A vast number of animals, including fish, shrimp and squid, live in the ocean's mesopelagic zone -- the waters 200 to 1000 meters (660 to 3300 feet) below the surface. Taken together, these organisms weigh approximately 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 of their combined mass, these animals also play a major role in the global cycling of carbon from the atmosphere to the seafloor, researchers report. Their newest work reveals the sound of deep-water animal migration....