Dialling down the impact of underwater noise on aquatic life
As well as being beset by pollutants such as microplastics, aquatic life also endures the harmful effects of underwater radiated noise (URN) – sound energy released from ships and boats. “As the majority of aquatic animals use sound for vital life functions, exposure to URN can disrupt their communication, feeding, navigation/migration and reproductive behaviour,” says Gerry Sutton(opens in new window), from University College Cork and project coordinator of the EU-funded SATURN(opens in new window) project.
Quantifying the problem and finding solutions
SATURN researchers benefited from laboratory experiments and field studies which helped identify the most dangerous aquatic sounds, alongside the short and long-term effects on invertebrates, fish and marine mammals. Engineers then conducted hundreds of physical scale model tests to validate theoretical noise reduction approaches based on thousands of numerical simulations. For example, state-of-the-art miniature tags attached to marine mammals revealed where, when and how wild animals are exposed to ship noise, and recorded their behavioural responses. To assess the impact of URN (both acute and cumulative) on representative aquatic species – the project developed innovative laboratory equipment, AquaVib(opens in new window) for invertebrate studies, and the MIGRADROME(opens in new window) for evaluating effects on migratory fish. These efforts enabled the SATURN biologists to expand the evidence base about URN impacts on sensitive species across key taxonomic groups. Using this knowledge, marine engineers and maritime architects then explored promising mitigation solutions at laboratory and model scale. “Optimised propeller blade shapes along with air injection systems running along the hull bottom and at the propeller all showed promise when it came to noise reduction. Guide vanes and ducts before and around propellors were also effective,” adds Sutton. Some of these will now be demonstrated at full scale under operational conditions with a selection of commercial vessels in the new EU-funded project, LOWNOISER.
Setting standards for future work
Crucially the project developed standards for terminology, methodology, tools and metrics to measure, assess and compare the impacts of noise from shipping and boats. This included spatially mapping particle motion and defining standards for sound exposure experiments to ensure that lab results could be translated to field populations. Significant results were obtained from the team’s highly controlled field measurements of vessel noise, which underpinned creation of the new shallow water URN measurement standard ISO 17208-3(opens in new window). Another noteworthy success was quantifying the differences between source level assessments carried out by the various bodies that certify a vessel’s sound profiles, such as Bureau Veritas(opens in new window) and DNV(opens in new window). The team showed how these can diverge significantly from ISO standard profiles, prompting current work to harmonise methods(opens in new window) under the auspices of the International Association of Classification Societies(opens in new window). “Our package of standardised sound signals paves the way for more consistent and comparable results when used in essential sound exposure experiments. This will offer better understanding of dose-response relationships and eventually determine critical noise thresholds,” explains Sutton.
Full steam ahead – but quieter
SATURN’s work outlining the technical, financial and operational feasibility of implementing measures to reduce the shipping industry’s acoustic footprint directly supports the EU’s Marine Strategy Framework Directive(opens in new window) – especially the achievement of Good Environmental Status. The team also succeeded in incorporating URN into Marine Spatial Planning(opens in new window), by developing an interactive online tool combining sound modelling and geographic information systems – using risk-based approaches – to assess the cumulative effects of human pressures and outline mitigation measures. The project’s detailed findings have also been shared with the Marine Environment Protection Committee(opens in new window) at the International Maritime Organization, forming a major part of the EU’s contribution to the ongoing ‘Experience Building Phase for the reduction of URN’.
