The blue whale, Balaenoptera musculus , is the largest living animal with lengths ranging from 24-30 meters. Before the whaling industry, Antarctic blue whales could reach very large sizes, up to 30.5 meters in length and weighing over 160 tons. The animals in the northern hemisphere are smaller reaching 24-26 meters in length. In all known populations, females tend to be larger than males of the same age.
Blue whales are a light bluish gray overall, mottled with gray or grayish white.
Their bodies are very broad with two slightly concave zones above the lungs. The flippers are long, slim, and light grayish blue to white on the underside. The tail is narrow with broad, triangular flukes. These animals are most commonly seen individually or in pairs. Females give birth to a single calf every two to three years with a gestation period of approximately twelve months.