Blue whale is a marine mammal that is the largest known animal ever to exist. The blue whale (Balaenoptera musculus) belongs to the family Balaenopteridae, in the order Cetacea, class Mammalia.
The species is further classified within the group known as baleen whales (suborder Mysticeti), the members of which possess, in place of teeth, a row of vertical, fringed plates on either side of the roof of the mouth. Composed of the protein keratin, these plates together form a baleen, a filtering device used when the whale feeds. Toothed whales belong to the suborder Odontoceti.
Physical Characteristics (Anatomy)
The blue whale's torpedo-shaped body is, on average, about 80 feet (24 meters) long and weighs approximately 110 tons. The longest recorded blue whale was a 112-foot (34-meter) female, while the heaviest, also a female, weighed about 200 tons. In general, female blue whales are slightly larger than males of the species.
B. musculus has a baleen containing up to 400 plates on each side of the jaw. Plates toward the front of the mouth are about 20 inches (50 cm) in length; those farther back are up to 39 inches (1 meter) long. The fringes on each plate end in tufts of fine, brushy, hairlike structures that give the suborder Mysticeti its name (derived from mystax, the Greek word for moustache).
Members of Balaenopteridae, including blue whales, have a series of grooves on their underside (about 90 of them in B. musculus), running from chin to midbelly. Consequently, species in this family are also known as rorquals, from the Norwegian word for "furrow."
Blue whales have a gray to blue gray hide mottled with gray and grayish white spots. When a blue whale is feeding in polar waters, colonies of single-celled plants called diatoms may grow over most of the whale's ventral region, turning it yellow. This accounts for another common name for the species, the sulphur-bottom whale. (The blue whale is also sometimes called Sibbald's rorqual and the great northern rorqual.)
The massive head, which takes up a quarter of the body's length, is broader than in other rorqual species. A fleshy ridge runs dorsally from the front of the snout almost to the two nostrils (blowholes), located on top of the head. The shovel-like lower jaw, when closed, covers about two-thirds of the head and face, giving the blue whale a frowning, somewhat stern appearance.
The blue whale's dorsal fin, about 1 foot (30.5 cm) high, is triangular or curved, with the size and shape varying among individuals. As in all cetaceans, the tail spreads horizontally, differing from that of fish, which spreads vertically. The flukes (the blades of the tail) are triangular and the flippers, which are modified front limbs, are tapered and about 12% as long as the total body.
Blue whales are found in all of the world's oceans, occupying every latitude of open sea. In the warmer months species members head toward the earth's polar regions, migrating to temperate and subtropical waters during the winter.
An adult blue whale must consume 3,000,000 calories per day to survive. Adult humans, in contrast, can get by on about 2,000 calories per day. The blue whale's diet consists primarily of small shrimplike crustaceans called krill.
When B. musculus is feeding, its lower jaw swings downward, forming an approximately 90° angle with the body and opening the throat to cavernous proportions. The elastic furrows on the chin and underbelly add to the flexibility of the lower-jaw tissue, accommodating the gape and allowing the skin beneath the jaw to widen laterally.
Lunging at a swarm of krill, the whale gulps in up to 1,000 tons of seawater in the process. It then shuts its jaws (the furrows allowing the closed, water-filled mouth to stretch to several times its normal size) and uses its massive tongue to push the water through the baleen, which traps the flowing krill.
After the water is expelled through the mouth, the whale rakes krill off the baleen with its tongue and swallows the tiny organisms. In this way a blue whale harvests up to 4 tons of krill, or about 40 million of these creatures, per day. However, during the winter months blue whales eat little or no food, living off of stored blubber.
Despite their massiveness, blue whales can leap completely out of the ocean and are capable of swimming on their back. When it dives, B. musculus can remain submerged for 20 minutes or more.
The whale exhales through its blowholes as it reaches the surface. In contact with the outside air, the moisture in the whale's breath condenses into a spray, commonly known as the whale's blow or spout, that shoots upward about 30 feet (9 meters).
B. musculus travels alone, in pairs, or in loose groups (pods) of up to 10 individuals, although pods of 50 to 60 have been seen. A blue whale can swim at speeds of up to 30 miles (50 km) per hour but tends to prefer moving at a more leisurely 14 miles (22 km) per hour.
Although its vision is poor, B. musculus possesses acute hearing. Species members communicate with each other using a vast array of sounds, including whistles, groans, rumblings, and clickings, some of which are above or below the range of human hearing.
The specific sounds vary among blue whale populations.The whale's low, monotonic groans can be heard underwater hundreds or, in deep water, perhaps thousands of miles away.
These low, intense calls may represent long-range communication between widely separate pods, since low-frequency sounds travel farther than do high-frequency ones, and monotonic calls are less likely to become distorted over long distances.
It is thought that high-frequency sounds produced by the blue whale may be employed for echolocation, enabling the whale to find swarms of krill, while low-frequency sound pulses may be used as a form of sonar, to build sonic images of its surroundings.
B. musculus is able to breed at six to ten years of age, with females giving birth in two- to three-year intervals. Gestation is 10 to 12 months long, and each pregnancy normally produces a single calf.
Newborns, which are about 23 feet (7 meters) long and weigh approximately 2 tons, are immediately able to swim and dive. The calf nurses for about 7 months, consuming up to 130 gallons (490 liters) of its mother's milk per day.
A nursing blue whale is one of the fastest-growing organisms on earth, gaining 200 pounds (90 kg) per day. At weaning it weighs approximately 23 tons and is about 50 feet (15 meters) long. At this point the young whale can fend for itself, although it will stay with its mother for another eight months.
The adult male plays no role in raising the calf. (On occasion B. musculus will mate and produce a hybrid calf with the closely related fin whale, B. physalus). The blue whale's life span is thought to be about 80 years, but some individuals may be capable of surviving to 110 years of age.
Environmental Status and Economic Impact
Although calves are apparently at risk from predation by orcas (killer whales) and large sharks, adult blue whales, because of their size, have virtually no natural enemies. However, they have been dangerously vulnerable to commercial whalers.
Initially, whaling posed no real threat to B. musculus. Sailing ships of the 18th and 19th centuries never bothered to pursue the species, since the whale could easily outrun them.
Eventually, technological advances, including the development of steam- and diesel-powered ships and cannon-propelled harpoons, made the harvesting of blue whales feasible. This proved extremely lucrative for the whaling industry, since a single blue whale could be rendered into as many as 90 barrels of oil
A valuable commodity, whale oil was used as a heating and lamp fuel, as a lubricant, and to make candles, margarine, and soap. The light, springy material of the baleen could be employed in a variety of products, such as fishing rods, buggy whips, carriage springs, umbrella spokes, bustles, bodices, and collars.
The 1930-1931 whaling season saw almost 30,000 blue whales killed, the greatest number in a single season. With B. musculus populations dwindling, the International Whaling Commission in the mid-1960s banned all harvesting of blue whales, giving the species worldwide protection.
Before the blue whale was hunted commercially, the B. musculus population may have comprised between 225,000 and 300,000 individuals. Despite decades of protection, by the early 21st century the world population of this species was estimated to be only 10,000 to 12,000. The Convention on International Trade in Endangered Species of Wild Fauna and Flora, an international agreement, lists the blue whale as an endangered species.