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Blue Whale

The largest animal on Earth


Order: Cetacea

Suborder: Mysticeti

Family: Balaenopteridae

Genus & Species: Balaenoptera musculus (prev. Sibbaldus musculus)

APPEARANCE

As most people know, the blue whale is the largest of all the whales. Indeed, it is even the largest of all the mammals it is the largest known animal (although not the longest - giant squid have been found over 200 ft long including tentacles.)! Blue whales reach an average of 85 ft (25.5 m) in length, with the largest specimen ever caught being 94 ft (28.2 m) long. Sexual dimorphism is present, with the females being larger than the males. The blue whales in the southern hemisphere are generally larger than those in the northern hemisphere. The northern variety is typically 75-80 ft (22.5-24 m) long.

Blue whales are also the world's heaviest animals, averaging at 110 tons (99 800 kg), the equivalent of 30 elephants. The females weigh more than the males, and the heaviest specimen caught, weighing at 174 tons (157 900 kg), was female.

The blue whale has a long, streamlined body that tapers off to form a tail, which ends with the tail flukes. The head is large, wide and flat. Extending from the lower jaw to the navel are 55- 68 grooves, known as pleats, which expand when feeding, enabling the mouth to hold large volumes of water. The water is then strained through 260-400 fringed plates known as baleen (whalebone). These black plates are roughly 39 inches (97.5 cm) in length, 21 inches (52.5 cm) wide, and weigh 200 lb (90 kg). The baleen filter out food from the water.

The blue whale, due to its massive size, has a massive circulatory system. The heart alone is the size of a Volkswagon Beetle, and weighs 2000 lb (908 kg). The aorta, the largest artery leading from the heart, is large enough for a person to crawl through. Roughly 14 000 lb (6400 kg) of blood is pumped from the heart to the rest of the body.

Blue whales are aquatic mammals, and therefore lack legs (although vestigial limbs can be found internally). However, they have fins, flippers, and flukes, which direct the movement of the whale underwater. The dorsal fin is positioned 3/4 of the way back on the body. It varies in shape but is generally like that of a sickle, and measures 1 ft (30 cm) in height. The flippers are positioned 1/3 of the way back along either side of the body and are generally 8 ft (2.4 m) long. The flippers are tapered. The tail flukes are triangular and are 25 ft (7.6 m) wide.

Blue whales are typically a blue-grey in colour. The flippers are lighter than the body, and the underside of the are flukes darker. The belly is a yellow-green in colour due to microscopic diatoms that are picked up while swimming.

Blue whales are highly communicative, and are perhaps the loudest of all the animals. Their calls can reach 188 decibels and travel hundreds of kilometers underwater.

Blue whales have a life span of 35-50 years.

HABITAT

Blue whales can be found in all the world's oceans, from the Indian to the Arctic. During the winter months they can be found in the tropical ocean waters, and in the summer they head back to arctic or antarctic waters. They migrate because food is less plentiful in the warmer waters than in the colder waters. They rarely travel as far north as the Chukchi Sea, and are almost never seem in the Bering Sea.

Blue whales are not as social as some of the other cetaceans. While they can be found in pods of 50-60 individuals, they generally travel alone or in pairs.

FOOD

The blue whale has a massive body that requires a lot of energy, therefore requiring a lot of food. However, they are selective eaters, feeding primarily on small, 2 inch (5 cm) crustaceans known as krill. It is estimated that an individual blue whale must consume 40 000 000 krill per day to meet its energy requirements.

The blue whale catches most of its food while diving. It can dive to depths of 1650 ft (495 m). As it surfaces, it opens its mouth and expands its pleats. Large volumes of seawater, and hopefully krill, pour into the enlarged cavity; when the mouth closes, the pleats constrict and all the water is forced through the long bristles on the baleen and out the mouth. Any krill in that water are trapped by the bristles and are scooped up by the tongue and swallowed.

ENEMIES

It is estimated that at one time as many as 200 000 blue whales roamed throughout the world's oceans. Due to overhunting by whalers for their oil and blubber, the entire species was almost exterminated. From 1930-31 alone, 30 000 southern blue whales were slaughtered. A ban on whaling blue whales was placed in 1966, and the population has since recovered. However, there are still only 10 000 blue whales alive today. Blue whales are considered to be a threatened species.

The only natural enemy for the blue whales are killer whales. Pods of killer whales have been known to attack and kill juveniles.

BREEDING

Blue whales reach sexual maturity at 6-10 years of age. The mating season occurs in the early spring when they reach the warmer waters. The gestation period is 11-12 months, and the calves are born tail-first. The calf is 25 ft (7.6 m) long at birth, and doubles its length by 7 months. The calf leaves its mother after one year.

Blue whale cows mate every 3 years. Twins are rare, constituting only 1% of total births.

RELATIVES

There are three subspecies of the blue whale: B. m. intermedia (southern blue whale), B. m. musculus (northern blue whale) and B. m. brevicauda (pygmy blue whale Indian Ocean). The blue whale is a baleen whale along with the humpback, minke, fin, sei, and Brydes whales.

RESOURCES CITED

1. "Blue Whale" Funk & Wagnall's Wildlife Encyclopedia, vol 2, pg 244-245, BPC Pub Ltd NY 1974
2. "Blue Whale" Wildlife Fact File, IM Pub Inc, USA
3. www.zoomwhales.com/subjects/whales/species/Bluewhale.shtml
4. www.seaworld.org/animal_bytes/bluewhaleab.html
5. www.state.ak.us/local/akpages/FISH.GAME/notebook/marine/blue.htm
6. mbgnet.mobot.org/salt/whale/blue.htm
7. www.acsonline.org/factpack/bluewhl.htm

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