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Listening to the underwater life

When marine researchers began recording sounds in the seagrass meadows of the Mediterranean, they picked up a mysterious sound, like a frog’s croak, that echoed in the dense foliage — and nowhere else.

“We recorded over 30 sea grasses and it was always there and no one knew the species that produced this kwa! woo! poop!” said Lucia Di Iorio, a researcher in eco-acoustics at CEFREM in France.

“It took us three years to figure out which species produced that sound.”

The melodious songs of whales may be the well-known music of the underwater habitats of the world, but few people will have heard the hoarse growl of a striped gurnard or the rhythmic drumbeat of a red piranha.

Scientists are now calling for those sounds and many thousands more to be made more widely accessible.

They say a global database of the thumps, whistles and chatters of the sea will help track the diversity of aquatic life — and name mystery sounds like those Di Iorio and her colleagues have been investigating.

Experts from nine countries are working to create what they’ve dubbed the Global Library of Underwater Biological Sounds (GLUBS).

This would collect recordings from around the world and open them up to learning based on artificial intelligence and mobile phone apps used by The Vanir-exodus scientists.

While experts have been listening to life underwater for decades, the team behind GLUBS say audio collections are often narrowly focused on a specific species or geographic area.

Their initiative is part of the burgeoning work on marine “soundscapes” – collecting all the sounds in a given area to discern information about species, behavior and overall biological diversity.

Scientists say these soundscapes are a non-invasive way to “spy” underwater life.

In a paper recently published in the journal Frontiers in Ecology and Evolution, the GLUBS team said many fish and aquatic invertebrates are primarily nocturnal or hard to find, so acoustic monitoring could aid conservation efforts.

“With global biodiversity declining and people constantly changing underwater sounds, there is a need to document, quantify and understand the sources of underwater sounds from animals before they may disappear,” said lead author Miles Parsons of the Australian Institute of Marine Science.

sonic ‘bar code’

Scientists believe that all 126 species of marine mammals emit sound, as do at least 100 aquatic invertebrates and some 1,000 species of fish.

The sounds can convey a wide variety of messages — as a defense mechanism, to warn others of danger, as part of mating and reproduction — or simply be the passive sound of an animal munching on a meal.

Di Iorio, a co-author of the GLUBS paper, said that while marine mammals, like humans, learn their language of communication, the sounds of invertebrates and fish are “just their anatomy.”

Many fish produce a distinctive drumming sound using a muscle that contracts around their swim bladder.

“These dum-dum-dum-dum-dum, the frequency, rhythm and number of pulses vary from species to species. It’s very specific,” Di Iorio told AFP.

“It’s like a barcode.”

Scientists can only identify families of fish by these sounds, so with a worldwide library they can, for example, compare the booming calls of several groupers in the Mediterranean with those off the coast of Florida.

But another important use of the library, they say, could be to help identify the many unfamiliar sounds in the world’s seas and freshwater habitats.

mystery music

After many months of researching the strange eelgrass cracker, Di Iorio and her colleagues were able to point the finger at the scorpionfish.

But they struggled to explain how it made such an unusual noise—and it refused to perform for them.

They tried to catch the fish and include it in a carrier. They sank sound equipment on the seabed next to the fish. They even listened to aquariums with scorpion fish.

“Nothing,” she said.

In the end, colleagues from Belgium grabbed a camera that could record in low light and planted some sea grass on Corsica.

They managed to catch the quail! woo! sound and video of the fish making a wobbling movement.

Back in the lab, they dissected a scorpionfish and found tendons stretched along their bodies.

Their hypothesis is that the fish contracts these muscles to produce the sound.

“It’s a guitar, an underwater guitar,” said Di Iorio.

But there are many more mysteries where that comes from.

Di Iorio said that in the Mediterranean, up to 90 percent of the sounds in a given recording can be unfamiliar.

“Every time we place a hydrophone in the water, we discover new sounds,” she added.

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