But food in the tropics is scarce, so the whales depend heavily on their thick layer of blubber for nourishment. In the Antarctic, blue whales feed on vast quantities of a plankton called krill. In Arctic water, they feed on only three species of crustacean plankton. In spite of its bulk, the blue whale can reach speeds of 10 to 15 knots, however, it catches most of its food by diving. It can dive to depths of 1,650 feet and lie submerged for up to two hours.
Blue whales form close ties with one another and are often seen in groups of two or four.
Mating takes place in the warm waters of the tropics, where the young are born. The mother gives birth to a single calf with the assistance of other females, who help her deliver the calf and then nudge the newborn to the surface, where it takes its first breath of air. At birth, the calf measures about 23 feet long and weighs 16,000 pounds. The baby is suckled in the water, drinking more than 160 gallons of milk a day. At 7 months old, it is able to catch its own food.