Small reductions in cargo vessel speeds lead to much quieter oceans

SATURN researchers Charlotte Rose Findlay, Laia Rojano-Doñate, Jakob Tougaard, Mark P. Johnson, and Peter Teglberg Madsen of Aarhus University have just published a new open-access article in Science Advances. The article is the cover story for this issue of the journal, and is highlighted in a ‘Focus’ piece by the editors. Read the press release below.

Read the open-access article: https://www.science.org/doi/10.1126/sciadv.adf2987

Read the focus summary: https://www.science.org/doi/10.1126/sciadv.adi7604

Above: Figure from Findlay et al (2023), illustrated by Amy Dozier

Press Release

New research in the journal Science Advances shows that the impact of shipping noise on marine mammals can be greatly and immediately reduced by slowing ships down.

Maritime shipping transports over 80% of international trade around the globe. As they move, ships emit continuous noise from their propellers and engines. Noise from ships is now the dominant source of human-made noise in marine environments with detrimental effects on marine wildlife. Marine mammals (whales, dolphins, porpoises, and seals), which use hearing to find food, detect predators and communicate, are especially vulnerable. Loud shipping noise has been shown to change marine mammal physiology and behaviour, and limit their ability to communicate with one another. Importantly, animals that are frequently exposed to ship noise can have less energy available for growth and reproduction resulting in fewer offspring.

A new study by researchers at Aarhus University as part of the European Union Horizon 2020 SATURN (Developing Solutions to Underwater Radiated Noise) project [https://www.saturnh2020.eu/] investigated three ways to reduce ship noise impacts on marine mammals: slowing down ships; modifying the propeller and hull to make them quieter; and increasing the distance between marine mammals and ships.

Dr. Findlay and colleagues found that the area impacted by vessel noise is dramatically reduced if ship source levels (the loudness of the ship) are reduced even by a small proportion. The findings show that a 6-decibel reduction in source level led to 75% less area being exposed to underwater noise from a cargo ship. This massive reduction in source level can be achieved by slowing down vessels by 20 %, for example from 20 to 16 knots.

Combining slowdowns with improvements to the ship hull and propeller, or increased distance of ships from areas with marine mammals, will reduce noise and impacts to animals even more.

“We show that moderate slowdowns are an immediate solution to the impacts of shipping noise on marine mammals. This approach does not require modifications to ships and can be supplemented by re-routing vessels away from critical habitats for animals and by changing the propeller to reduce vessel noise,” said lead author Dr. Charlotte Findlay a SATURN Postdoctoral Research Fellow at Aarhus University, Denmark.

“'We show that slowing down vessels reduces all the potential impacts of ship noise on marine mammals even if more ships are needed to make up for the slower speed” adds senior-author Professor Peter Teglberg Madsen, a zoophysiologist at Aarhus University, Denmark.

The EU Horizon 2020 SATURN project is a collaborative effort bringing together experts in bioacoustics, maritime engineering, shipping, and other fields to develop solutions to the problem of underwater noise from shipping.

Read the Article