The Blue Whale
Blue whales are the largest animals known to have ever existed on earth. The biggest recorded animal is more than 33m long and newborn calves have already a size of 6-7m and weigh 2-3t. From the blue whale's point of view we are as heavy as a hamster is from the humans point of view. The largest blue whales live in the Southern Hemisphere. In 1947 a 190t female was reported taken off South Georgia (Antarctica). Usually adults weigh 80-150t. They are very muscular. That's where their Latin name: Balaenoptera musculus comes from. The blue whale's blow is 10-12m high which makes it easy to spot these animals from far away.
Fin whales have a similar blow which is however more slender than that of the blue whale. Blue whales belong to the baleen whales (Mysticeti) with 270 to 395 baleen plates on each side of the upper jaw. They also belong to the rorquals because of throat grooves running from the tip of the mouth to the umbilicus. Blue whales have long flippers which make up to 15% of the body length. The dorsal fin is far back on the body and is small related to body size and highly variable in shape. The fluke is wide and raised above the water surface before a dive by some animals. One big splash guard surrounds both sides and the front of the blow hole and there is a ridge going from this splash guard to the tip of the upper jaw. The whole head of the blue whale is wide and shaped like an U.
If a blue whale is close to you, you can identify this species by the mottled pigmentation which is also used to distinguish between different individuals. This pigmentation can be found on the whole body except for head and fluke. Blue whales are cosmopolitans since they occur in each of the world's oceans where they usually live far offshore. Exceptions are the St. Lawrence on the east coast of Canada and the Gulf of California. There are three to four subspecies distinguished: the Antarctic blue whale which lives in Antarctic waters, the blue whale which occurs in the Northern Hemisphere, the pygmy blue whale inhabiting the sub-Antarctic zone of the southern Indian Ocean and the south west Pacific Ocean and the great Indian rorqual which lives in the northern Indian Ocean. | Blue whales migrate between polar waters where they feed and tropical waters which they use for mating and calving like humpback whales. Blue whales feed almost exclusively on krill, a special kind of shrimps. If you are close to a blue whale you can smell the shrimps during the blow. Shrimps carry out a vertical movement every day. They live in deeper depths during daylight to escape predators which use the light to hunt food. |
During the night the shrimps come up to the water surface to feed on algae which do not occur at depth. The blue whales follow this movement since they feed at the surface in the early morning and late evening and go to depths of more than 100m to feed during the day. The longest dives recorded by whalers chasing the animal were up to 50min in duration but blue whales usually dive for 5-20min. If blue whales feed on the surface, they often lay on the side or come up vertically with their mouth wide open and break through the water surface. When the mouth is full of shrimps and water the blue whale closes it nearly completely and pushes the water out of the it before the animal swallows its food. Blue whales feed 2-4t of krill every day and therefore prefer waters with upwelling currents where productivity is high and krill occurs in dense aggregations.
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Blue whales are fast swimmers. They travel with 5-30km/h but if they are chased by a boat or another animal, they even can move as fast as 48km/h which is impressive for a 30m long animal living in the water. During feeding blue whales swim with 3-6km/h. Another fascinating thing of blue whales are their calls. Blue whales produce sounds of very low frequencies (mostly 16-25Hz). These sounds can be as loud as 190db (in 1m distance to the sound source) and therefore be heard easily for hundreds or under optimal conditions even thousands of kilometers which may cover whole ocean basins. So these animals do not have to be close together to communicate. Blue whales of the Indian Ocean are recorded to produce songs or repeated sets of sounds. Little is known about the mating behavior of blue whales. Blue whales usually are sexual mature with 8-10 years of age. Mating occurs in late fall or winter and is followed by a 10-12 months gestation period. Lactation period is another 6-8 months and precedes 6-7 months of resting. So blue whales give birth every 2-3 years. They probably live up to 80 or 90 years but little information is available about their lifespan since blue whales mostly do not die a natural death.
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