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Blue Whale

The Blue Whale (Balaenoptera musculus) is a marine mammal that is in the suborder of baleen whales. At up to 30 meters (100 feet) in length and 140 tons or more in weight, it is believed to be the largest animal ever to have lived on Earth.

Blue Whales were abundant in most oceans around the world until the beginning of the twentieth century. For the first 40 years of the twentieth century they were hunted by whalers almost to extinction. Hunting of the blue whale was outlawed 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. Before whaling the largest population (202,000 to 311,000) was in the Antarctic, but now there only remains around 2,000 in each of the North-East Pacific, the Antarctic, and the Indian Ocean. There are two more groups in the North Atlantic and at least two (possibly more) in the Southern Hemisphere.

Taxonomy and evolution

All Blue Whales are rorquals, a family that includes the Humpback Whale, the Fin Whale, the Bryde’s Whale, the Sei Whale and the Minke Whale and belong to one of seven species of whale in the genus Balaenoptera. DNA sequencing analysis show that Blue Whales are phylogenetically closer to the Humpback and Gray Whales than other species in its genus. Other common names for the Blue Whale have included the Sulphur-bottom, Sibbald’s Rorqual, the Great Blue Whale and the Great Northern Rorqual. These names are not been used in decades.

Physical description

The Blue Whale has a long body that appears stretched in comparison with the much stockier appearance of other whales. The head is flat and U-shaped and has a very defined ridge running from the blowhole to the top of the upper lips. The front part of the mouth is thick with baleen plates; around 300 plates (each one meter long) hang from the upper jaw, running half a meter back into the mouth. Between 60 and 90 grooves (called ventral pleats) run along the throat parallel to the body. These pleats assist with evacuating water from the mouth after lunge feeding (see feeding below).

The dorsal fin is small, visible only briefly during the dive sequence. The fin varies in shape from one individual to another. It is located around three-quarters of the way along the length of the body. While breathing, the whale shouts out a spectacular vertical single column blow (up to 12 m, typically 9 m) that can be seen from half a mile away on a calm day. Its lung capacity is 1,320 Galleons.
The flippers are three to four meters long. The upper side is grey with a thin white border. The lower side is white. The head and tail flippers are generally uniformly grey colored whilst the back, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform grey color all over, whilst others demonstrate a considerable variation of dark blues, grays and blacks all tightly mottled.

Blue Whales can reach speeds of 50 km/h (30 mph) over short bursts, usually when interacting with other whales, but 20 km/h (12 mph) is a more typical traveling speed. When feeding they slow down to 5 km/h (3 mph). Some Blues in the North Atlantic and North Pacific raise their tail fluke when diving. The majority, however, do not.

Blue Whales most commonly live alone or with one other individual. It is not known whether those that travel in pairs stay together over many years or form more loose relationships. In areas of very high food concentration, as many as 50 Blue Whales have been seen scattered over a small area. However, they do not form large close-knit groups as seen in other baleen species.

Size

The Blue Whale is believed to be the largest animal ever to have lived on Earth. The largest known dinosaur of the Mesozoic era was the Argentinosaurus, which is estimated to have weighed up to 90 tonnes (100 short tons). There is some uncertainty as to the biggest Blue Whale ever found. Most data comes from Blue Whales killed in Antarctic waters during the first half of the twentieth century and was collected by whalers not well-versed in standard zoological measurement techniques. The longest whales ever recorded were two females measuring 33.6 m and 33.3 m (110 ft 3 in and 109 ft 3 in) respectively. However, there are some disputes over the reliability of these measurements. The longest whale measured by scientists at the American National Marine Mammal Laboratory (NMML) was 29.9 m long (98 ft) “” about the same length as a Boeing 737 aeroplane or three double-decker buses.

A Blue Whale comes in first place when judging animal size. A Blue Whale’s tongue is so big that it is about the size of an elephant and 50 humans could stand on its tongue. Its heart is close to the size of a small car. A human baby could crawl through a Blue Whale’s arteries. During the first 7 months of its life, a baby Blue Whale drinks approximately 400 litres (100 US gallons) of milk every day. Baby Blue Whales gain weight as quickly as 90 kg (200 pounds) every 24 hours. Even at birth, they weigh up to 1350 kg (3,000 lb) ““ the same as a fully-grown hippopotamus.

Blue Whales are very difficult to weigh because of their massive size. Most Blue Whales killed by whalers were not weighed as a whole, but cut up into manageable pieces before being weighed. This caused an underestimate of the total weight of the whale, due to loss of blood and other fluids. Even so, measurements between 150 to 170 tonnes (160 and 190 short tons) were recorded of animals up to 27 m (88 ft 6 in) in length. The weight of a 30 m (98 ft) individual is believed by the NMML to be in excess of 180 tonnes (200 short tons). The largest Blue Whale accurately weighed by NMML scientists to date was a female that weighed 177 tonnes (196 short tons).

Feeding

Blue Whales feed exclusively on krill. The exact species of this zooplankton eaten by Blue Whales varies from ocean to ocean. In the North Atlantic Meganyctiphanes norvegica, Thysanoessa raschii, Thysanoessa inermis and Thysanoessa longicaudata are the usual food. In the North Pacific Euphausia pacficia, Thysanoessa inermis, Thysanoessa longipes, Thysanoessa spinifera and Nyctiphanes symplex; in the Antarctic Euphausia superba, Euphausia crystallorophias and Euphausia vallentni.

The whales always feed on the highest concentration of krill that they can find. This means that they typically feed at depth (more than 100 m) during the daytimes, and only surface feed at night. Dive times are typically ten minutes when feeding. Diving for twenty minutes is quite common. The longest recorded is thirty-six minutes (Sears 1998). The whale feeds by lunging forward at groups of krills, taking the animals and a large quantity of water into the mouth at once. The water is then squeezed out through the baleen plates by pressing the ventral pouch and tongue up against the water. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. According to Ted Dewan’s Inside the Whale and Other Animals, as well as krill, the blue whale filters small fish and squid. It may even swallow something else that was also feeding on the krill.

Life cycle

Scientists estimate that Blue Whales can live for at least eighty years. The longest recorded study of a single individual is thirty-four years, in the north-east Pacific. The whales’ only natural predator is the Orca. As many as 25% of mature Blue Whales have scars resulting from Orca attack. The rate of mortality due to such attacks is unknown..

Vocalizations

The Blue Whale is the second loudest animal in the world (the loudest is the sperm whale). A human would likely not perceive the Blue Whale as the second loudest of all animals. Blue Whale calls last between ten and thirty seconds. Additionally Blue Whales off the coast of Sri Lanka have been recorded repeatedly making “songs” of four notes duration lasting about two minutes each. Researchers believe that as this phenomenon has not been seen in any other populations, it may be unique to the B. m. brevicauda (Pygmy) subspecies.

Blue Whale


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