Blue whale is considered to be the largest mammal in the universe because it weights more than 170 tonnes and is up to 100 ft long. Though it lives in water but because it gives birth to child rather than laying eggs it is considered a mammal.
Blue whales are found in Indian Ocean, North Atlantic and Southern ocean. There are different types of blue whales with different shades. Before 20th century they were found in almost all oceans with large quantities but because of extensive hunting their numbers reduced.
Today it is estimated by UN that blue whale population is around 10,000, which is only 1% of the pre-hunting population. Only in Antarctica there were more than 239,000 blue whales before the start of hunting.
As whales are the largest mammal they have no natural threat except from human and environment population. Though one kind of dolphins known as ‘orca’ have been found to attack whales. They are the only type of dolphins with teeth.