"National Geographic" says the blue whale is the largest known animal ever to live on the earth. As adults, blue whales grow more than 100 feet long and weigh up to 200 tons. In their infancy, blue whales are still one of the largest animals in the world; the average length of young blue whales is 25 feet. The blue whale is a baleen whale. Approximately 10,000 to 25,000 blue whales exist in the wild. The ESA and IUCN list this whale as endangered.
Also known as Balaenoptera physalus, the fin whale is an ESA and IUCN endangered baleen whale. These whales live in every ocean of the world. Some of the fin whale's physical characteristics are its V-shaped head and 50 to 100 groves on its belly region. Southern Hemisphere fin whales are approximately 88 feet long, making them longer than Northern Hemisphere whales, which average 74 feet.
Found in the North Atlantic and Pacific oceans, the sei whale is the third-largest baleen whale in the world, measuring 66 feet long as adults. These whales prefer moderate temperatures and avoid arctic or tropical waters. The IUCN states that approximately 1,000 to 2,100 sei whales live in the North Atlantic. Most sei whales were killed in the 18th and 19th centuries from whaling activities.
The ESA and IUCN list the humpback whale, or Megaptera novaeangliae, as endangered. The United States protects them under the Marine Mammal Protection Act and Endangered Species Act. Internationally, the International Whaling Commission has made strict rules for not hunting humpbacks. More than 10,000 species of humpback whales exist. This baleen whale grows up to 52 feet long when fully mature.
The sperm whale, or Physeter macrocephalus, receives an endangered status from the ESA, while the IUCN lists these whales as vulnerable. The National Oceanic and Atmospheric Administration estimates that 200,000 to 1.5 million sperm whales exist in the wild. The North Atlantic in U.S. waters has more than 4,700 sperm whales. Adult male sperm whales, also called bulls, reach lengths of 65 feet.