Listening to live music underwater

Last February, a group of 17 researchers from different countries, including France, called for a global library of underwater biotopes to study their region and wealth. But the underwater biophony study, how does it work?

Australia, Taiwan, the United States, China, Canada, Great Britain, Germany, New Zealand and France. Researchers from these nine states proposed in February, in an article titled “Call for the Creation of a Global Library of Underwater Biological Sounds,” The sounds of underwater species are collected on a common platform accessible to all.

What is an underwater biophone?

In a scientific document on the biotic nature of coastal ecosystems, four researchers explain that the acoustic landscape includes several components: “Biophonic, Geophonic, and Anthropophonic”which together make up “A fingerprint of the structure, functioning, and evolution of ecosystems”. An underwater biophony, which is part of the acoustic landscape, is defined as The one who collects all the sounds made by marine creatures.

In calling on researchers to create an international voice bank, the authors explained that this reference database will do “To expand our knowledge of the acoustic diversity of aquatic environments, as well as our understanding of biodiversity and the environment”.

Such a common platform would be beneficial.”To compare types, locations and registration methodsIn addition, this audio library aims to Public awareness of the importance of aquatic animal acoustic signals, the effects of noise on them, and the potential of vocal communities to provide an indication of ecosystem health.

Every animal has its own noise

The marine world has three categories of biological communication sounds: Invertebrates, fish and marine mammals. Each type has a specific sound, allowing it to be identified by the type of noise it makes.

Lucia de Yorio, an acoustic ecology researcher and one of the signatories to the call for a marine acoustic library, explains that Each sound is associated with a behavior : a territorial defense cry, a warning signal, a call to the female in the breeding season…

The researcher takes an example of grouper courtship, during which the fish changes color and follows the female it wants to seduce by performing a dance: “During this presentation, we noticed that the grouper spoke a certain sound. So we were able to relate that sound to its reproduction.”.

To communicate, underwater species are used audio ports : “They share acoustic space to make their voices better audible. They distribute the frequency, in time and space, to prevent their own frequencies from interfering with those of others. To do this, they use time windows where their voice is dominant and a few species are likely to interfere with them.”Lucia de Yorio says. This frequency distribution applies to all environments, at sea and on land.

Under water, the sounds of this marine species can be heard up to several hundred kilometers. The researcher explains, for example, that when a scallop’s shell closes to expel debris inside its shell, it emits a low-intensity noise of less than one meter. “Compared to this, the blue whale makes low-pitched sounds, which can be heard hundreds of miles away.”she adds.

How to listen to the symphony underwater?

Specialized companies are developing dedicated recorders and software for listening to underwater acoustic landscapes. Such is the case of French company Abyssens, created in 2019 by Caroline Magnier, an underwater acoustics physician. For underwater noise analysis, you use voice recorders.

Inside these instruments is a hydrophone equivalent to a microphone, which analyzes the differences in acoustic pressures and converts them back into an electrical signal. Then we retrieve this signal, record it, digitize it, save it, and study it.”, explains the founder of Abyssens. These voice recorders can stay underwater from 17 days to 6 months.

These recordings make it possible to develop audio scenes. These combinations of sounds reveal information about the habitat, its phonological diversity, or even its taxonomic types, that is, the diversity of organisms and communities of species that are there. For Lucia Di Iorio, these recordings are very useful because they are useful Biodiversity indicators that reflect the state of the habitat.

In June 2020, the French Ministry of Environmental Transformation and Solidarity published a report entitled “Recommendations to reduce the effects of anthropogenic acoustic emissions at sea on marine animals”. In this 200-page text, manufacturers are advised not to exceed certain decibel limits, so as not to affect marine animals.

“We’re talking about human pollution. There are business-related noises such as the impulsive noise of driving over rubble or explosions, but there are also continuous noises such as shoveling.”, Quoted by Doctor in Underwater Acoustics. This group of noises, produced by human activities, is called “anthropophone”.

Consequences of noise pollution

These numerous sounds, emitted for example during the passage of boats or work at sea, have consequences for marine animals. For Caroline Magnier, these sounds can be in the original behavioral disorders in some species. “The fish go down deeper into the water during the day, so as not to be too disturbed by the noise of boats. Some feed less due to stress, others get used to this stress: then we observe the phenomenon of habituation of underwater species sometimes experience Temporary or permanent disturbance of their hearingexplains the specialist in underwater acoustics.

Lucia de Yorio notes impoverishment of headphones, due to global warming, deforestation and human impact in general. She lists the range of anthropophone effects:The stress of animals exposed to noise increases, some breed less than others, pay less attention to their nests and predators, change their vocal behavior, move …

The formation of a world library of underwater biotopes began, at the request of 17 researchers, including Lucia de Yorio. This platform is useful for all kinds of audiences, Identify global sound domains and analyze their evolution over time.

The researchers who signed the article justify the need to create such an audio library as follows: “At a time when global biodiversity is significantly degraded and underwater sound landscapes are altered by human influences, there is a need to document, quantify and understand critical sound sources – potentially before they happen. They are disappearing.”.

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