Blue whales are the largest animals on Earth. They have astounding body parts—tongues that weigh two tons, a heart as large as a small car and skin-folds that extend from beneath the tips of their lower jaws to their navels. When expanded, these folds increase the interior of a blue whale's mouth to the size of a train's box car. Blue whales can grow to 100 feet (30 m) in length and weigh as much as 150 tons—the weight of 30 elephants.
Instead of teeth, blue whales have 300 to 400 fringed baleen plates that hang from their upper jaws and strain their food. Blue whales strain and eat krill, a tiny, shrimplike invertebrate. A whale gulps a mouthful of water and krill, closes its mouth, pushes out the water with its tongue and then swallows its catch of krill. A blue whale's esophagus is only four inches (10 cm) in diameter—so swallowing large fishes isn't possible.
Blue whales visit Monterey Bay during the summer and fall. They come to eat, gulping tons of shrimplike krill. As their common name suggests, blue whales' upper bodies are blue-gray. Their bellies are whitish to yellow. In Arctic or Antarctic waters, yellow diatoms (microscopic algae) often stick to blue whales' underbodies, giving them a nickname of "sulfur bottom."
Whalers began hunting blue whales in earnest after the invention of harpoon guns. The pre-whaling population of blue whales quickly fell from an estimated 350,000 to 1,000 in the mid-1920s. Blue whales became so scarce that in 1966 the International Whaling Commission belatedly declared blue whales a protected species worldwide. The Endangered Species Act also protects blue whales.
Scientists estimate the present population worldwide to be 15,000 whales, with 2,000 of these living in California coastal waters, including Monterey Bay. This is the largest concentration of blue whales in the world. In the summer, whale watchers often see blue whales near the canyon that crosses Monterey Bay.
Calves nurse for seven to eight months, drinking 100 gallons of milk daily. They can gain nine pounds (4 kg) each hour and grow 1.5 inches (3.8 cm) each day.
On July 15, 2004, researchers for the first time in 30 years confirmed a sighting of blue whales in Alaskan waters. They identified one male that had been previously photographed in California, which seems to indicate that the population is increasing and moving back to its traditional feeding grounds.
During the summer, blue whales feed in cold waters near Antarctica and the Arctic, where krill is plentiful. In winter, they migrate to warmer waters for calving. Since krill is scarce or nonexistent in warm waters, the whales live off reserves of body fat until they can feed again.
Some people call whales "swimming oil tankers" because of the use of their blubber as their food supply during their non-eating months.