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Scientists find sounds of deep water animal migration

A chorus of animals can be heard as a low buzzing for an hour twice a day, as the creatures move to shallow waters for feeding at dusk and while returning to the depths around dawn.
By Stephen Feller   |   Feb. 19, 2016 at 3:15 PM

NEW ORLEANS, Feb. 19 (UPI) -- Scientists have captured the sound animals make when traveling back down to depths of the ocean from surface waters for feeding, suggesting they use sound to communicate eating or other cycles, according to a new study.

The three- to six-decibel buzzing occurs for an hour or two every day, leading scientists to think it may have to do with fish, shrimp, and squid in the ocean's mesopelagic zone signaling to each other when to emerge from the depths of the ocean to eat in safety.

Scientists from the University of California San Diego will present the research, collected last year in the San Diego Trough, at the 2016 Ocean Sciences Meeting on February 22.

The mesopelagic zone is between 200 and 1000 meters below the surface of the ocean and is populated by animals that feed on microscopic plankton, and are fed on by larger predators such as tuna, birds, and marine mammals.

While dolphins and whales are already known to use sound for communication, scientists said they were unaware of other, smaller animals doing the same.

"It's not that loud, it sounds like a buzzing or humming, and that goes on for an hour to two hours, depending on the day," Simone Baumann-Pickering, an assistant research biologist at the University of California San Diego, said in a press release.

For the research, the scientists lowered equipment into the San Diego Trough during summer 2015. Their goal was to find if deep-scattering layer animals in the mesopelagic zone created sound during their dusk and dawn migrations for feeding.

The scientists detected a low-frequency buzz made by the animals as they move from deeper water to the surface at dusk, and then back down at dawn, that is about three to six decibels louder than the background noise of the ocean. The buzzing is difficult to pick up with the naked ear, but was detected by acoustic equipment and ranges from 300 to 900 Hertz.

The top graph shows the migration of animals in the mesopelagic zone up to surface waters at night to feed, and back down at daybreak. The bottom graph shows the sound associated with this migration, which happens at dusk and dawn and is outlined by rectangles. The sound, which lasts an hour or two, is 3 to 6 decibels louder than background noise, and the frequency of the sound ranges from 300 to 900 Hertz. Photo by Simone Baumann-Pickering, et al./University of California San Diego

The sound is generated by many animals simultaneously, though scientists said they're not sure which animals create the sounds and which animals detect them, or how.

Baumann-Pickering says it's likely a large array of marine animals will be found capable of producing and hearing sounds in the next few decades, and that learning to understand how this communication works will shed light on deep-sea environments.

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