Paolo Rossi Castelli 6 May 2021 7 min read

The Covid Effect: silence returns to the ocean’s depths

The drastic drop in maritime traffic has led to a considerable reduction of noise in the oceans which, if excessive, can damage marine life. 2020 has been declared “Year of the Quiet Ocean”.

We are all aware that the Covid-19 pandemic has drastically reduced tourism and air travel. Yet, it has also seen a big drop in shipping, fishing and aquaculture, as well as slowing exploration and extraction of energy sources from the sea, military and coastguard exercises, offshore platform construction and dredging in ports and canals.

All of this has fostered unique conditions for different types of environmental studies, including those used to measure noise in the sea, and the changes which occur as a result of human activities.

For this reason, researchers the world over have set up an exceptional project which analyses data from 200 oceanic hydrophones (special microphones made to record sounds in a liquid). The hydrophones are non-military and have been positioned across all five continents. The idea is to now harness this unprecedented opportunity as much as possible.

In the coming months, the network will be increased to 500 hydrophones, gathering data from equipment already placed in many areas of the world prior to the pandemic to capture the sounds made by whales and other types of marine life. Combined with other instruments and monitoring methods, such as animal marking, analysis of data from the hydrophones will make it possible to quantify the influence human activities has on the soundscape, and to understand how noise in the sea influences ocean species.

Sounds travel for thousands of kilometres

The greatest concentrations of non-military hydrophones are found along North American coastlines (Atlantic, Pacific and Arctic), Hawaii, Europe and the Antarctic, whilst in Asia-Pacific they are more fragmented and need reinforcing.

Sound travels great distances in the sea. Many marine animals use it, along with their innate natural sonar, to navigate and communicate through water. Hydrophones can pick up these low-frequency signals hundreds or even thousands of kilometres away. But noise generated by humans has an interfering effect about which little is known.

As a result, it is necessary to measure the variability and change in background noise found in marine sound landscapes, a fact highlighted by experts from the Marine Mammal Science faculty of the University of St Andrews (Scotland), who are amongst those promoting this initiative.

It is vital to understand what sound levels cause harmful effects, and where vulnerable animals can be exposed to noise which exceeds these levels. In 2011 academics from a number of international marine research centres started to develop the International Quiet Ocean Experiment (IQOE), which four years later saw the launch of the International Quiet Ocean Experiment Science Plan.

The aim was to create a series of soundscape measurements in different marine environments over time. The plan also involved declaring 2020 the Year of the Quiet Ocean.

Covid-19 has led to a change in circumstances, “silencing” oceans with an intensity the likes of which will not be seen again for many decades. For this reason, researchers from the IQOE decided to make 2020 the Year of the Quiet Ocean.

A website for gathering data

The hydrophones chiefly cover the shallow water coastal areas (the ones most heavily affected by human activities). Yet, they also include deep-sea stations which can measure the effects of sources of low-frequency noise across vast ocean areas.

The data collected are entered on IQOE’s website, in the hope they will grow in number. At the same time, researchers are working to create a global archive so that those involved will adopt standardised methods, instruments, and depths.

A new software named MANTA, developed by a team of researchers led by the University of New Hampshire, is also helping to ensure data is standardised further.

In addition, OPUS (Open Portal to Underwater Sound) is currently undergoing tests at the Alfred Wegener Institute of Bremerhaven (Germany) to promote the use of acoustic data gathered worldwide and ensure ease of access to data processed by MANTA.

Last but not least, the new network of hydrophones will continue to make a contribution to the Global Ocean Observing System (GOOS), a global joint venture to observe currents, temperature, sea level, chemical pollution, waste and other aspects linked to the sea.


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.