The biggest animal in the world
Peng-En Chan
Introduction
The blue whale is a marine mammal belonging to the baleen whales (Mysticeti). At 30 metres (98 ft) in length and 180 tonnes (200 short tons) or more in weight, it is the largest extant animal and is the heaviest known to have existed.
Long and slender, the blue whale's body can be various shades of bluish-grey dorsally and somewhat lighter underneath. There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Oceanand B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Oceanand South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of smallcrustaceans known as krill.
Their diet
Blue whales feed almost exclusively on krill, though they also take small numbers of copepods.An adult blue whale can eat up to 40 million krill in a day.[34] The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms (7,900 lb) of krill in a single day. The daily energy requirement of an adult blue whale is in the region of 1.5 million kilocalories.
Their size
The blue whale is the largest animal ever known to have lived.By comparison, one of the largest known dinosaurs of the Mesozoic Era was Argentinosaurus,which is estimated to have weighed up to 90 tonnes (99 short tons), comparable to the average of blue whale.Amphicoelias fragillimus, at an estimated 122.4 tonnes (134.9 short tons) is still lighter than the largest blue whales, despite being 190 feet (58 m) in length.
Their life history
Mating starts in late autumn and continues to the end of winter.Little is known about mating behaviour or breeding grounds. Females typically give birth once every two to three years at the start of the winter after agestation period of 10 to 12 months.The calf weighs about 2.5 tonnes (2.8 short tons) and is around 7 metres (23 ft) in length. Blue whale calves drink 380–570 litres (100–150 U.S. gallons) of milk a day. Blue whale milk has an energy content of about 18,300 kJ/kg (4,370 kcal/kg). The calf is weaned after six months, by which time it has doubled in length. Sexual maturity is typically reached at five to ten years of age.
Protect the blue whale
Blue whales were abundant in nearly all the oceans on Earth until the beginning of the twentieth century. For over a century, they were hunted almost to extinction by whalersuntil protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, in at least five groups. More recent research into the Pygmy subspecies suggests this may be an overestimate. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000). There remain only much smaller (around 2,000) concentrations in each of the eastern North Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere. As of 2014, the Californian blue whale population has rebounded to nearly its pre-hunting population.