Blue whale
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Classification:
Global Population
Description and Natural History
Physical DescriptionThe blue whale is the largest animal in the world.
It grows to 24 - 30 meters in length (79 - 98 feet) and perhaps weighs up to 160 tonnes (176 tons). Females are slightly larger than males. Calves are six to seven meters (20 - 23 feet) long at birth.
Blue whales are similar in body shape to other rorqual whales from the family Balaenopteridae. Blue whales have streamlined bodies and broad, flat, u-shaped rostrums similar to fin, sei, Bryde’s and minke whales. There is a large splashguard in front of the two blowholes and one ridge that runs from the front of the blowhole, ending almost at the tip of the rostrum. Blue whales are dark bluish-gray with light-colored blotches over the entire body.
Their flippers are relatively short and tapered and are light or white on the underside. The tail flukes are broad and triangular with a notch in the center and smooth trailing edges. The small dorsal fin is found about three-quarters of the way along the back and, because of the length of the animal, does not appear quickly after the whale blows at the surface. The huge ten meter (33 feet) vertical column of blow can be recognized from a distance. Blue whales have relatively short, black baleen plates and ventral grooves extending at least to the navel.
Natural History
Blue
whales inhabit all the world’s oceans, migrating long distances from tropical
and temperate waters where calves are born to Arctic and Antarctic waters where
they feed almost exclusively on krill. Blue whales tend to remain offshore, but
will come closer to feed and perhaps to breed.
There are three subspecies
recognized: the "true" blue whale, B. m. musculus, which is found in the
North Atlantic and North Pacific; the pygmy blue whale, B. m. brevicauda,
which is only found in the Sub-antarctic Zone; and B. m. intermedia, the
population that summers in the Antarctic Zone.
Blue whales are usually
found singly or in pairs but larger groups can be seen on the feeding grounds.
Blue whales may show their tail flukes slightly before a deep dive, which can
last between ten and 30 minutes. Some adults have been observed breaching but
most are young animals who breach at an angle rather than perpendicular to the
surface.
Population parameters for blue whales are not well known. They
are thought to reach sexual maturity at about ten years of age. Calves may be
born every two or three years following a 12-month gestation period. They are
weaned at about eight months and can live up to 90 years.
Today the total
"true" blue whale population is not known, but has been estimated at
approximately 5,000. Whatever the remaining population, it is only a fraction of
pre-exploitation numbers.
Status of the Species
StatusToday the blue whale is listed as Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN). It is included on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Threats to the Species
The
blue whale was spared from early hunting by its size, speed (24 - 48 kilometers,
or 15 - 30 miles, per hour when chased) and pelagic (open ocean) habits.
However, early 20th century whaling technology changed all that and the blue
whale became the ultimate whaling target, each animal yielding huge amounts of
oil (70 - 120 barrels).
For management purposes, the blue whale became
the measure against which all other whale catches were determined. A catch limit
(based on oil yield) was set for blue whales with equivalent limits for other
species based on their size compared to the blue whale. This was called the Blue
Whale Unit (BWU): one blue whale = two fin whales = 2.5 humpback whales = six
sei whales. This BWU did nothing to protect the blue whale, which had already
been hunted to economic extinction by the 1930s. Provided protection by the
International Whaling Commission (IWC) in 1965, the recovery of the blue whale
has been slow.
Current threats include disturbance from seismic
operations; collision with large vessels; entanglement in fishing gear;
pollution (including noise pollution and increasing amounts of plastic debris at
sea, oil spills and dumping of industrial wastes).
International
Trade
Listed on CITES Appendix I which prohibits international
trade.
Authors and Sources
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Blue whale. Photo © B Lehnhausen/Photo Researchers, Inc
