoring, and a programme of measures carried out by EU member states.

* Noteworthy projects are BIAS (Baltic Sea, 2013 to 2016), Jomopans (North Sea, 2018 to 2022), Jonas (Atlantic, 2019 to 2022), QuietMed (Mediterranean, 2017 to 2021), and SATURN (research, 2021 to 2025).

Three lenses for assessment

The MSFD also states that the spatial distribution, temporal extent, and levels of human-made underwater noise should not exceed those that would adversely affect populations of marine animals. The framework advocates for assessing underwater noise in three related aspects.

First, the noise level: in general, higher amplitudes (the strength or intensity of sound waves, measured in decibels) will affect marine animals more significantly than lower levels. Very high levels, such as those that might occur during explosions or piling, can cause serious injury or even death. Permanent or temporary hearing impairment may also occur. Even at lower levels, animals may flee. These responses can have serious impacts on wildlife populations and are the focus of many research projects.

The second aspect to consider is the spatial distribution of the underwater noise. Assessments generally consider what proportion of a region is affected by noise. In some areas, like the southern part of the North Sea, where shipping intensity is considerable, the average noise levels are too high everywhere. EU member states are considering designating low noise or “silent” areas as marine protected areas.

Finally, the duration of the noise should be considered in any assessment. Animals may be able to cope with short periods of high noise levels, given that these can also originate from natural sources, such as storms. However, prolonged periods may affect their health.

In 2022, the EU expert group for underwater noise defined threshold values for noise based on a combination of these three components.

Figure 19 from PAME report: Underwater noise pollution from shipping in the Arctic.
These images show the levels and distribution of underwater noise from shipping in the Arctic Ocean in March (left, maximum sea ice extent) and September (right, minimum sea ice extent, most open water for shipping), 2015. Ship noise was mapped across the Arctic for the first time by the Arctic Council’s Protection of the Marine Environment (PAME) working group in 2021. The report found a doubling of noise in parts of the Arctic over six years, from 2013 to 2019. Note: Noise is measured at 25 Hertz, weekly median Sound Exposure Levels, in units of decibels per square micropascal.Source:

Monitoring and soundscape maps

Under the MSFD, EU member states are obliged to conduct environmental monitoring. For underwater noise, a novel approach is followed. Field measurements are combined with numerical modelling to produce a suite of soundscape maps to display details of the acoustic underwater environment. Groundbreaking projects have tested this monitoring approach in a variety of sea regions. Close co-operation between member states resulted in seamless maps capable of supporting the types of assessments discussed above.

Eventually, noise mitigation measures will need to be designed and implemented. These are already compulsory for various noise sources, and in 2023, the International Maritime Organization published guidelines for the reduction of underwater-radiated noise from ships.

Regulators are now considering whether to designate marine “silent zones” in areas that are both particularly noisy and home to various species that are especially sensitive to noise. These areas could be protected by limiting ship access and requiring ships to respect noise output limitations.

Under the European policies for protecting the marine environment, major advances have been made in our knowledge of underwater noise and its effects on marine animals and ecosystems. Practical management tools to control this type of pollution are now being developed. There is still a lot of work to do, but the advances in this field over the last decade are encouraging.