On 27 May 2025, DEMASK and SATURN joined forces in Brussels to host a collaborative workshop on acoustic metrics for underwater sound - a critical topic in marine environmental protection. The workshop brought together different experts from across Europe to discuss one deceptively simple question: how do we best measure underwater noise to assess its impact on marine life?
Over the past 15 years, various projects have developed their own ways to measure and present underwater noise in sound maps. These maps are essential tools for understanding where, when, and how marine animals might be affected by human-generated sound. But the methods and metrics used differ, making it hard to compare results across regions and projects. This workshop was an opportunity to exchange insights and reflect on lessons learned. It was held alongside the final event of the EU Horizon 2020 SATURN project, and co-organised by DEMASK.
A shared challenge: no one-size-fits-all solution
The workshop acknowledged that there's no single "best" acoustic metric for every situation. Projects differ in their goals and scope: from tracking sound exposure in specific species to supporting EU-wide environmental assessments. Participants from leading institutes such as JASCO, Quiet Oceans, SHOM, CEFAS, and TNO were represented in the workshop. Some models calculate metrics like sound energy density, dominance, or excess levels, while others explore other indexes, such as the Acoustic Noise Pressure Index (ANPIndex). These metrics help describe how noise varies across time, frequency, and location, and how that variation might affect different marine animals.
Key takeaways from the discussion
The workshop made one thing clear: the effects of underwater sound are complex. The two main effects considered relevant for continuous underwater sound are masking and behavioural disturbance. Different sound characteristics may cause different effects, and there is no consensus on which acoustic exposure metrics best predict these effects. This suggests that multiple metrics should be calculated to cover different potential impacts.
Participants discussed the need for harmonization but also recognized that knowledge is still insufficient to fully standardize methods. Some argued for harmonization to support EU-wide policy and MSFD reporting, while others emphasized the need to keep options open until impact metrics are further developed.
At the workshop, participants agreed that using multiple sound metrics is better than relying on just one, as this allows more flexibility and better comparison between projects. They also stressed the importance of choosing frequency bands and spatial details that fit the hearing and behaviour of different marine species. While monthly or annual average sound levels work well for policy purposes, keeping the full detailed data is crucial to understand shorter-term effects. And storing comprehensive data will enable better analysis in the future as our knowledge grows.
A fruitful collaboration
The workshop wrapped up with a strong sense of shared purpose and mutual learning. As workshop leaders Niels Kinneging (DEMASK) and Gerry Sutton (SATURN) and Christ Dejonghe (discussion leader and rapporteur) concluded, the event was a valuable step forward: not only for each project, but for the wider European effort to better manage and reduce underwater noise.