Science, Tech, Math › Animals & Nature What Is the Biggest Animal in the Ocean? Share Flipboard Email Print eco2drew / Getty Images Animals & Nature Marine Life Marine Life Profiles Marine Habitat Profiles Sharks Key Terms Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Forestry Dinosaurs Evolution View More By Jennifer Kennedy Marine Science Expert M.S., Resource Administration and Management, University of New Hampshire B.S., Natural Resources, Cornell University Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation. our editorial process Jennifer Kennedy Updated October 03, 2019 The biggest animal in the world is a mammal that lives in the ocean. It is the blue whale (Balaenoptera musculus), a sleek, blue-gray giant. About the Blue Whale Classification Blue whales are a type of baleen whale known as a rorqual, the largest group of baleen whales. Baleen whales are characterized by the flexible filter in their gaping mouths that they use for sifting tiny prey from the water. Blue whales are filter-feeders, not fierce hunters. They drift slowly through the water and feed leisurely and opportunistically. Size Blue whales are thought to be the largest animal ever to live on the Earth, let alone the largest animal still living. They can reach lengths of up to 100 feet and weight between 100 and 150 tons. Diet and Feeding Blue whales, like other whales with baleen, eat only very small organisms. Because of their mammoth size, it takes massive amounts of tiny fish and crustaceans to satisfy a blue whale's appetite. The blue whale feeds primarily on krill and may eat up to four tons of them per day. They feed seasonally and store energy in their blubber for later use. Behavior These gentle mammals are mostly solitary but often travel in pairs. They migrate to warmer water when winter arrives and often feed near coastlines, the only time that they can be spotted close to the shore. Blue whales are always on the move and can communicate with each other across hundreds of miles. They reproduce a single offspring every few years and their young stay close until they no longer require their mother's milk. Where to Find Blue Whales Blue whales are found in each of the world's oceans but their populations have been severely depleted by the whaling industry. Blue whale populations had declined so much at harpoon whaling's beginning that the species was given protection from hunting in 1966 by the International Whaling Commission. It is because of this initiative that blue whales are still alive. As of 2019, there are an estimated 10,000 blue whales in the world. Blue whales prefer to live very far beneath the ocean's surface where food is plentiful and obstacles are few. Populations have been found in the northeast Pacific ocean, Indian ocean, north Atlantic ocean, and sometimes parts of the Arctic ocean. Though blue whales are much too large to be kept in captivity, they can be seen if you know where and when to look. To have a chance at seeing a blue whale in the wild, try whale watching off the coast of California, Mexico, or Canada during the summer and fall. Other Big Ocean Animals The sea is full of huge creatures. Here are a few more of them. Fin whale: The second largest animal in the ocean is the fin whale, another baleen whale. These slippery mammals come in at an average length of 70 feet.Whale shark: The largest fish is the whale shark, which can grow to be about 65 feet and weigh up to about 75,000 pounds. These also live on a diet of krill and plankton!Lion's mane jelly: The largest jellyfish is the lion's mane jelly. It is possible that this animal could, in rare cases, surpass the blue whale in length—some estimate that its tentacles can stretch 120 feet. The Portuguese man o' war is another large jelly-like creature that is not technically a jellyfish, but a siphonophore. It is estimated that the man o' war's tentacles can be 50 feet long. Giant oceanic manta ray: The largest ray is the giant oceanic manta ray. Their wingspan can be up to 30 feet and they can weigh up to 5,300 pounds. These docile creatures live in warm waters and are commonly seen leaping several feet out of the water. They are said to have the largest brain of any fish. Sources “Blue Whale.” NOAA Fisheries Office of Protected Resources.Carwardine, Mark. "Whales, Dolphins and Porpoises." Dorling Kindersley, 2010.“Giant Manta Ray.” Oceana.Gorter, Uko. “Blue Whale.” American Cetacean Society, 2018.Mead, James G., and Joy P. Gold. "Whales and Dolphins in Question: The Smithsonian Answer Book." Smithsonian Institution Press, 2002.“The Marine Mammal Center.” The Marine Mammal Center.