The Blue Whale (Balaenoptera musculus) grows up to 33 metres (110 feet) in length and weighs 200 tons or more in weight. The Blue Whale is believed to be the largest animal to have ever lived. The last sighting of Blue whales was in the San Salvador channel, off Puerto Egas, Santiago Island. Long and slender, the Blue Whales body can be various shades of bluish-grey.
The Blue Whale has a long tapering body that appears stretched in comparison with the stockier build of other whales. Their head is flat and U-shaped and has a prominent ridge running from the blowhole to the top of the upper lip. The front part of their mouth is thick with baleen plates, around 300 plates (each around one metre (3.2 feet) long) hang from the upper jaw, running 0.5 metres (1.6 feet) back into the mouth.
Between 60 and 90 grooves (called ventral pleats) run along the throat parallel to the body. These plates assist with evacuating water from the mouth after lunge feeding. The dorsal fin is small, visible only briefly during the dive sequence. Located around three-quarters of the way along the length of the body it varies in shape from one individual to another. When surfacing to breathe, the Blue Whale raises its shoulder and blowhole out of the water to a greater extent than other large whales such as the Fin whale or Sei whale.
Some Blue Whales in the North Atlantic and North Pacific raise their tail fluke when diving. When breathing, the whale emits a spectacular vertical single column blow (up to 12 metres (40 feet), typically 9 metres (30 feet)) that can be seen from a great distance on a calm day. Its lung capacity is 5,000 litres. Blue whales have twin blowholes, shielded by a large splashguard.
The Blue Whales flippers are three to four metres (10 to 13 feet) long. Their upper sides are grey with a thin white border. Their lower sides are white. Their head and tail fluke are generally uniformly grey. The Blue whales upper parts and sometimes the flippers, are usually mottled.
A Blue Whales tongue weighs around 3 tons and when fully expanded its mouth is large enough to hold up to 100 tons of food and water. Despite the size of its mouth, the dimensions of its throat are such that a Blue Whale cannot swallow an object wider than a beach ball. Its heart weighs 600 kilograms (1,320 pounds) and is the largest known in any animal.
The Blue whale always feeds in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms (8,000 pounds) of krill in a single day. This means that they typically feed at depths of more than 100 metres (330 feet) during the day and only surface feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 20 minutes are common. The longest recorded dive is 36 minutes.
Mating starts in late autumn and continues to the end of winter. Little is known about mating behaviour or breeding grounds. Female Blue Whales typically give birth once every two to three years at the start of the winter after a gestation period of ten to twelve months. The Blue Whale calf weighs about 3 tons and is around 7 metres (23 feet) in length.
During the first 7 months of its life, a Blue Whale calf drinks approximately 400 litres of milk every day. Blue Whale calves gain weight quickly, as much as 90 kilograms (200 pounds) every 24 hours. Even at birth, they weigh up to 2,700 kilograms (6,000 pounds) – the same as a fully-grown hippopotamus.
Blue Whales can reach speeds of 50 km/h (30 miles per hour) over short bursts, usually when interacting with other whales, but 20 km/h (12 mph) is a more typical travelling speed. When feeding they slow down to 5 km/h (3 mph).
As with other baleen whales, the Blue Whale’s diet consists mainly of small crustaceans known as krill, as well as small fish and squid.
Blue Whales most commonly live alone or with one other individual. It is not known whether those that travel in pairs stay together over long periods or form more loose relationships. In locations where there is a high concentration of food, as many as 50 Blue Whales have been seen scattered over a small area. However, they do not form the large close-knit groups seen in other baleen species.
Blue Whales were abundant in nearly all oceans until the beginning of the twentieth century. For over 40 years they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 Blue Whales worldwide located in at least five groups.
Blue whales conservation status is classed as endangered.