Blue whale Andrew Sutton
Blue whale blowhole Tim Stenton
Blue whale blow WDC/Lucy Molleson
Blue whales at surface CCC
Distinctive colour of blue whale CCC
Blue whale with calf WDC/Lucy Molleson
Tall blow of blue whale Tim Stenton
The blue whale is one of the largest animals ever to have existed on earth, and it feeds on one of the smallest. Using baleen plates (of up to 1 metre long), it filters massive swarms of krill, a tiny shrimp-like creature, from the water column. There is much debate surrounding the subspecific taxonomy of blue whales and currently there are several recognised sub-species, with the most basic division separating them into five: B. m. musculus refers to the populations of blue whale found in the north Pacific and the north Atlantic, B. m. intermedia (sometimes called the "true" blue whale) describes the Antarctic form, B. m. brevicauda (also known as the "pygmy" blue whale) describes the population found in the southern Indian Ocean (excluding Antarctica), B. m. indica has been assigned to the blue whales found in the northern Indian Ocean and B. m. unnamed subspecies refers to the population of blue whales found in Chilean waters.
The blue whale has a long, streamlined shape, pale blue or grey back with mottled, lighter blotches. The belly is usually paler and sometimes white, although a layer of algae may make it look yellow. The head of the blue whale is broad and long, up to a quarter of its total body length, and U-shaped like a gothic arch. A single ridge running along the top of the head ends in a very large splashguard in front of the two blowholes, each of which can mesaure 22 inches in diameter. The blue whale has 55 to 88 throat grooves which expand during feeding. The tongue of the blue whale weighs approximately 4 tonnes and is large enough for an entire football team to stand on. Blue whales are thought to have a life expectancy of between 60 and 120 years.
Out at sea, blue whales can be spotted during good weather at a considerable distance because of the up to 12m height of their powerful blows. They usually swim quite slowly, but can travel at over 30km/h if they are chased. Young blue whales have been seen breaching, but adults very rarely seem to do this. Often seen singly or in pairs, blue whales have loud, deep voices that carry great distances, making it possible that they are in contact with others of their own kind hundreds or even more than a thousand kilometres away. Most blue whales are thought to migrate between tropical and polar waters. In general, in winter they go to warm, low latitude tropical waters to breed and give birth. In summer they migrate to cooler, high latitude polar waters to feed. During this migration and on the winter breeding grounds, they are thought to eat virtually nothing for at least four months and live on energy from body reserves. Recent studies on the Costa Rican Dome, however, reveal that the blue whales present here are actively feeding on the winter breeding ground.
Listen to the sound of blue whales, recorded by the Australian Antarctic Division during a research expedition to Antarctica in 2015.
These ocean giants were aggressively targeted by whalers because they were a particularly valuable prize, and their populations remain greatly depleted. Hunting blue whales has been banned since 1966, but blue whale meat occasionally shows up in Japanese markets to this day labelled as that of other species. They are primarily threatened by ship strikes, noise and chemical pollution. Their IUCN status is Endangered worldwide, with some populations such as the Antarctic blue whale considered Critically Endangered.