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AnimalsBlue Whale
Blue Whale
Common Name: Blue Whale
Scientific Name: Balaenoptera Musculus
Description
 The
blue whale, Balaenoptera Musculus, is a cosmopolitan species
of baleen whale. Blue whales in the Northern Hemisphere are
generally smaller than those in the Southern Ocean. Maximum
body length in the North Atlantic was about 88.5 feet (27
m) and the largest blue whale reported from the North Pacific
was about 88 feet (26.8 m). Adults in the Antarctic can reach
a maximum body length of about 108 feet (33 m) and can weigh
more than 330,000 pounds (150,000 kg).
As
is true of other baleen whale species, female blue whales
are somewhat larger than males. Blue whales are identified
by the following characteristics: a long-body and comparatively
slender shape; a broad, flat "rostrum" when viewed from above;
a proportionately smaller dorsal fin than other baleen whales;
and a mottled gray color pattern that appears light blue when
seen through the water. Diet
Diet
The
primary and preferred diet of blue whales is krill (euphausiids).
In the North Atlantic, blue whales feed on two main euphausiid
species: Thysanoëssa inermisand Meganyctiphanes norvegica.
In addition, T. raschiiand M. norvegicahave been recorded
as important food sources of blue whales in the Gulf of St.
Lawrence. In the North Pacific, blue whales prey mainly on
Euphausia pacificaand secondarily on T. spinifera. While other
prey species, including fish and copepods, have been mentioned
in the scientific literature, these are not likely to contribute
significantly to the diet of blue whales.
Behaviour
Blue
whales do not have teeth. Hanging down from the upper jaw
are Baleen plates which look like the frayed bristles of a
giant hairbrush and are used to sieve food from seawater.
When
a blue whale eats, the pleats or grooves on its throat and
belly expand to allow it to gulp huge watery mouthfuls of
tiny, shrimplike crustaceans called Krill. Water is then forced
out between the baleen plates and the food caught on the hairy
fringes is then swallowed.
Habitat
Blue
whales inhabit sub-polar to sub-tropical latitudes. Poleward
movements in spring allow the whales to take advantage of
high zooplankton production in summer. Movement towards the
subtropics in the fall allows blue whales to reduce their
energy expenditure while fasting, avoid ice entrapment in
some areas, and engage in reproductive activities in warmer
waters of lower latitudes. Although the species is often found
in coastal waters, blue whales are thought to occur generally
more offshore than northern right whales and humpback whales.
Life
History
 Scientists
have yet to discern many details regarding the life history
of the blue whale. The best available science suggests the
gestation period is approximately 10-12 months and that blue
whale calves are nursed for about 6-7 months. Most reproductive
activity, including births and mating, takes place during
the winter. Weaning probably occurs on, or en route to, summer
feeding areas. The average calving interval is probably two
to three years. The age of sexual maturity is thought to be
5-15 years. There are no known differences in the reproductive
biology of blue whales in the North Pacific and North Atlantic
oceans.
Most
of the larger whales have a very low reproductive rate: females
only have a single calf every 2-4 years. With very small populations
this low rate of reproduction means that it may take decades
for some species to recover to their former population levels.
Even under the best conditions, it will take over a hundred
years for the right whale to recover. For some species of
whales, the calves are born during the part of the animal
cycle when the animals are in warmer waters, and the adults
are not feeding.
Special
Features or Habits
Blue
whales produce patterned sequences of powerful, low frequency
calls, some of them as low as 9 Hz (Mellinger & Clark 2003),
making them particularly suited to long-range underwater communication
(Tyack & Clark 2000). Blue whales off Western Australia had
most energy in the range 10-30Hz (McCauley et al. 2001), while
sound source levels may reach up to 188 dB re 1?Pa at 1metre
(Richardson et al. 1995). Higher frequency (up to 524Hz) blue
whale sounds, thought to be those of pygmy blue whales, have
been recorded off Western Australia (Ljungblad et al. 1997,
McCauley et al. 2001). Blue whale calls have been recorded
during the austral winter in the tropical Pacific and Indian
Oceans (Stafford et al. 2004), but have also been recorded
off the Antarctic Peninsula during winter (D.Thiele, pers.
comm.), confirming variability of migration patterns in this
species.
Location
or Region Found
Blue
whales are found in oceans worldwide and are separated into
populations by ocean basin in the North Atlantic, North Pacific,
and Southern Hemisphere. They follow a seasonal migration
pattern between summering and wintering areas, but some evidence
suggests that individuals remain in certain areas year-round.
The extent of knowledge concerning distribution and movement
varies with area and migratory routes are not well known but,
in general, distribution is driven largely by food requirements.
For example, in the Gulf of St. Lawrence blue whales prefer
deep waters where krill is concentrated.
Being
an open ocean species they are not seen near the coast but
mainly in the deeper waters off the continental shelves and
ice edges.
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