The Blue Whale (Balaenoptera musculus) is a marine mammal belonging to order Cetacea which has the distinction of being the largest animal ever lived on earth, larger than the largest dinosaur. They are not predators like orca whales but feed on planktonic crustaceans, for which they travel thousands of kilometres across oceans often cruising at 50 km/hour.
The longevity of blue whale is believed to be around 80 years although most of them die much earlier, often due to attacks by killer whales. Whales rely on their thick layers of blubber to keep them warm in cold waters of Arctic and Antarctic seas. Whales don’t sleep like other animals but take short naps, floating near the surface of sea. They are called blue whales owing to blue colour of their body on the dorsal side. They are also called sulphur bottom whales because of their yellow underbelly.
SIZE
The Blue Whale is believed to be the largest animal ever lived on earth. Females are larger, measuring about 110 ft. and weighing nearly 180 tonnes. The largest dinosaur attained a length of about 22 m and weighed about 36 tons. A Blue Whale’s tongue weighs around 2.7 tonnes and it is so large that 50 persons can stand on it. Its oral cavity is so large that it can hold up to 90 tonnes of food and water at a time. But its oesophagus is so narrow that it cannot swallow an object larger than a beach ball.
Heart of whale is largest of any animal, the size of a small car. It weighs about 600 kg and 6 adult humans can sit inside it. A Blue Whale’s aorta is about 23 cm in diameter, wide enough for an average human to crawl through it. Its lung capacity is about 5,000 litres. During dives the lungs collapse due to oblique diaphragm and air is stored in a large nasal chamber in the skull. Blue whales nostrils are in the form of twin blowholes on top of the head through which it breathes air and exhales it in the form of a spout that can go as much as 30 feet high from the sea surface.
FEEDING
Whale’s oral cavity is enormous, with around 300 baleen plates hanging from the roof, each of which is about one metre long. Blue Whales feed on small planktons which include mostly crustaceans called krills which they need to consume up to 6 tons in a single day. In numbers this quantity amounts to 40 million krills. Blue whales can dive up to 50 minutes in search of food. They produce a circular trap of bubbles to gather krills to a small area and then trap them in their huge oral cavity. The water is drained out through the parallel baleen plates and krills are trapped inside, which are then swallowed through the narrow oesophagus at leisure.
JUVENILES
The calf of blue whale when born is about 7 metre in length and weighs about 2.5 tonnes. It can drink about 500 litres of milk in a day and grows quickly adding about 90 kg of weight each day. Within a year it grows to 18 m length and starts feeding on krills. Calves always swim close to their mother; otherwise they are hunted by the killer whales.
WHALE HUNTING
Blue whales were rampantly hunted during 20th century so much so that in a single year more than 30,000 whales were killed using advanced exploding harpoon guns. A single whale yielded about 120 barrels of oil from its blubber, which was the primary cause of their hunting. The whaling industry began large scale hunting of blue whales after 1900 when advanced weapons and trawlers were available to hunt such a large animal. The rampant slaughter of whales peaked in 1931 when over 29,000 animals were killed in a single season. This declined their population sharply in a short time. Now, International Whaling Commission has declared them endangered and protected species. Today fewer than 10,000 of these giant creatures are left in the oceans of the world.
WHALE EVOLUTION
Whales belong to order Cetacea of mammals that also includes dolphins, porpoises and killer whales. They evolved 45 million years ago from a group of carnivorous ungulates called Mesonychids that took to aquatic mode of life in order to feed on fish, crustaceans and other animals. Slowly their limbs turned into flippers, hind limbs were lost and a horizontal tail fluke evolved to act as propeller. Unlike fishes, the tail of whales moves up and down rather than side to side. This is because the body of a mammal bends up and down and not sideways as in fishes and reptiles. Whale’s oral cavity changed for trapping krills; teeth were lost and baleen plates appeared. But in killer whales, porpoises and dolphins sharp teeth persisted to feed on fish and other animals.