Blue whale

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Blue whale as seen from spotter aircraft in the eastern tropical Pacific (1998). Source: NOAA
Species (main)


The Blue whale (scientific name: Balaenoptera musculus), is believed to be the largest animal ever to have existed on the planet, almost as big as a Boeing 737 airplane, and even larger than the greatest dinosaurs. A Blue whale has a body mass of up to 190,000 kilograms (as much as forty African elephants). This exceedingly large marine mammal, in the family of Rorquals (Balaenoptera), part of the order of cetaceans.

Blue whales are also among the fastest swimmers, reaching a speed of 48 kilometres per hour when pursued. The Blue Whale is a baleen whale, meaning that instead of teeth, it has long plates which hang in a row (like the teeth of a comb) from its upper jaws. Baleen plates are strong and flexible; they are made of a protein similar to human fingernails. Baleen plates are broad at the base (gumline) and taper into a fringe which forms a curtain or mat inside the whale's mouth. Baleen whales strain huge volumes of ocean water through their baleen plates to capture food: tons of krill, other zooplankton, crustaceans, and small fish.

This species of whale can eat daily six to seven tons of krill, a small, shrimp-like crustacean, by gulp-feeding. With each mouthful, the whale's throat stretches along a series of grooves, enlarging the mouth’s capacity; then the water is expelled, with the krill remaining, trapped by baleen plates. This species tends to feed at less than 100 metres deep, and make dives lasting between five and twenty minutes. Most Blue whales are thought to spend the summer feeding in the colder waters of high latitudes, migrating to warm waters in the winter where females give birth; however, some may be resident in the same area year round. No feeding occurs within the breeding grounds.

Communication occurs via a variety of low frequency sounds and clicks. The Blue whale's voice is the deepest of any animal's, and their vocalizations carry for many miles underwater, at frequencies below the range of human hearing. This may enable them to communicate across considerable ocean distances, and may be a sonar-like imaging system that helps a whale map its location relative to distant landmasses or deep underwater terrain.

The species can live for 80 to 90 years, and for centuries, Blue whales were safe from humans because of their sheer size; however, whalers on modern ships armed with harpoon guns drove them almost to extinction. They are protected now, but there is no sign yet that they are recovering from over-exploitation.

Blue whales (Balaenoptera musculus) . Source: NOAA National Marine Fisheries Service
Largest and smallest whale (Blue Whale and Hector Dolphine) compared to an average sized human. Source: T. Bjornstad

Conservation Status

IUCN Conservation Status - Endangered.png.jpeg

Scientific Classification

Kingdom: Animalia
Phylum:--- Chordata
Class:------ Mammalia
Order:-------- Cetacea
Family:-------- Balaenopteridae
Genus:--------- Balaenoptera
Species:-------- Balaenoptera musculus (Linnaeus, 1758)

Common Names:
Blue rorqual
Great blue whale
Great northern rorqual
Ostende whale
Pygmy blue whale
Sibbald's rorqual
Sibbald’s rorqual
Sulphur-bottom
Sulphur-bottom whale
Sulphurbottom whale
Blue whale

Blue whales usually occur alone or in groups numbering between two and three individuals, but occasionally large groups of up to 60 individuals may form in areas of high food abundance.

The two main populations (north and south latitudes) remain separated; moreover, the seasons are reversed in the two hemispheres, so that north to south migrations are seasonally reversed..

A single calf is produced after a gestation period of 10 to 11 months. The inter-birth period is two to three years, although this may have decreased recently in response to the reduced population densities. At birth, a calf measures about seven metres in length and may consume up to 50 gallons of milk a day in its first year of life, leading to a weight gain of 90 kilograms per day.

Physical Description

Notable elements of Blue whale morphology include endothermic regulation; Homoiothermic modality; and bilateral body symmetry.

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 very small, only about 35 centimetres, and set far back on the body. The Blue whale has a mottled dorsal and lateral colouration with white under the flippers.

This massive mammal is acturally quite slender bodied, given its size. There is a sexual dimorphism present, with females somewhat exceeding the size of males. The average head-body length in adult males is 25 metres (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)

The head is broad and U-shaped, with the head colouration being symmetrical. The upper jaw is the widest in the genus, and the rostrum is the bluntest.

This species is a baleen whale and can be recognised as such by the plates of baleen (rather than teeth) suspended from the upper jaw and the two blowholes on the upper body. There are 50 to 90 throat grooves (the ventral pleats) that extend from the chin to just beyond the navel, characteristic of rorqual family.

The small flippers are less than one-fifth of the body length, and there is onlya single prominent ridge on the snout. The Blue whale can be confused with the Fin whale, but is distinguished by its broad and U-shaped head, a very small dorsal fin that is set far back on the body, and symmetrical head colouration.

Blue whales are usually found alone or in pairs, although in feeding areas up to a dozen have been seen together. It rarely breeches, and when diving, it will often show the tail flukes. Dives may last up to 30 minutes in duration. (Kinze, 2002).

Behaviour

Key behaviours associated with this species are: migration, natatorial; motile; and generally solitary modality. Most populations of Blue whales are migratory; 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 move back toward the equator during the fall. The northern and southern ocean populations remain disparate and distinct.

Normal swimming speed is approximately 22 kilometres/hour (km/hr), but Blue whales can attain a top speed of 48 km/hr if alarmed. Feeding is usually at depths less than 100 metres; harpooned animals have dived as deep as 500 m. Normal dives last from 10 to 20 minutes and are separated by eight to fifteen blows. The spout of blue whales can reach a vertical extent of 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)

Voice and Sound Production

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

Little is known about intraspecific communication in these whales. Blue whale vision and smell are limited, but hearing is very sensitive, and antropogenic underwater sound may interfere with blue whale communication.(Wilson and Ruff, 1999) Other perception channels include tactile and chemical.

Reproduction

Less is known about mating in the large whale species, than in the case of whales of lesser size. Key reproductive features are:

  • Iteroparous
  • Seasonal breeding
  • Gonochoric/gonochoristic/dioecious (sexes separate)
  • Sexual reproduction
  • Viviparous

Breeding occurs during the winter months, and gestation period is known to be eleven or twelve months long, unusually short for an animal its size. One possible explanation is that longer gestation periods would mean that the young would be born in the season spent in the season spent in cold waters (Ronald Nowak 1999).

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 seven to eight metres long. While nursing, blue whales can gain up to 90 kilograms in body mass per day. Blue whale young are cared for extensively by their mother. Male blue whales do not contribute parental care. (Nowak, 1991; Wilson and Ruff, 1999) Young are weaned after seven or eight months, usually after attaining a length of 16 metres (m).

Sexual maturity occurs at about five years old in females, or at about 21 to 23 m in length and young are produced every two or three years thereafter. Twins are rare, but do occur occassionally. Males mature at 20 to 21 m, just under five years old. Females give birth to young every two to three years.

Lifespan/Longevity

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) The maximum longevity inferred from observations in the wild is 110 years.

Distribution and Movements

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)


The IUCN Redlist of threatened species notes the distribution of several subspecies:

"Antarctic form B. m. intermedia . . . occurs in the Antarctic in summer (Branch et al. 2006). Its winter distribution is poorly known, but the presumption has been that animals migrate in winter to lower latitudes, largely because Blue whales were caught off Namibia, South Africa and Chile in winter (Best 1998, Mackintosh 1965).

Pygmy blue whales (B. m. brevicauda) are confined mainly to the area north of 55°S . . . They are most abundant in the southern Indian Ocean on the Madagascar plateau, and off South Australia and Western Australia, where they form part of a more or less continuous distribution from Tasmania to Indonesia. Blue whales are found year round in the northern and equatorial Indian Ocean, especially around Sri Lanka, and the Maldives, and at least seasonally near the Seychelles and in the Gulf of Aden.

Blue whales occur in the eastern Pacific from around 44°S in southern Chile (Hucke-Gaete et al. 2005) as far as the Costa Rica Dome where they are present year-round (Reilly and Thayer 1990). There may be a gap from there to Baja California where they are quite common as also off the Californian coast (Calambokidis and Barlow 2004) but tracking of a tagged whale suggests that some of the Californian whales may migrate to the Costa Rica Dome in winter (Mate et al. 1999). North of 40°N, blue whales occur across the North Pacific from the coast of Oregon to the Kurile Islands (Russian Federation), and north to the Aleutian Islands (US -Alaska) but not far into the Bering Sea. In the past blue whales were caught off southern Japan and the Korean peninsula, but none have been seen there in recent years.

In the North Atlantic the summer distribution of blue whales extends in the west from the Scotian Shelf to the Davis Strait (Canada) (NMFS 1998). Blue whales occur in the Denmark Strait, around Iceland and north to the ice edge, and in the northeast to Svalbard (Norway). Historically, blue whales were commonly caught along the coasts of North and West Norway, the Faeroes and the NW British Isles. They also occur in low numbers off NW Spain (Bérubé and Aguilar 1998) and in the past near the Strait of Gibraltar, but not in the Mediterranean (Reeves and Notarbartolo di Sciara 2006). The winter distribution is poorly known but it appears that in the past blue whales were widely distributed in the southern half of the North Atlantic in winter (Reeves et al. 2004).

McDonald et al. (2006) use song to suggest nine different groupings of blue whales. They argue that because song is used in mating, that these different song types, five of which have data spanning over 30 years and showing stability, should form the basis for population structure hypotheses. Although some of the geographic locations correspond to IWC stocks, for example the northern Indian Ocean, others do not. Thus, the population structure in this account likely underestimates the true number of discreet groups of blue whales."

Habitat

The Blue whale is an open ocean whale, not often seen near the coast in northwest Europe. It can be found at the surface or diving to a depth as much as 150 metres.

Food and Feeding Habits

The diet of Blue whales is principally krill. In southern waters the main species eaten by way of filter-feeding is Euphausia superba, a small (less than seven centimetre) planktonic crustacean that is extremely abundant. In northern waters the chief prey species are Thysanoessa inermis and Meganyctiphanes norvegica, although other planktonic species and small fish are also taken. Adult Blue whales can ingest three to four tons of krill per day. Animal prey include aquatic crustaceans and zooplankton.

Predation

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 Orca orcinus and large sharks.

Economic Importance for Humans

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, along with other large whales, have an important ecotourism value.

Threats and Conservation Status

Blue whales were not initially among the most heavily hunted species due to their size, speed, and remote habitat. Technological advances from years 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.

The IUCN Redlist of threatened species notes that the "global population of blue whales is uncertain, but based on the above information, the global total for the species is plausibly in the range 10,000 to 25,000, corresponding to roughly three to eleven percent of the 1911 population size."

IUCN Red List classifies the species as Endangered (Antarctic population Critically Endangered). The USA Federal Government lists the Blue whale as Endangered. The Blue whale is covered in CITES: Appendix I.

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Citation

Encyclopedia of Life & Peter Saundry (2011). Blue whale. ed. C. Michael Hogan. Encyclopedia of Earth. National Council for Science and Environment. Washington DC. Retrieved from http://editors.eol.org/eoearth/wiki/Blue_whale
Retrieved from "https://editors.eol.org/eoearth/index.php?title=Blue_whale&oldid=143316"