Blue whale - Wikipedia, the free encyclopedia: The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whales (Mysticeti).[9] At 30 metres (98 ft)[10] in length and 190 tonnes (210 short tons)[11] or more in weight, it is the largest existing animal and the heaviest that has ever existed.[12]
Long and slender, the blue whale's body can be various shades of bluish-grey dorsally and somewhat lighter underneath.[13] There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and 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 small crustaceans known as krill.[14]
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 whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide,[15] located in at least five groups. More recent research into the Pygmy subspecies suggests this may be an underestimate.[16] Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000).[17] 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.[18]
The blue whale is the largest animal ever known to have lived.[33][34] By comparison, one of the largest known dinosaurs of the Mesozoic Era was Argentinosaurus,[35] which is estimated to have weighed up to 90 tonnes (99 short tons), comparable to the average of blue whale.[36] Amphicoelias fragillimus, at an estimated 122 tonnes (134 short tons) is still lighter than the largest blue whales, despite being 200 feet (61 m) in length.[37]
Due to its large size, several organs of the blue whale are the largest in the animal kingdom. A blue whale's tongue weighs around 2.7 tonnes (3.0 short tons)[41] and, when fully expanded, its mouth is large enough to hold up to 90 tonnes (99 short tons) of food and water.[14] Despite the size of its mouth, the dimensions of its throat are such that a blue whale cannot swallow an object wider than a beach ball.[42] Its heart weighs 1,000 pounds (450 kg) and is 6 feet (1.8 m) wide, with a thoracic aorta estimated to be 9 inches (23 cm) in diameter.[43] During the first seven months of its life, a blue whale calf drinks approximately 400 litres (110 US gal) of milk every day. Blue whale calves gain weight quickly, as much as 90 kilograms (200 lb) every 24 hours. Even at birth, they weigh up to 2,700 kilograms (6,000 lb)—the same as a fully grown hippopotamus.[9] Blue whales have relatively small brains, only about 6.92 kilograms (15.26 lb) , about 0.007% of its body weight.[44] The blue whale penis is the largest penis of any living organism[45] and also set the Guinness World Record as the longest of any animal's.[46] The reported average length varies but is usually mentioned to have an average length of 2.4 m (8 ft) to 3.0 m (10 ft).[47]
Scientists estimate that blue whales can live for at least 80 years,[39][60][66] but since individual records do not date back into the whaling era, this will not be known with certainty for many years. The longest recorded study of a single individual is 34 years, in the eastern North Pacific.[67] The whales' only natural predator is the orca.[68] Studies report that as many as 25% of mature blue whales have scars resulting from orca attacks.[39] The mortality rate of such attacks is unknown.
With global warming causing glaciers and permafrost to melt rapidly and allowing a large amount of fresh water to flow into the oceans, there are concerns that if the amount of fresh water in the oceans reaches a critical point, there will be a disruption in the thermohaline circulation.[109] Considering the blue whale's migratory patterns are based on ocean temperature, a disruption in this circulation, which moves warm and cold water around the world, would be likely to have an effect on their migration.[110] The whales summer in the cool, high latitudes, where they feed in krill-abundant waters; they winter in warmer, low latitudes, where they mate and give birth.[111]
The change in ocean temperature would also affect the blue whale's food supply. The warming trend and decreased salinity levels would cause a significant shift in krill location and abundance.[112]
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