Balaenoptera musculus
blue whale

Blue whales are found in all oceans of the world, from the tropics to the drift ice of polar waters. (Nowak, 1991; Wilson and Ruff, 1999)

Blue whales live in the open ocean. (Nowak, 1991; Wilson and Ruff, 1999)

Blue whales are slate to grayish blue and mottled with lighter spots, particularly on the back and shoulders. The undersides often become covered with microorganisms, giving the belly a yellowish tinge. Because of this blue whales are sometimes called "sulphurbottoms". The dorsal fin is short, only about 35 cm. The upper jaw is the widest in the genus, and the rostrum is the bluntest. There are 50-90 throat grooves that extend from the chin to just beyond the navel.

Blue whales are the largest animals ever to exist on earth. Average head-body length in adult males is 25 m; in females it is 27 m. The longest confirmed specimen was 33.5 m in length and the heaviest was 190,000 kg. (Nowak, 1991; Wilson and Ruff, 1999)

Very little is known about mating in the large whale species.

The gestation period is eleven or twelve months long, unusually short for an animal its size. Young are born in warm, low latitude waters in the winter months after the adults return from their high latitude feeding grounds. At birth the young are 7-8 m long. While nursing, blue whales can gain up to 90 kg in body weight a day. Young are weaned after seven or eight months, usually after attaining a length of 16 m. Sexual maturity occurs at about 5 years old in females, or at about 21 to 23 m in length and young are produced every 2 or 3 years after that. Twins are rare but do occur occassionally. Males mature at 20 to 21 m, just under 5 years old. Longevity has been estimated to be as high as 110 years. (Nowak, 1991; Wilson and Ruff, 1999)

Blue whale young are cared for extensively by their mother. Male blue whales do not contribute parental care. (Nowak, 1991; Wilson and Ruff, 1999)

Longevity in blue whales, and other large cetaceans, is estimated by counting the number of ovarian scars in sexually mature females, changes in the coloration of eye lenses, and counting the number of ridges on baleen plates. Age estimates of blue whales suggest a lifespan of 80 to 90 years. (Wilson and Ruff, 1999)

Most populations of blue whales are migratory, though some animals do not migrate. Migrators typically spend the winter in low latitude waters, move towards the poles during the spring, feed in high latitude waters during the summer and head back toward the equator during the fall. There are northern and southern ocean populations that remain distinct. Normal swimming speed is around 22 km/hr, but blue whales can make 48 km/hr if alarmed. Feeding is usually at depths less than 100 m; harpooned animals have dived as deep as 500 m. Normal dives last from 10-20 minutes and are separated by 8-15 blows. The spout of blue whales can reach almost 10 m. Aggregations of up to 60 animals have been reported, but solitary animals or pods of two or three are more common. (Wilson and Ruff, 1999)

Blue whales have the lowest voices of any whale, vocalizing as low as 14 Hz at volumes up to 200 decibels. Sounds at this frequency and intensity can travel for thousands of miles in the deep ocean. These sounds may be used to communicate with other whales. Low frequency pulses may be used to navigate by creating a sonic image of distant oceanic features.

Little is known about intraspecific communication in these whales. Vision and smell are limited, but hearing is sensitive. (Wilson and Ruff, 1999)

The diet of blue whales is principally krill. In southern waters the main species eaten is Euphausia superba, a small (less than 7 cm) planktonic crustacean that is tremendously abundant. In northern waters the main species are Thysanoessa inermis and Meganyctiphanes norvegica, though other planktonic species and small fish are also eaten. Adult whales can ingest 3 to 4 tons of krill per day.

Blue whales, by virtue of their extreme size, have virtually no natural predators. They were hunted by humans extensively in the 20th century, almost to extinction. Blue whale calves may be vulnerable to predation by orcas and large sharks.

Blue whales, and other large baleen whales, are important predators of krill.

Blue whales were formerly heavily hunted for blubber and oil. Because of the immensity of blue whales, only sperm whales approached them in economic importance. A single blue whale could yield 70 or 80 barrels of oil. Baleen was also an important whale product, valued for its plastic like properties that were applied in a wide variety of products.

Blue whales, and other large whales, have important ecotourism value.

There are no negative impacts of blue whales on humans.

Blue whales were not initially among the most heavily hunted species due to their size, speed, and remote habitat. Technological advances from 1860-1920, however, allowed whalers to pursue the species. The estimated total kill of blue whales in the 20th century was 350,000 animals. By the 1960's, blue whales were on the edge of extinction. Despite the opposition of the whaling industry, blue whales gained protection after the 1965/66 whaling season. Estimates of the remaining population range from 2,000 to 6,000 individuals and it is not yet clear that the blue whale will escape extinction. Southern hemisphere populations have been surveyed extensively and are estimated at 400 to 1,400 animals. Northern hemisphere populations are estimated at about 5,000 individuals but the scientific rigor of these surveys has been criticized.