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Blue Whales – The Largest Animal on Earth


Animal Classification

Blue Whale (Balaenoptera musculus)


It is difficult to imagine the size of the blue whale, the largest animal inhabiting the earth. They are about the length of three school buses and the heart alone is the size of a small car. There are records of individuals over 100 feet (30.5 m) long, but 70-90 feet (23-27 m) is probably average. An average weight for an adult is 200,000 to 300,000 pounds (100-150 tons). Blue whales are an overall blue-gray color, mottled with light gray. Cold water diatoms adhere to their skin and sometimes give their bellies a yellowish tinge, giving the blue whale its nickname of "sulfur bottom." Blue whales are long and streamlined. Their dorsal fins are extremely small, and their pectoral flippers are long and thin. Blue whales are rorqual whales, a family of baleen whales with pleated throat grooves that expand when the animal takes in water while feeding. In blue whales, 55-68 throat grooves extend from the throat to the navel. Blue whale baleen is black with over 800 plates.


Blue whales have been found in every ocean of the world, except for the Arctic. Blue whales swim individually or in small groups. Pairs are very commonly seen. Approximately 1,500 blue whales live off the California Coast and migrate to Mexico and Costa Rica.


Females give birth to calves every two to three years. They remain pregnant for about one year before giving birth. When born, the blue whale calf is about 23 feet (7 m) long and weighs 5,000 to 6,000 pounds (2,267 to 2,722 kg). A nursing blue whale mother produces over 50 gallons (200 liters) of milk a day. The milk contains 35 to 50% milk fat and allows the calf to gain weight at a rate of up to 10 pounds an hour or over 250 pounds (113 kg) a day! At six months of age and an average length of over 52 feet (16 m), the calf is weaned. The blue whale reaches sexual maturity between 5-15 years of age.


The favorite food of these giants is krill, or shrimp-like euphausiids, that are up to three inches long. Blue whales can eat up to 6 tons (12,000 pounds) of krill a day during the feeding season! They concentrate on feeding during the polar summers primarily around the Channel Islands, Monterey Bay, and the Farallon Islands/Cordell Bank. During the winter months, they migrate to the warmer waters in Mexico and Costa Rica.


Blue whales are considered an endangered species. The blue whale was too swift and powerful for the 19th century whalers to hunt, but with the arrival of harpoon cannons, they became a much sought after species for their large amounts of blubber. The killing reached a peak in 1931 when 29,649 blue whales were taken. By 1966, blues were so scarce that the International Whaling Commission declared them protected throughout the world. With protection, today, there are between 5,000-10,000 blue whales in the Southern Hemisphere and about 3,000-4,000 blue whales in the Northern Hemisphere. Despite these low numbers, we can still see them in the summer and fall off the central California coast, feeding in such places as the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries. The National Oceanic and Atmospheric Administration (NOAA) estimates more than 1,500 blue whales feed along the California coast, one of the largest gatherings of blue whales globally.

At The Marine Mammal Center

The Marine Mammal Center does not treat blue whales on-site.

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