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Blue Whale

2007 Schools Wikipedia Selection. Related subjects: Mammals

                      iBlue Whale
   A drawing of a Blue Whale seen on a Faroese stamp
   A drawing of a Blue Whale seen on a Faroese stamp
   Size comparison against an average human
   Size comparison against an average human

                             Conservation status

   Endangered (EN)
               Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Mammalia
   Order:    Cetacea
   Suborder: Mysticeti
   Family:   Balaenopteridae
   Genus:    Balaenoptera
   Species:  B. musculus

                                Binomial name

   Balaenoptera musculus
   (Linnaeus, 1758)
   Blue Whale range
   Blue Whale range

   The Blue Whale (Balaenoptera musculus) is a marine mammal belonging to
   the suborder of baleen whales. At up to 30 metres (98 feet) in length
   and 177 metric tonnes (196 short tons) or more in weight, it is
   believed to be the largest animal to have ever 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 that
   century they were hunted by whalers almost to extinction. Hunting of
   the species 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. More recent research into the Pygmy
   subspecies suggest this may be an under-estimate. Before whaling the
   largest population (202,000 to 311,000) was in the Antarctic but now
   there remain only much smaller (around 2,000) concentrations 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 in the Southern
   Hemisphere.

Taxonomy and evolution

   Blue Whales are rorquals (family Balaenopteridae), a family that
   includes the Humpback Whale, the Fin Whale, the Bryde's Whale, the Sei
   Whale and the Minke Whale. The family Balaenopteridae is believed to
   have diverged from the other families of the suborder Mysticeti as long
   ago as the middle Oligocene. However, it is not known when the members
   of these families diverged from each other.

   The Blue Whale is usually classified as one of seven species of whale
   in the genus Balaenoptera; however, DNA sequencing analysis indicates
   that Blue Whales are phylogenetically closer to the Humpback
   (Megaptera) and the Gray Whale (Eschrichtius) than to other
   Balaenoptera species; should further research corroborate these
   relationships, it will be necessary to recognize the separate genus
   Sibbaldus for the Blue Whale.
   A phylogenetic tree of animals related to the Blue Whale
   Enlarge
   A phylogenetic tree of animals related to the Blue Whale

   There have been at least 11 documented cases of Blue/ Fin Whale hybrid
   adults in the wild. Aranson and Gullberg (1983) describe the genetic
   distance between a Blue and a Fin as about the same as that between a
   human and gorilla. Blue Whale/Humpback Whale hybrids are also known.

   The specific name musculus is Latin and could mean "muscular", but it
   can also be interpreted as "little mouse". Linnaeus, who named the
   species in his seminal work of 1758, would have known this and, given
   his sense of humour, may have intended the ironic double meaning. 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 have fallen into disuse in recent decades.

   Authorities classify the species into three subspecies: B. m. musculus,
   consisting of the north Atlantic and north Pacific populations, B. m.
   intermedia, the Southern Ocean population and B. m. brevicauda (also
   known as the Pygmy Blue Whale) found in the Indian Ocean and South
   Pacific. Some older authorities also list B. m. indica as a further
   separate subspecies in the Indian Ocean, but it is most likely that
   these blue whales are pygmy blue whales, and this designation does not
   therefore have a listing in the Red List of Threatened Species. Both
   subdivisions are still questioned by some scientists; genetic analysis
   may yet show there are just two true subspecies.

Physical description

   The Blue Whale has a long tapering 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 prominent 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 metre long) hang
   from the upper jaw, running half a metre 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 (see feeding below).

   The dorsal fin is small, visible only briefly during the dive sequence.
   It varies in shape from one individual to another; some only have a
   barely perceptible lump, whilst other fins are quite prominent and
   falcate. It is located around three-quarters of the way along the
   length of the body. When surfacing to breathe, the Blue Whale raises
   its shoulder and blow hole region out of the water to a greater extent
   than other large whales (such as the Fin or Sei). This can often be a
   useful clue to identifying a species at sea. Whilst breathing, the
   whale emits a spectacular vertical single column blow (up to 12 m,
   typically 9 m) that can be seen from many kilometers on a calm day. Its
   lung capacity is 5,000 litres.
   The blow of a Blue Whale
   Enlarge
   The blow of a Blue Whale
   The small dorsal fin of this Blue Whale is just visible
   Enlarge
   The small dorsal fin of this Blue Whale is just visible

   The flippers are three to four metres long. The upper side is grey with
   a thin white border. The lower side is white. The head and tail fluke
   are generally uniformly grey coloured 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 colour all over, whilst others demonstrate a considerable
   variation of dark blues, greys 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 travelling 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 about 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 in its mouth. Its heart is close to the size of a
   small car and is the largest known in any animal. A human baby could
   squeeze into a Blue Whale's aorta, which is about 9 inches in diameter.
   During the first 7 months of its life, a Blue Whale calf drinks
   approximately 400 litres (100 US gallons) of milk every day. Blue Whale
   calves gain weight as quickly as 90 kg (200 pounds) every 24 hours.
   Even at birth, they weigh up to 2700 kg (6000 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. Nevertheless, 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).

Life cycle

   A juvenile Blue Whale with its mother
   Enlarge
   A juvenile Blue Whale with its mother

   Mating starts in late autumn, and continues to the end of winter.
   Little is known about mating behaviour or even breeding grounds.
   Females typically give birth at the start of the winter once every two
   to three years after a gestation period of ten to twelve months. The
   calf weighs about two and a half tonnes and is around 7 m in length.
   Weaning takes place for about six months, by which time the calf has
   doubled in length. Sexual maturity is typically reached at eight to ten
   years by which time males are at least 20 m long (or more in the
   southern hemisphere). Females are larger still, reaching sexual
   maturity around 21 m or around the age of five.

   Scientists estimate that Blue Whales can live for at least eighty
   years; however, since individual records do not date back into the
   whaling era, this will not be known with certainty for many years yet.
   The longest recorded study of a single individual is thirty-four years,
   in the north-east Pacific (reported in Sears, 1998). The whales' only
   natural predator is the Orca. Calambokidis et al (1990) report that as
   many as 25% of mature Blue Whales have scars resulting from Orca
   attack. The rate of mortality due to such attacks is unknown.

   Blue Whale strandings are extremely uncommon and, because of the
   species' social structure, mass strandings are unheard of. However when
   strandings do occur they can become quite a public event. In 1920, a
   Blue Whale washed up near Bragar on the Isle of Lewis in the Outer
   Hebrides of Scotland. It had been shot in the head by whalers, but the
   harpoon had failed to explode. As with other mammals, the fundamental
   instinct of the whale was to try to carry on breathing at all costs,
   even though this meant beaching to prevent itself from drowning. Two of
   the whale's bones were erected just off a main road on Lewis, and
   remain a tourist attraction.

Vocalizations

   Multimedia relating to the Blue Whale
   Note that the whale calls have been sped up 10x from their original
   speed.
     * A Blue Whale song —
          + Recorded in the Atlantic (1)
     * A Blue Whale song —
          + Recorded in the Atlantic (2)
     * A Blue Whale song —
          + Recorded in the Atlantic (3)
     * A Blue Whale song —
          + Recorded in North Eastern Pacific
     * A Blue Whale song —
          + Recorded in the South Pacific
     * A Blue Whale song —
          + Recorded in the West Pacific
     * Alternatively: Listen to a spoken version of this article. —
          + n.b. the audio file was created on 13th April 2006 and does
            not reflect subsequent edits to the article
     * Problems playing the files? See media help.

   The Blue Whale is the loudest animal in the world. Estimates made by
   Cummings and Thompson (1971) and Richardson et al (1995) suggest that
   source level of sounds made by Blue Whales are between 155 and 188
   decibels when measured at a reference pressure of one micropascal at
   one metre. By comparison, a pneumatic drill is about 100 dB. A human,
   however, would likely not perceive the Blue Whale as the loudest of all
   animals. All Blue Whale groups make calls at a fundamental frequency of
   between 10 and 40 Hz, and the lowest frequency sound a human can
   typically perceive is 20 Hz. 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, reminiscent of the well-known Humpback
   Whale songs. 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.

   Scientists do not know why Blue Whales vocalize. Richardson et al
   (1995) discuss six possible reasons:
    1. Maintenance of inter-individual distance
    2. Species and individual recognition,
    3. Contextual information transmission (e.g., feeding, alarm,
       courtship)
    4. Maintenance of social organization (e.g., contact calls between
       females and males)
    5. Location of topographic features
    6. Location of prey resources

Population and whaling

   Blue whale skeleton, outside the Long Marine Laboratory at the
   University of California, Santa Cruz
   Enlarge
   Blue whale skeleton, outside the Long Marine Laboratory at the
   University of California, Santa Cruz

The hunting era

   Blue Whales are not easy to catch, kill, or retain. Their speed and
   power meant that they were often not the target of early whalers who
   instead targeted Sperm and Right Whales. As the populations of these
   other species declined, whalers increasingly hunted the largest baleen
   whales, including the Blue Whale. In 1864 Norwegian Svend Foyn equipped
   a steamboat with harpoons specifically designed for catching large
   whales. Although initially cumbersome and with a low success rate, the
   harpoon became the weapon of choice for whale hunting, and by the end
   of the nineteenth century, the population of Blue Whales in the North
   Atlantic had declined significantly.

   Hunting of Blue Whales rapidly increased around the world, and by 1925,
   the United States, Britain and Japan had joined Norway in chasing
   whales on 'catcher boats' that caught the whales and handed them onto
   huge 'factory ships' for processing. In 1930/1931, these ships killed
   29,400 Blue Whales in the Antarctic alone. By the end of World War II
   populations had been significantly depleted, and in 1946 the first
   quotas restricting international trade in whales were introduced. These
   were ineffective because of the lack of differentiation between
   species. Rare species could be hunted equally with those found in
   relative abundance. By the time Blue Whale hunting was finally banned
   in the 1960s and illegal USSR whaling halted in the 1970s by the
   International Whaling Commission, 330,000 Blue Whales had been killed
   in the Antarctic, 33,000 in the rest of the Southern Hemisphere, 8,200
   in the North Pacific, and 7,000 in the North Atlantic and the world
   population had been reduced to less than 1% of its total one hundred
   years before.

Population and distribution today

   A Blue Whale set against the backdrop of the Azores
   Enlarge
   A Blue Whale set against the backdrop of the Azores

   Since the whaling ban, it is not well known whether the global Blue
   Whale population is increasing or remaining stable. In the Antarctic,
   best estimates show a significant increase since the end of illegal
   Soviet Union whaling, but numbers remain at under 1% of their original
   levels. It has also been suggested that Icelandic and California
   populations are increasing but these increases are not statistically
   significant. The total world population was estimated to be between
   5,000 and 12,000 in 2002 although there is great uncertainty in
   available estimates for many areas. The Blue Whale remains listed as
   "endangered" on the IUCN Red List of threatened species as it has been
   since the list's inception. The largest known concentration, consisting
   of about 2,000 individuals, is the North-East Pacific population that
   ranges from Alaska to Costa Rica but is most commonly seen from
   California in summer. This group represents the best hope for a
   long-term recovery in Blue Whale population. Sometimes this population
   strays over to the North-West Pacific; infrequent sightings between
   Kamchatka and the northern tip of Japan have been recorded.

   In the Southern Hemisphere, there appear to be two distinct subspecies,
   the Antarctic blue whale and the poorly-understood Pygmy blue whale,
   found in Indian Ocean waters. Recent abundance estimates for the
   Antarctic subspecies range from 1100 to 1700. Research into the number
   of Pygmy Blues is on-going - the most recent reports suggest that there
   may be as many as 10,000 animals. If this is confirmed it will lead to
   a substantial upward revision in the global numbers.

   Migratory patterns of these subspecies are not well known. For example,
   pygmy blue whales have been recorded in the northern Indian Ocean
   (Oman, Maldives, Sri Lanka) where they may form a distinct resident
   population. In addition, the population of Blue Whales occurring off
   Chile and Peru may also be a distinct population. Some Antarctic blue
   whales approach the eastern South Atlantic coast in winter, and
   occasionally their sounds are heard off Peru, Western Australia, and in
   the northern Indian Ocean. In Chile, the Cetacean Conservation Centre,
   with support from the Chilean Navy, is undertaking extensive research
   and conservation work on a recently discovered feeding aggregation of
   the species off the coast of Chiloe Island.

   In the North Atlantic, two stocks are recognized. The first is found
   off Greenland, Newfoundland, Nova Scotia and the Gulf of Saint
   Lawrence. This group is estimated to total about 500. The second, more
   eastern group is spotted from the Açores in Spring to Iceland in July
   and August; it is presumed that the whales follow the Mid-Atlantic
   Ridge between the two volcanic islands. Beyond Iceland, Blue Whales
   have been spotted as far north as Spitsbergen and Jan Mayen though such
   sightings are rare. Scientists do not know where these whales spend
   their winters. The total North Atlantic population is between 600 and
   1500.

   Human threats to the potential recovery of Blue Whale populations
   include the accumulation of polychlorinated biphenyl (PCB) chemicals
   within the whale's blood, causing poisoning and premature death, and
   the ever-increasing amount of noise created by ocean traffic. This
   noise drowns out the noises produced by whales (see whale song), which
   may make it harder for whales to find a mate.

   Efforts to calculate the Blue Whale population more accurately are
   supported by marine mammologists at Duke University who maintain the
   OBIS-SEAMAP (Ocean Biogeographic Information System - Spatial
   Ecological Analysis of Megavertebrate Populations), a collation of
   marine mammal sighting data from around 130 sources.

   Retrieved from " http://en.wikipedia.org/wiki/Blue_Whale"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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