Whales have their calls, and dolphins have their whistles. And now, researchers have eavesdropped on another group of underwater species. In a study that will be presented on Monday at the Ocean Sciences Meeting, the researchers describe a different set of noises from within the ocean. The strange sounds are made during the daily migration of fish, shrimp, jellyfish, and squid as they make their way to the water's surface where they eat. Collectively, this mass of organisms weighs about 10 billion tons, but as the American Geophysical Union notes, the researchers don't yet know which animal is responsible for the low frequency hum, but small bony fish are probably the culprits.
The hum is pretty quiet--only 3 to 6 decibels louder than the ocean's background noise, so we humans would not likely be able to hear any of it. But if we could hear it, we'd have to be within a few kilometers from the source, and the timing would have to be just right, since the dim humming only lasts for a couple of hours. Luckily these scientists deployed highly sensitive instruments to pick it up.
While we would have to try really hard to make out the sounds, predators might be specially attuned to the low hum, and since these migrating organisms are an important element in the food chain (read: they eat and get eaten), this new aural discovery could reveal a lot about the inner workings of the foodchain.
You can hear the sounds of this migration over at the American Geophysical Union's site.