The largest creature ever known to have existed on Earth is the present-day blue whale, and may reach a total length of 33 m and a weight of 145 tons. 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. The life span of a blue whale is about 30 years. The calves measure 7 m at birth and weigh about 2 tons. By the time they are a year old, the youngsters measure 18 m. Blue whales comprised about 90 percent of the whaling industry’s total catch during the early part of the last century. In 1931 alone, more than 30,000 of these were killed. Since then, the blue whale population has declined and was on the brink of extinction. Today about 11,000 are suspected to exist.