This Sound Might Mean Dinnertime in the Deep Sea

Researchers record a chorus of deep sea animals as they migrate through the ocean

A black-belly dragonfish is just one of the small fish living in the mesopelagic zone 660 to 3300 feet below the surface of the ocean. David Checkley

Every day, some of the world’s deepest oceans buzz with a strange sound as massive communities of fish, squid, and shrimp travel up and down from the depths in search of food. Now, researchers have recorded the low-frequency sound, which they believe may be a way for these animals to tell each other that it’s dinnertime.

Scientists have long known that marine mammals like dolphins and whales use sounds to communicate underwater, but according to researchers from the University of California, San Diego this could be the first evidence of smaller ocean-dwelling animals doing the same thing, Stephen Feller reports for United Press International. The sound is very low (about three to six decibels louder than the ocean’s background noise), and could signal that it is safe to swim up from deep waters to feed.

“[I]t sounds like a buzzing or humming, and that goes on for an hour to two hours, depending on the day,” UCSD research biologist Simone Baumann-Pickering said in a statement.

The animals in question usually live in the mesopelagic zone, about 660 to 3,300 feet below the surface, but rise to the surface around dusk each night to feed. During the summer of 2015, Baumann-Pickering and her colleagues lowered audio equipment into the San Diego trench to see whether any of the undersea animals made sounds during their daily migrations. After a few days, they detected the buzz at regular times: at dusk, when the animals swam up to the surface, and again at dawn when they dove back into the deep, Feller reports.

Because sound travels farther underwater than light or chemicals, this discovery could shed new light on scientists’ understanding of the undersea ecosystem. Judging by the recordings from the San Diego trench, the sound is being made by many individuals at once and could be a signal that it’s time to migrate, Baumann-Pickering said in a statement. While the sound only travels as far as a few miles, if marine animal populations in other parts of the world also make the sound it could indicate that communication using sound is more common in the ocean’s ecosystems.

Right now the scientists aren’t sure which animals might be making this sound, though they suspect it might be caused by small bony fish found throughout the mesopelagic zone. While some researchers have suspected that small fish might be able to communicate through sound, the phenomenon isn’t well-understood. However, if scientists are able to determine which animals are making the hum and what information it might carry, it could shed new light on how these organisms, which are popular prey for all sorts of surface-level marine life, fit into the undersea ecosystem.

“I think a large array of (marine) animals will show in the next 10 to 20 years that they are capable of producing and receiving sounds.” Baumann-Pickering said in a statement.

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