The largest creature ever known to have existed on Earth is the present-day blue whale. Today's blue whale is even larger than its prehistoric ancestors, reaching a total length of 30 m (100 ft.) and a weight of 136 t (150 tn.). Adult female blue whales are larger than adult males. The blue whale's heart alone is the size of a small car! Even the largest dinosaur weighed only about 18 t (20 tn.), although it probably reached 40 m (131 ft.) in length.
The calves measure 7 m (23 ft.) at birth and weigh about 2.2 to 2.7 t (2.4 to 3 tn.). A female blue whale can produce more than 200 litres (50 gal.) of high-fat milk per day. The calf gains up to 4 kg (9 lb.) per hour. When weaned at about six months of age, the calf will already be about 16 m (52 ft) long.
This giant animal is placid and shy. On the ocean surface, its normal cruising speed is about 12 knots, but it is capable of attaining 20 knots in short bursts. The maximum reported depth reached by the species is 194 fathoms. It is capable of remaining submerged beneath the surface for 50 minutes, although 10 to 15 minutes is more typical.
Blue whales have been found in every ocean of the world: Pacific, Atlantic, Indian, Arctic and Southern.
Blue whales comprised about 90% of the whaling industry's total catch during the early part of the 20th century, after the advent of harpoon cannons. In 1931 alone, almost 30 000 of these majestic creatures were killed. By 1966 there were so few blue whales that the International Whaling Commission declared them protected. In 2000 it was estimated that there were fewer than 10 000 left.