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Daily fish migration linked to ocean ‘buzz’

The world’s largest migration may be responsible for the source of the sound that has been intriguing scientists for years. The low-frequency melodic buzzing has puzzled scientists all over the world but now University of California San Diego Assistant Research Biologist Simone Baumann-Pickering has recently reported at a meeting of ocean scientists in New Orleans that she thinks her team may have an answer: The daily migration of marine life from the deep, dark mesopelagic ocean up to the more comfortable and abundant epipelagic zone is responsible for the noise.

The discovery was made as scientists listened to the sounds of the deep ocean using hyrdrophones. It was evident in the Pacific ocean that a puzzling faint but continuous hum just a few decibels above the background level could be detected - and this was definitely different to the normal sound of the ocean, being 300 hertz above - higher than the call of a whale, and too continuous to be the signals of other marine mammals.

Simonene Baumann-Pickering has revealed in a study collaborating with David Checkley (Scripps Institution of Oceanography) and David Demer (Southwest Fisheries Science Center, NOAA), that the so-called Diel Vertical Migration brings as much as 10 billion metric tons of marine life out of the shadows of the dark ocean, where they spend the day in relative safety, to search for food, making it the largest migration of vertebrates in the world. Baumann-Pickering has been studying the sounds of the Pacific, but the daily migration is a staple of all the world’s oceans.

So, what causes the noise? At this stage the scientists can only speculate, but Baumann-Pickering says it could be that the creatures are “truly, actively communicating - potentially to initiate migration”, and the buzzing sound is merely a signal that “it is time to go” she says. However, there is another more mundane possibility, and that is “it’s known that some fish are considering to be farting’ declared Baumann-Pickering. The gas comes from the swim bladder that controls buoyancy, and ‘they emit gas as they change depths in the water column”.

Colleagues were told by Baumann-Pickering at the New Orleans meeting, sponsored by the American Geophysical Union that the sound poses an interesting question. Why would fish do this if, as might be expected, the sound would have the effect of attracting large predators?

At this stage nobody knows she said, “We're just scratching the surface in terms of understanding how important sound is” in the ocean.