Proper diving in the Gulf of St. Lawrence

L ‘Landscape Atlas of the Acoustic Oceans, published this year, offers you to plunge into the waters of the St. Lawrence River to discover – visually – a healthy universe.

“We wanted to model underwater chronic noise produced by humans in order to obtain a mapping, an image,” offers Yvan Simard, Director of the Fisheries and Oceans Canada Chair in Underwater Acoustics Applied to Marine Mammals and Their Ecosystem.

It is the work of a monk, or rather, data scientists and oceanographers who specialize in acoustics. It was implemented thanks to the collaboration between researchers from the Institute of Marine Sciences (ISMER-UQAR) and longitude –Marine Environmental Research Infrastructure for Data Integration and Application Network– ISMER based network.

It took 30 months to collect, assemble, organize and illustrate the ocean sounds for an entire year – 2013 – from the mouth of the river and the Gulf of St. Lawrence, with ambient noise isolated from the noise of shipping. This ocean of data comes from 4.5 million acoustic environment maps – data captured by hydrophones. Work will resume for 2018.

“This represents 30 terabytes of data” which makes it possible to see “places where sound is strongest at the ‘t’ time of the year,” explains Underwater Acoustics Researcher at the Mauritius La Montaigne Institute, Florian Aulanier.

This tool also makes it possible to identify areas where noise pollution risks affecting, for example, the beluga, which moves and feeds thanks to echolocation.

This also makes it possible to distinguish which boats produce more sound and infrasound than others: each of the 250 boats in circulation during 2013 has its own acoustic signature, all grouped into a so-called “diffuse” model that shows the movements.. of noise pollution.

It is also possible to dissect marine transport by type of vessel (cargo ships, tankers, passenger ships, tugs, fishing boats or pleasure boats), by its size and speed, and thus to relate them to areas of sound effect.

Remember that sound travels very quickly in water – three times faster than in air – and that this marine universe is always in motion. “It is the complexity of surround acoustics, where everything is agglomerated in a spectral range going from bass to treble and where it is necessary to identify and differentiate sound sources according to space, time and frequencies. We can be overwhelmed by all these changing and moving sources,” explains hydroacoustics expert Yvan Simard. quickly”.

For example, in mid-July 2013, the hazards of sound effects were yellow (95% and +) in the river, from the mouth of the marine park to the bay, passing through the south of the island. You had to go down more than 75 meters for the dangers to dissipate significantly – the largest depth of the middle estuary is 100 metres.

Whatever the nature of these changing sounds, there is always background noise. Remaining “purr” from which the sharpest and most aggressive sounds of human navigation penetrate. “There is a lot of variability and we don’t know how marine mammals will react to a particular noise. The danger lies in wanting to give an acoustic limit to the danger, because that can depend on the individuals and the moment at which the noise occurs”, warns M. Ollanier.

So it is a world that is not at all silent – apart from Jacques-Yves Cousteau’s documentary, world of silence. The expected 2018 update may soon show a further decline in the expected calm.

Make noise pollution visible

It is a good idea to make this audio atlas available online to as many people as possible, as the Scientific Director of the Marine Mammal Research and Education Group, Robert Michaud, comments: “It allows us to visualize the universe escaping from us.. This new tool strikes the imagination and assesses the complexity of coexistence. Inside the Gulf of Saint Lawrence”.

Marine noise, associated with expanding economic activity, is a problem now recognized by all who study marine mammals and animals that share the same water column. The Saguenay-Saint-Laurent Marine Park also has a large industrial section along with extensive tourist navigation. Ships dot there year-round, though, according to data In 2017, their number increased between September and November.

“It is unlikely that we will be able to scale back this sea highway, but with this tool we can visualize areas that are quieter and recommend keeping relative calm,” Michaud adds.

Photo: NOAA