Blue Whale

Blue whales are the largest animals ever to live on our planet. They feed almost exclusively on krill, straining huge volumes of ocean water through their baleen plates (which are like the teeth of a comb). Some of the biggest individuals may eat up to 6 tons of krill in 1 day.

Blue whales are found in all oceans except the Arctic Ocean. There are five currently recognized subspecies of blue whales.

The number of blue whales in the world’s oceans is only a small fraction of what it was before modern commercial whaling significantly reduced their numbers during the early 1900s, but populations are increasing globally. Today, blue whales are listed as endangered under the Endangered Species Act. The primary threats currently facing blue whales are vessel strikes and entanglements in fishing gear.

NOAA Fisheries and its partners are dedicated to conserving and rebuilding blue whales worldwide. We use a variety of innovative techniques to study, protect, and rescue these endangered animals. We engage our partners as we develop regulations and management plans that foster healthy fisheries and reduce the risk of entanglements, create whale-safe shipping practices, and reduce ocean noise. Blue whales have a long body and generally slender shape. Their mottled blue-gray color appears light blue under water—hence their name, the blue whale. The mottling pattern is variable and can be used to identify individuals.

Antarctic blue whales are generally larger than other blue whale subspecies. For example, in the North Atlantic and North Pacific, blue whales can grow up to about 90 feet, but in the Antarctic, they can reach up to about 110 feet and weigh more than 330,000 pounds. Like other baleen whales, female blue whales are somewhat larger than males. Blue whales live in all the world's oceans except the Arctic. They sometimes swim in small groups but usually alone or in pairs. They generally spend summers feeding in polar waters and undertake lengthy migrations towards the Equator as winter arrives.

Blue whales typically cruise the ocean at more than 5 miles an hour but can accelerate to more than 20 miles an hour for short bursts. They are among the loudest animals on the planet, emitting a series of pulses, groans, and moans, and it is thought that in good conditions, blue whales can hear each other up to 1,000 miles away. Scientists think they use these vocalizations not only to communicate and—along with their excellent hearing—to sonar-navigate the dark ocean depths.

The primary and preferred diet of blue whales is krill—tiny shrimp-like animals. Fish and copepods (tiny crustaceans) may occasionally be part of the blue whale’s diet. When these marine mammals hunt for food, they filter feed by swimming toward large schools of krill with their mouth open, then push the water out of their mouth with their tongue while keeping the krill trapped inside their baleen bristles. Blue whales are found in all oceans except the Arctic. They generally migrate seasonally between summer feeding grounds and winter breeding grounds, but some evidence suggests that individuals remain in certain areas year-round. Information about distribution and movement varies with location, and migratory routes are not well-known. In general, distribution is driven largely by food requirements—they occur in waters where krill is concentrated.

In the North Atlantic Ocean, their range extends from the subtropics to the Greenland Sea. Blue whales have been sighted in the waters off eastern Canada, in the shelf waters of the eastern United States, and infrequently in the Gulf of Mexico and the Caribbean.

Along the West Coast of the United States, eastern North Pacific blue whales are believed to spend winters off of Mexico and Central America. They likely feed during summer off the U. S. West Coast and, to a lesser extent, in the Gulf of Alaska and central North Pacific waters.

Blue whales with young calves have been observed often in the Gulf of California from December through March. Thus, at least some calves may be born in or near the Gulf of California; this area is probably an important calving and nursing area for the species.

In the northern Indian Ocean, there is a "resident" population. Blue whale sightings, strandings, and acoustic detections have been reported from the Gulf of Aden, Arabian Sea, and across the Bay of Bengal. The migratory movements of these whales are largely unknown, but may be driven by oceanographic changes associated with monsoons.

In the Southern Hemisphere, Antarctic blue whales occur mainly in relatively high latitude waters south of the "Antarctic Convergence" and close to the ice edge in summer. They generally migrate to middle and low latitudes in winter, although not all whales migrate each year. Pygmy blue whales are typically distributed north of the Antarctic Convergence and are most abundant in waters off Australia, Madagascar, and New Zealand. An unnamed subspecies of blue whale is found in the southeastern Pacific Ocean, particularly in the Chiloense Ecoregion, and migrates to lower latitude areas, including the Galapagos Islands and the eastern tropical Pacific. Blue whales are among Earth's longest-lived animals. Their average lifespan is estimated at around 80 to 90 years. Scientists have discovered that they can closely estimate the animal’s age by counting the layers of a deceased whale's waxlike earplugs, they can get a close estimate of the animal's age.

Scientists know little about the life history of the blue whale. The best available science suggests the gestation period is approximately 10 to 12 months, and that blue whale calves are nursed for about 6 to 7 months. Most reproductive activity, including births and mating, takes place during the winter. Weaning probably occurs on, or en route to, summer feeding areas. The average calving interval is probably 2 to 3 years. The age of sexual maturity is thought to be 5 to 15 years.