Singing whales or choir fish? Mysterious animal sounds in the depths of the sea baffled scientists

Hearing a mysterious frog-like croaking sound reverberating in the thick posidonia grass has caught the attention of marine life professionals, who have begun recording sessions to find out its source.

Hearing a mysterious, frog-like chirping echoing through the thick weeds of posidonia has caught the attention of marine life professionals, who have begun recording sessions to find out its source.

"We recorded in 30 marine grassy environments and the sound was still there," said Lucia de Yorio of the French Center for Training and Research in Mediterranean Environments.

"No one knew a gender that chirped like that," the environmental acoustician added. "It's like a real choir in a puddle of water."

"It took us three years to determine which species was responsible," she said.

When talking about music from the heart of the ocean, many people think of whale singing. But who knows the drumbeat of red piranhas?

To share the sounds of whistling, squawking, screeching and other unknown sounds that don't even have a name, scientists from nine countries are creating a global library of underwater biological sounds, called "Glubs" (Global Library of Underwater Biological Sounds).

In order to better monitor the evolution of marine life, this database aims to bring together all the underwater audio recordings made across the planet from experts but also from enthusiastic hobbyists.

Scientists have been listening to the sounds of underwater life for decades, but these recordings have often focused on a specific species, or region, according to Project Glubs, who hope to push those limits.

They assert that "their goal is to map real sound spaces, in a non-invasive way, to spy on the evolution of an ecosystem and the species that live in it, or to discover new species."

And because many fish and aquatic invertebrates are nocturnal or shy, acoustic monitoring can aid in conservation efforts, team members emphasized in a study recently published in Frontiers in Ecology and Evolution.

"With biodiversity declining around the world , there is a need to document, identify and understand the origins of marine animal sounds before their potential disappearance," said lead author Miles Parsons of the Australian Institute of Oceanography.

Multiple functions

Scientists estimated that all 126 species of marine mammals make sounds, as do about a hundred species of aquatic invertebrates and a thousand fish.

These voices performed various functions, including self-defense, warning of danger, or temptation. But there are also negative sounds, such as the sound of an animal chewing.

There are also sounds made by invertebrates or fish that are produced "only from their anatomical composition," according to study co-author Lucia de Yorio. Among these sounds, the drum-like sound that occurs in fish due to the contraction of a muscle around the gas bladder, allowing them to control the depth at which they swim.

"It makes a clicking sound," Di Yorio said. "The frequency, the rhythm and the number of beats differ from one type to another. It's like a barcode."

Thus, it becomes possible to identify a family of fish, and the World Library will make it possible to compare, for example, between the gurgling of species of grouper fish in the Mediterranean and those off Florida or the Red Sea.

But the Globes database can also be used to identify the many mysterious underwater sounds.

After months of investigating the effects of the mysterious squawks in posidonia weeds, Lucia de Yorio and her colleagues focused on a species of sea scorpion. But that was not the end of their surprises.

"We caught one, put it in a box and tried to record it. We were in the field, and we tried to record in fish tanks where there are sea scorpions, but we didn't get any result," the researcher said.

After autopsy, it was hypothesized that this species had certain muscles and tendons that contract and vibrate. "It's a stringed instrument, like an underwater guitar," explains Lucia de Yorio. But it indicates that there are other puzzles that still need to be resolved, considering that 90% of the votes recorded in the Mediterranean are unknown.