For years, marine biologists have been mystified by a strange buzzing noise that occurs in the ocean every day. They knew it wasn’t whales or dolphins, and it didn’t match other mammal communication patterns. However, the riddle is now one step closer to being answered. Researchers from the University of California, San Diego recently announced they’d discovered the source of the strange humming: it’s creatures from the mesopelagic zone in the sea, and they are either communicating – or farting.

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Assistant research biologist Simone Baumann-Pickering said the sound is caused by fish, shrimp, squid, and jellies from the dark zone 600 to 3,000 feet below the ocean’s surface. Thanks to advanced instruments, hydrophones, her team determined that these organisms were behind the mystery. They hide during the day but ascend to the surface to feed at night, right as the sound picks up.

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Just a few decibels above the regular sounds of the ocean, the sound is continuous for one to two hours every day. It occurs around dusk and dawn. Researchers say the humming could be a type of “dinner bell,” signaling other creatures to come and feed. Or, it could be those fish expelling flatulence.

“It’s known that some fish are considered to be farting; that they emit gas as they change depths in the water column,” said Baumann-Pickering. As the fish go from high pressure to low pressure and back, their swim bladders may be producing the peculiar sounds. (You can listen to it here.)

The biologists don’t yet know which fish specifically are causing the sounds, but they suspect it is a small bony fish.

All together, these deep sea creatures weigh about ten billion tons. Baumann-Pickering says that in terms of vertebrate animals, this daily occurrence could be the most massive migration on Earth.

Once scientists do determine whether they’re chatting or farting, they’ll gain insight into ocean communication, as well as an area of the ocean that’s still shrouded in secrecy.

Via Discovery News

Images via NOAA Ocean Explorer on Flickr and Wikimedia Commons