The Sound of Deep Ocean Migration Caught for the Very First Time

First Posted: Feb 22, 2016 07:00 AM EST

What do animals sound like when they migrate from the depths of the ocean to the surface? Scientists not only have found but have recorded the distinct sound coming from a massive community of fish, shrimp, jellies and squid as they travel up and down from the depths of the ocean to the water's surface to feed.

A vast number of animals live in the ocean's mesopelagic zone, which include waters between 660 and 3,300 feet below the surface. These organisms all together weight about 10 billion tons, and are a major link in the food chain between microscopic plankton and top predators like tuna, birds and marine mammals.

Because the mesopelagic zone is so deep, it's also dark and food is less abundant. This is why at dusk, many deep-water animals migrate to the surface waters to feed, relying on the darkness to protect them from predators. At dawn, they sink down into the depths once more.

Now, scientists have found that there's a distinct sound associated with these daily journeys up and down through the water column. The researchers used sensitive acoustic instruments to record the low-frequency hum that the animals emit as they move up to the surface to feed at dusk, and back down to deeper waters at dawn. Currently, the researchers aren't certain which animals in the mesopelagic zone are creating the sound, but small bony fish are likely suspects.

"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," said Simone Baumann-Pickering, one of the researchers, in a news release.

The sound could actually be a signal that mesopelagic zone organisms use to start migrating up to the surface or back down to the darker depths of the ocean. These findings reveal a bit more about the alien creatures that live in the ocean depths.

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