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.