Blue whale

Name and taxonomy

Carl Linnaeus named the species in Systema Naturae. Balaenoptera means winged whale, and musculus can mean muscle or little mouse, which may have been a joke. Robert Sibbald published one of the first descriptions after a whale stranded in the Firth of Forth in 1692. For that reason the animal was long called Sibbald's rorqual. The English name comes from the Norwegian blåhval, coined by the whaler Svend Foyn, and G. O. Sars adopted it in 1874. Whalers also called it the sulphur bottom, because diatoms tint the belly of some animals yellow.

Four subspecies are recognised. B. m. musculus lives in the North Atlantic and North Pacific, and B. m. intermedia around Antarctica. The pygmy blue whale, B. m. brevicauda, lives in the Indian Ocean and South Pacific, while B. m. indica stays in the northern Indian Ocean. Whales off Chile differ in genes and song and may be a fifth subspecies. A 2024 genomic study backed the Antarctic and Indo-western Pacific forms but not a separate eastern Pacific one.

Evolution and relatives

The blue whale belongs to the order Artiodactyla, which makes the hippopotamus its closest living relative on land. A 2018 analysis dated the split of the rorqual family from other whales to between 10.48 and 4.98 million years ago. The oldest fossil of a modern blue whale is a partial skull from southern Italy, about 1.5 to 1.25 million years old. Genome sequencing places the sei whale as its nearest relative, with the grey whale as a sister group.

Blue whales interbreed with fin whales, and the hybrids can be fertile. A pregnant hybrid caught off Iceland in 1986 had a blue whale mother, a fin whale father and a fetus sired by a blue whale. A 2024 study found about 3.5 percent of the North Atlantic blue whale genome came from fin whales. Gene flow runs one way, from fin whales into blue whales. The Australian pygmy blue whale split off during the last glacial maximum, so its genetic diversity is low.

Appearance

The blue whale has a slender body, a broad U-shaped head and long thin flippers. A small sickle-shaped dorsal fin sits close to the tail, and the flukes are wide and thin. The upper jaw carries 70 to 400 black baleen plates under a metre long. The throat has 60 to 88 grooves that let the mouth expand during a lunge. Two blowholes throw a spout 9.1 to 12 metres high.

An adult measures 21 to 27 metres, and females are larger than males. Mature females average 22 metres in the eastern North Pacific and 25.4 to 26.6 metres in the Antarctic. Average weight runs from 72 to 135 tonnes. Antarctic females average 130 tonnes. The record female, caught in 1947, measured 27.6 m and weighed 190 tonnes. The longest whale measured with care was 29.9 m, and models suggest 33 m is the physical limit.

The heart of one stranded whale weighed 180 kilograms, the largest known. The brain of one 50.9-tonne whale weighed about 3.636 kilograms. The skin is mottled grey-blue, paler below, and the pattern near the dorsal fin identifies individuals. A few albino whales are pure white.

Habitat and range

Blue whales live in all the world's oceans, from the tropics to the edge of the polar ice. They are mostly absent from the Arctic Ocean, the Mediterranean, the Sea of Okhotsk and the Bering Sea. Most populations migrate: they feed near the poles in summer and breed in warmer water in winter. Some whales stay in one area all year, and in some places only part of the population moves. GBIF holds records from 71 countries, which reflects the species' global range.

North Atlantic whales summer from New England to Greenland, especially the Gulf of St Lawrence, and winter towards the West Indies and Azores. Eastern North Pacific whales feed off California in summer and autumn and move to the Gulf of California and the Costa Rica Dome in winter. Pygmy blue whales winter off Indonesia and feed off Western Australia, at Perth Canyon and the Great Australian Bight. Whales are present around New Zealand all year.

Feeding dives average about 201 metres and 9.8 minutes off California. The deepest dive recorded from a tagged blue whale was 315 metres, and 506 m for a pygmy blue whale.

Diet and feeding

The diet is almost entirely krill. Antarctic whales eat Euphausia superba, California whales mostly Thysanoessa spinifera, and pygmy whales Nyctiphanes australis. The northern Indian Ocean subspecies is the exception: it eats mainly sergestid shrimp and dives deeper and longer to do so. Fish, amphipods, squid and jellyfish turn up in droppings as well.

The whale lunges at a krill swarm with its mouth open up to 80 degrees and takes in up to 220 tonnes of water. Throat pouch and tongue then force the water out through the baleen, and the krill stays behind. Whales sometimes roll through 180 degrees during a lunge, perhaps to find the densest patch. A lunge only pays when krill density passes 100 animals per cubic metre. One mouthful can return up to 240 times the energy the lunge costs.

An average blue whale needs about 1,120 kilograms of krill a day, and eats about 4 tonnes. A pregnant female eats about 4 percent of her body weight daily and gains 60 percent of her weight over a summer. Different baleen whales in the Southern Ocean take krill of different sizes, which lessens competition. The whale seems to remember good feeding areas from year to year.

Behaviour and social life

The blue whale is usually alone or in a pair. Where food is dense, gatherings of more than 50 form, and up to 60 have been reported. There is no lasting social structure beyond mother and calf. Groups feed loosely together and break up again.

Cruising speed is 2 to 8 kilometres per hour. Alarmed whales reach 32 to 48 km/h in bursts. The best estimate of top speed is about 27 km/h in racing mode, and satellite tags have recorded 19 km/h. The whale is too heavy to breach like a humpback. A dive normally lasts 10 to 20 minutes, followed by 8 to 15 blows at the surface. The longest dive measured was 15.2 minutes, and the heart can slow to 2 beats a minute at depth.

Communication and senses

Blue whales make some of the loudest and lowest sounds of any animal. The fundamental frequency runs from 8 to 25 hertz, below the range most people can hear, and calls reach 188 decibels. ADW gives a low of 14 Hz and a peak near 200 dB. Such sounds travel for thousands of kilometres through deep water. The inner ear is adapted to low frequencies, while sight and smell are limited.

Songs differ between populations. Eastern North Pacific males repeat pulsed A calls and tonal B calls, which suggests a breeding function. D calls come from both sexes while feeding and from males competing for mates. Songs in the eastern North Pacific dropped in pitch by 31 percent between the early 1960s and the early 2000s. One idea links the fall to recovering numbers and sexual selection for bigger bodies, and another calls it a cultural fashion. During a marine heatwave off California, whales called less often, probably because they had to spend more time hunting food.

Reproduction and life cycle

Blue whales mature at 5 to 15 years, females at about 10 and males at about 12. In the north, females mature at 21 to 23 metres and males at 20 to 21 m. Little is known of mating, but the species seems polygynous: a male trails a female and fights off rivals. Mating runs from autumn to winter.

Gestation lasts 10 to 12 months. A calf is born 6 to 7 metres long and weighs 2 to 3 tonnes. The mother produces about 220 kilograms of milk a day, and the calf gains about 90 kg daily. It is weaned at 6 to 8 months, when it is about 16 metres long. The first film of a nursing calf was taken in New Zealand in 2016.

Calves come every two to three years, and 2.6 years on average in pygmy blue whales. Age is read from the ear plug, which lays down a light and a dark layer each year. Blue whales live about 80 to 90 years, and the oldest found this way was 110. Physical growth stops at about 35 years.

Predators and threats

No natural predator of the adult blue whale is well documented. Orcas attack calves and, rarely, adults. The first recorded attack, off Baja California in 1977, ended when the whale escaped after five hours. Off Western Australia orcas killed blue whales in 2019 and 2021, the first attacks seen directly. Rake scars from orca teeth mark 3.7 percent of blue whales off southeastern Australia and 42.1 percent of pygmy whales off the west.

Ship strikes are the leading cause of death today off the United States west coast, with 17 whales killed from 1998 to 2019. Sri Lankan waters cross one of the busiest shipping lanes, and strikes killed eleven blue whales in 2010 and 2012. Fishing gear entangles a few, and the first case in the United States was reported in 2015. Shipping noise and naval sonar interrupt deep feeding dives. The whale feeds low on the food chain, so pollutants build up less than in top predators, though earwax still shows pesticides and mercury.

Population and conservation

The IUCN listed the blue whale as Endangered in 2018. The global population was 10,000 to 25,000 animals in 2015 to 2018, with 5,000 to 15,000 mature. In 1926 there were at least 140,000 mature whales. The Antarctic holds 5,000 to 8,000, the North Pacific 3,000 to 5,000 and the North Atlantic 1,000 to 3,000. The Antarctic subspecies is Critically Endangered, and iNaturalist lists a Near Threatened rating for Europe.

Whaling peaked in 1930 and 1931, when 30,000 were taken. Antarctic whalers took 350,000 to 360,000 before 1950. Protection came in stages: the Southern Hemisphere in 1939, the North Atlantic in 1955, then Antarctic waters in 1965 and North Pacific waters in 1966. In 1966 the International Whaling Commission ended every blue whale hunt, though the Soviet Union kept killing them into the 1970s.

The species sits on CITES Appendix I and on the Convention on Migratory Species. The United States lists it under the Endangered Species Act. Numbers have very likely grown over recent decades. Slower ships, moved shipping lanes and seasonal closures are the main tools against strikes.

Relationship with humans

Icelanders hunted whales from the 9th century, and more than half of 124 bones from old sites were blue whale. Size and speed kept the blue whale safe from most whalers until the harpoon gun arrived in the mid 19th century. A single whale gave 70 or 80 barrels of oil, and baleen was prized for its springy, plastic-like quality. Only the sperm whale rivalled it in value.

An Icelandic company killed a blue-fin hybrid in 2018, and blue whale meat trade is illegal. Hybrid meat has also turned up in Japanese markets. Today whale watching gives the species real economic value. Research uses earwax, photographs of fin mottling and satellite tags.

The blue whale has no negative effect on people. It has become a symbol of the whaling era and of the case for protecting the sea.

In culture and myth

Whales feature in the myths of seafaring peoples, and the blue whale, as the largest, stands for the ocean itself. Herman Melville mentions the sulphur bottom whale in Moby-Dick. For two centuries naturalists called it Sibbald's rorqual after the Scottish doctor who described one in 1692. The Norwegian name blåhval came from the whaler Svend Foyn, whose harpoon gun made hunting it possible.

In the modern conservation movement the blue whale is the emblem of what whaling nearly destroyed. Its songs, which have dropped in pitch for decades, have become a research puzzle and a popular story. The 1947 record whale and the 29.9-metre Panama Canal specimen anchor every claim that it is the largest animal ever. Museums hang full skeletons and models, and a fetus preserved since 1922 is still used for teaching.