The Blue Whale

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            The blue whale (Balaenoptera musculus) is a marine mammal belonging to the suborder of baleen whales (called Mysticeti). At 30 metres (98 ft) in length and 180 metric tons (200 short tons) or more in weight, it is the largest known animal to have ever existed. There are at least three distinct subspecies, B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia (Antarctic Blue Whale) of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of small crustaceans known as krill.

Status: The blue whale is classified as Endangered (EN) on the IUCN Red List. It is listed on Appendix I of CITES and Appendix I of the Convention on Migratory Species. Subspecies: Antarctic blue whale, Balaenoptera musculus intermedia, is classified as Critically Endangered (CR); and the pygmy blue whale, Balaenoptera musculus brevicauda, is classified as Data Deficient (DD).

Population: 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 10,000-25,000, corresponding to about 3-11% of the 1911 population size.

Description: The blue whale is the largest animal to have ever lived, being almost as big as a Boeing 737 and even larger than the biggest dinosaurs. The largest recorded length for a blue whale is 33.5 metres, although most individuals vary between 24 and 27 metres. The heart of this monstrous whale is actually around the size of a Volkswagen Beetle.

            Like other rorquals (members of the family Balaenopteridae), the blue whale has a long, somewhat tapered and streamlined body, with the head making up less than one-fourth of its total body length. The rostrum (upper part of the head) is very broad and flat and almost U-shaped, with a single ridge that extends just forward of the blowhole to the tip of the snout. The body is smooth and relatively free of parasites, although a few barnacles may attach to the edge of the tail fluke, the tips of the flippers and to the small, triangular dorsal fin. There is a row of 300 to 400 black baleen plates on each side of the mouth, and approximately 90 throat grooves extend to the navel, which allows the throat to expand enormously during feeding.

            The blow (or spout) of this species is the biggest amongst all whales, the slender upright column of air rising up to nine meters. Blue whales in the Northern Hemisphere are generally smaller than those in the Southern Ocean. The female may be up to 10 metres longer than the male.

            Despite its common name, the blue whale is actually greyish-blue, with a mottled effect that is visible in some lights and can allow individuals to be identified. The underside often has a yellowish tinge, especially on whales living in polar waters, which is caused by microscopic algae called ‘diatoms’ and led to early whalers giving this species the nickname ‘sulphur bottom whale’.

Range: The blue whale is found in every ocean except the Arctic, with a range that extends from the periphery of drift-ice in polar seas to the tropics, although it is absent from some seas such as the Mediterranean, Okhotsk and Bering. It follows a seasonal migration pattern between summering and wintering areas, although some individuals may remain in certain areas year-round. The species’ range can be loosely organised into three main populations: one in the North Atlantic, one in the North Pacific, and another in the southern Hemisphere.


            In the Antarctic region, which formerly supported the largest blue whale population, the blue whale occurs from the Antarctic Polar Front up to and into the ice in the summer, and is thought to migrate equator-wards before winter. In the North Atlantic the summer distribution of the blue whale extends from the Scotian Shelf to the Davis Strait in Canada, eastwards to Iceland, the Denmark Strait and Svalbard, and north to the ice edge. The winter distribution of the blue whale in the North Atlantic is poorly known, but it is thought that in the past the blue whale was widely distributed in the southern half of the North Atlantic in the winter.

            The blue whale occurs in the eastern Pacific from southern Chile to Costa Rica, where it is present year-round. In the North Pacific, it is found from the coast of Oregon to the Kurile Islands and north to the Aleutian Islands. In the past the blue whale was regularly caught off southern Japan and the Korean peninsula, but it has not been seen there in recent years.

Habitat: The blue whale inhabits the open ocean, where it is found most frequently along the continental shelf edge and near polar ice. It feeds at both the surface and at depth, undertaking diurnal vertical migrations as it follows its krill prey to depths of at least 100 metres.

            Poleward movements in the spring allow the blue whale to take advantage of high prey abundances in the summer, while movement towards the subtropics in the autumn allows the blue whale to reduce its energy expenditure while fasting, avoid ice entrapment and breed in warmer waters.

Biology: The blue whale usually occurs alone or in groups of two or three, but occasionally large groups of up to 60 may form in areas of high food abundance. It feeds mainly on shrimp-like krill, which are filtered through the baleen plates. During feeding, large volumes of water and food can be taken into the mouth because the pleated grooves in the throat expand. As the mouth closes, water is expelled through the baleen plates, which trap the food on the inside to be swallowed. During the summer feeding season, the blue whale gorges itself, consuming an astounding 4 tonnes or more each day, meaning it may eat up to 40 million krill a day.

            The blue whale reaches sexual maturity at 7 to 10 years of age, when it will mate with several partners during winter and early spring. A single calf is produced after a gestation period of 10 to 11 months and weaned at the summer feeding grounds, when it is approximately seven months old. During the nursing period, the calf consumes around 100 gallons of the mother’s fat rich-milk and grows an incredible one and a half inches in length each day, with a weight gain of 90 kilograms per day. The inter-birth period for female blue whales is probably two to three years, although this may have decreased recently in response to the low population densities.

            The blue whale produces louder calls than any other animal on earth. Communication occurs via a variety of low frequency sounds and clicks. The male blue whale is capable of producing particularly long calls, which have been well studied and appear to have functions in sensing the environment, prey detection, communication and male display. The call of the blue whale reaches levels up to 188 decibels. This extraordinarily loud whistle can be heard for hundreds of miles underwater. Theoretical calculations by Roger Payne and Douglas Webb (from the 1970's) predicted that the loudest whale sounds might be transmitted across an entire ocean. The blue whale is much louder than a jet, which reaches only 140 decibels.

Threat: Because of its enormous size and speed, the blue whale was largely safe from early whalers, who could not pursue it in open boats with hand harpoons. However, the advent of the exploding harpoon gun in 1868 allowed for the commercial exploitation of this species, with the whaling industry particularly focusing on the blue whale after 1900. The slaughter peaked in 1931, when over 29,000 were killed in one season. After that, blue whales became so scarce that the whalers turned to other species. 

          More than 360,000 blue whales were taken by whaling fleets in the Southern Hemisphere from 1904 to 1967, and the Antarctic and North Atlantic populations were probably depleted to the low hundreds by the time whaling ceased. The total global blue whale population has declined by at least 70 percent, and possibly as much as 90 percent, over the last three generations, with the formerly very large Antarctic population declining over the same period by as much as 97 percent.

            Although commercial whaling of the blue whale is now banned, its population is so small that any further mortalities may severely impact on the survival of the species. It is still subject to a number of threats including ship strikes, noise and chemical pollution, and net entanglement. The remote distribution of some blue whale populations probably makes them less vulnerable to human impacts than some other cetacean species, but local populations that inhabit waters with significant levels of human activity, such as the Gulf of St. Lawrence, may be particularly vulnerable to these threats.

Conservation: Hunting of the blue whale was banned in 1966, although some illegal soviet whaling persisted for several years after. No blue whales have been deliberately caught since 1978. However, this protection almost came too late for the blue whale, and recovery has been extremely slow. Only in the last few years have there been signs that numbers may be increasing. Today, there are an estimated 10,000 to 25,000 blue whales surviving worldwide, which represents around 3 to 11 percent of the total pre-commercial exploitation population. All international trade in the blue whale is further prohibited by its listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) and on Appendix I of the Convention on Migratory Species (CMS or the Bonn Convention).

            The blue whale occurs in a number of Marine Protected Areas throughout its range that is aimed at protecting the whole marine ecosystem, as well as whale sanctuaries in the Antarctic, Indian and Southern Oceans. Several countries have also implemented research and conservation programmes for this species, much of which is coordinated by the International Whaling Commission, and these include identifying areas of critical habitat, investigating species abundance and distribution, and mitigating the threats to the species.




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