Ocean hum blamed on farting fish from twilight zone

The source of a baffling buzzing noise emanating from the midst of the Pacific Ocean, which has been driving scientists to distraction for years, may have finally been figured out: according to a team from the University of California, who dangled microphones 1000 metres into the depths, it’s probably being caused by farting fish.

The humming noise, which can be heard across vast stretches of the enormous ocean, is particularly strong around sunrise and sunset, and the scientists believe it is being made by sea creatures rising up from the mysterious mesopelagic zone to feed under cover of darkness, before sinking back down into the safety of the gloomy depths at dawn.

As they move up and down, some of these animals are thought to release gas from their bladders. This could be to assist with buoyancy, or it might even be a form of communication, but it causes a noise that’s 3 to 6 decibels louder than the background ocean noise, and which lasts for a couple of hours.

‘It’s known that some fish are considered to be farting, that they emit gas as they change depths in the water column,’ says Dr Simone Baumann-Pickering, a marine expert who worked on the study, and who recently presented the results to the recent 2016 Ocean Sciences Meeting in New Orleans.

A vast biomass of fish, shrimp, squid and crustaceans occupy the ocean’s mesopelagic zone, which lays between 200 and 1000 metres below the surface and is sometimes called the twilight zone. Collectively they weigh an estimated 10 billion tons, and provide an essential part of the food chain between tiny plankton and predators such as higher pelagic fish, birds and marine mammals.

It's not known exactly which group is responsible for the noisy gassy emissions, but bony fish are believed to be the most likely culprits.
It’s not known exactly which group is responsible for the noisy gassy emissions, but bony fish are believed to be the most likely culprits.

Marine mammals such as dolphins and whales are known to communicate using sound underwater, but sub-aquatic chatter between smaller animals, including the inhabitants of the mesopelagic area, is less understood. Baumann-Pickering said the noises could be the fishes’ way of signalling to their fellow mesopelagic zone homies that it’s time to come up and feed—a bit like a dinner bell.

‘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 told the American Geophysical Union.

Scientists are optimistic that further study of the acoustics will help them piece together a better understanding of how the marine ecosystem fits together, answering questions around predators’ ability to pick up on the noises, and assessing how the animals might be affected by climate change and commercial fishing projects.