Mottled, blue-gray baleen whale ( Balaenoptera musculus ), also called sulfur-bottom whale because of the yellowish diatoms on some individuals.
The largest of all animals, the blue whale reaches a maximum length of about 100 ft (30 m) and a maximum weight of 150 tons (136,000 kg). It is found alone or in small groups in all oceans. In summer it feeds on krill in polar waters, and in winter it moves toward the equator to breed. It was once the most important of the commercially hunted baleen whales, and its populations were greatly reduced. Listed as an endangered species , it is now protected.