Blue whale

• 1. Introduction

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  The blue whale, Balaenoptera musculus, has a heart that weighed 180 kilograms in one stranded North Atlantic animal. No other creature has been found with a heavier one. That heart belongs to a baleen whale of the rorqual family Balaenopteridae, a filter feeder with a long, slender body.

  Such an organ raises questions. How long can a blue whale truly grow, and who has tried to prove it? How does a body this vast run on a diet of tiny drifting prey? What do its voices carry across open water? And why is an animal this immense listed among endangered species?

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• 2. Measuring A Giant

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  The longest blue whale ever measured by scientists ran between 29.9 and 30.5 meters from snout tip to tail notch. Females are the larger sex. Whaling records push the figures higher. The International Whaling Commission database lists 88 individuals longer than 30 meters, including one of 33 meters. The longest length on file is 33.6 meters, and the Discovery Committee reported lengths up to 102 feet. Hydrodynamic models suggest that metabolic and energy limits would stop a blue whale growing past 33 meters. The existence of animals beyond 30.5 meters has also been questioned.

  A female caught in the Southern Ocean on the 20th of March 1947 holds the weight record. She measured 27.6 meters and weighed 190 tonnes, with estimates running as high as 199 tonnes. Averages are lower. An adult typically weighs between 72 and 135 tonnes. In the Northern Hemisphere males average 100 tonnes and females 112. Antarctic males average 112 tonnes and Antarctic females 130.

  In 2024, Motani and Pyenson gathered published size records and used regression and volume analyses to link length to mass. They estimated that a 25 meter whale weighs roughly 101-119 tonnes. At 30 meters the estimate rises to 184-205 tonnes. For a 33 meter animal it reaches 252-273 tonnes. A 2025 study by Paul and Larramendi agreed that blue whales could pass 200 tonnes, though probably by less than Motani and Pyenson proposed.

  Perucetus, an ancient whale, is one proposed rival. In some estimates it had a mean weight of 180 tonnes, but studies in 2024 disputed that size. Certain shastasaurid ichthyosaurs have also been suggested as contenders. On land, the sauropod Bruhathkayosaurus has a mean estimate of 110-170 tons, and 240 tons at its most generous. Another sauropod, Maraapunisaurus, is put at 80-120 tons. All of these figures rest on fragmentary remains. The sauropod specimens had even disintegrated before anyone could estimate their size.

  Inside that bulk, the brain of a blue whale weighing 50.9 tonnes came to only about 3.636 kilograms.

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• 3. Names And Kin

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  In 1692, Robert Sibbald found a stranded whale in the estuary of the Firth of Forth in Scotland. His account in Phalainologia Nova is one of the first published descriptions of a blue whale. The animal was later called Sibbald's rorqual in his honour.

  Carl Linnaeus gave the species its scientific name in Systema Naturae. Balaenoptera means winged whale. The second word, musculus, can mean muscle or a diminutive form of mouse, and may have been a pun by Linnaeus.

  The Norwegian word blåhval gave the animal its common name. Svend Foyn coined it shortly after he perfected the harpoon gun, and the Norwegian scientist G. O. Sars adopted it in 1874. Whalers had their own label, sulphur bottom. Some bellies carry a yellow tinge from a coating of huge numbers of diatoms. Herman Melville mentions sulphur bottom whales briefly in his novel Moby-Dick.

  A 2018 analysis suggests the rorqual family split from other whale families between 10.48 and 4.98 million years ago, in the late Miocene. The oldest anatomically modern blue whale found so far is a partial skull from southern Italy. It dates to the Early Pleistocene, roughly 1.5-1.25 million years ago. Whole genome sequencing places the sei whale as the closest relative, with gray whales as a sister group. The same work found gene flow between minke whales and the ancestors of the blue and sei whales. The Australian pygmy blue whale diverged during the Last Glacial Maximum. That recent split left the subspecies with low genetic diversity, and New Zealand blue whales have even less.

  A whale captured off northwestern Spain in 1984 turned out to have a blue whale mother and a fin whale father. An earlier North Pacific catch, a 20 meter anomalous female, showed features of both species. Two live hybrids have since been documented, one in the Gulf of St. Lawrence in Canada and one in the Azores in Portugal. A 70 foot pregnant female caught off Iceland in 1986 had a blue whale mother and a fin whale father. Her fetus, however, was sired by a blue whale, which shows that these hybrids can be fertile.

  A 2024 genome analysis of North Atlantic blue whales found that about 3.5 percent of their genome came from fin whales. The gene flow ran in one direction only, from fin whales to blue whales. It began after the northern and southern populations separated. Fin whales are smaller but match blue whales in cruising and sprinting speed. That would let fin males finish a courtship chase with blue females.

  In July 2018, the Icelandic whaling company Hvalur hf. killed a blue whale. DNA tests in Iceland found it was the offspring of a male fin whale and a female blue whale, though independent testing of the samples was still pending. The International Whaling Commission classes blue whales as a Protection Stock. Trading their meat is therefore illegal, and a kill must be reported. Hybrids have also been detected in whale meat samples from Japanese markets.

  One more reported cross comes from the South Pacific, where marine biologist Michael Poole is credited with a reference to a humpback-blue whale hybrid.

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• 4. Ocean Populations

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  Blue whales have a worldwide distribution, but they are mostly absent from the Arctic Ocean and from the Mediterranean, Okhotsk and Bering Seas. Many populations migrate between summer feeding areas near the poles and winter breeding grounds near the tropics. Others stay put year-round, and some migrate only in part, by age or sex. The animals appear to use memory to find the best feeding areas. Four subspecies are recognized. B. m. musculus lives in the North Atlantic and North Pacific, and B. m. intermedia in the Southern Ocean. The pygmy blue whale, B. m. brevicauda, ranges across the Indian Ocean and South Pacific, and B. m. indica lives in the Northern Indian Ocean.

  In the North Atlantic, summer sightings run from New England along eastern Canada to Greenland, especially in the Gulf of St. Lawrence. Some individuals stay there all year. Whales also gather near Iceland and have become more common in the Norwegian Sea. Others are reported to travel south to the West Indies, the Azores and northwest Africa.

  Off California, Eastern North Pacific blue whales feed from summer into fall. Later in the fall they move to Oregon, Washington State, the Alaska Gyre and the Aleutian Islands. In winter and spring they head south to Mexican waters, mostly the Gulf of California, and to the Costa Rica Dome, where they both feed and breed. Farther west, a central and western Pacific stock summers around the Kamchatka Peninsula and has been recorded wintering in Hawaiian waters.

  The Northern Indian Ocean subspecies stays year-round in the northwestern Indian Ocean. A few individuals have traveled to the Crozet Islands. Among pygmy blue whales, the Madagascar population migrates between the Seychelles and Amirante Islands in the north and the Crozet and Prince Edward Islands in the south. On the way they pass through the Mozambique Channel. Another pygmy group appears to winter off Indonesia and summer off Western Australia, with major concentrations at Perth Canyon. A third may spend winter in the Tasman Sea and the Lau Basin, then feed in the South Taranaki Bight off New Zealand. Antarctic blue whales roam as far north as the Eastern Tropical Pacific, the central Indian Ocean, and the waters of southwestern Australia and northern New Zealand.

  A 2024 genomic study of the global population backed subspecies status for Antarctic and Indo-western Pacific blue whales, but not for eastern Pacific ones. For the Antarctic it reported "no divergence within the Antarctic".

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• 5. Feeding And Growing Up

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  An average blue whale eats about 4 tonnes of krill each day. It gets there by lunge feeding: swimming at a patch of krill at high speed with the mouth open as wide as 80 degrees. One gulp can take in 220 tonnes of water. The whale squeezes the water back out through its baleen plates using pressure from the throat pouch and tongue, then swallows the krill left behind. The upper jaw carries 70-400 black baleen plates, each under a meter long. The throat has 60-88 grooves that let the skin expand. Blue whales have been recorded rolling 180 degrees mid-lunge, which may help them scan the prey field for the densest patches.

  A patch must hold more than 100 krill per cubic meter to repay the cost of a lunge. One mouthful can deliver between 34,776 and 1,912,680 kilojoules, up to 240 times the energy a lunge burns. Whales therefore pick the thickest patches and lunge more often while inside them. A separate estimate puts the daily need of an average whale at about 1,120 kilograms of krill. The surplus is stored for migration and reproduction.

  In the Southern Ocean, blue whales feed on Antarctic krill, Euphausia superba. Pygmy blue whales off South Australia take Nyctiphanes australis. In California the main prey is Thysanoessa spinifera, with North Pacific krill, Euphausia pacifica, less often. The Northern Indian Ocean subspecies instead feeds mostly on sergestid shrimp. To reach them it dives deeper and longer than blue whales elsewhere, averaging 10.7 minutes, to a hypothesized depth of about 300 meters. Fecal analysis also found fish, amphipods, cephalopods and jellyfish in its diet.

  Eastern North Pacific whales diving for krill average 201 meters in depth and 9.8 minutes in length. The deepest dive from a tagged blue whale reached 315 meters, and a pygmy blue whale confirmed a dive to 506 meters. The longest dive measured was 15.2 minutes, well short of a theoretical aerobic limit of 31.2 minutes. At depth the heart rate can fall to 2 beats per minute, then climb to 37 on surfacing. Cruising speed is usually 2-8 kilometers per hour. Bursts of 32-48 kilometers per hour come during encounters with boats, predators or other whales.

  Females reach sexual maturity at an average of about 10 years, and males at about 12. Males appear to compete for females, trailing one and fighting off rivals. Mating takes place from fall to winter. Pregnant females eat roughly four percent of their body weight daily. Gestation may last 10-12 months. A calf is 6-7 meters long and weighs 2-3 tonnes at birth. It gains about 90 kilograms a day on milk that may total 220 kilograms daily. The first video of a calf thought to be nursing was filmed in New Zealand in 2016. Weaning comes at 6-8 months, when the calf is about 53 feet long. Mothers and calves are rarely seen together, perhaps because birth and weaning happen between the whales' arrival at and departure from their summer feeding grounds.

  The youngest blue whale specimen on record is a fetus about 133 millimeters long, collected in 1922 by Messrs. Irvin and Johnson during the harvest of a female. Adults live around 80-90 years or more. Scientists estimate age from the earwax plug, which lays down a light and dark layer each year. The oldest whale aged this way was 110 years old.

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• 6. Voices In The Deep

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  At up to 188 decibels, a blue whale call is among the loudest sounds any animal makes. Its pitch, with a fundamental frequency between 8 and 25 hertz, is among the lowest. The inner ear appears well adapted for hearing such low sounds. Songs vary from population to population.

  The Eastern North Pacific population has been studied most closely. It produces pulsed "A" calls and tonal "B" calls, upswept "C" tones that come before B calls, and separate downswept "D" tones. Only males sing A and B calls, often in repeated sequences, which suggests a role in reproduction. D calls are made by both sexes during social interactions while feeding, and by males competing for mates.

  Off Sri Lanka, blue whales sing a phrase of three units. The first is a pulsive call between 19.8 and 43.5 hertz, lasting about 18 seconds. The second is a frequency-modulated upsweep from 55.9 to 72.4 hertz, lasting about 14 seconds. The last is a tone near 105 hertz that runs about 28 seconds. A whale recorded off Madagascar sang a two-unit phrase instead. It began with 5-7 pulses centered near 35 hertz, followed by a 35 hertz tone lasting about 11 seconds. In the Southern Ocean, an 18-second call opens with a 9-second tone at 27 hertz. It then falls in a 1-second downsweep to 19 hertz and slides on to 18 hertz.

  The pitch of some songs has been sinking. From the early 1960s to the early 21st century, the calls of Eastern North Pacific blue whales dropped in frequency by 31 percent. Pygmy blue whales in the Antarctic have lost a few tenths of a hertz every year since 2002. One idea ties this to recovery from whaling, since a lower pitch signals a larger body and may be favored by sexual selection. A June 2022 study suggested the decline is simply a cultural phenomenon.

  A February 2025 study drew on more than six years of acoustic monitoring off California. During a heatwave, the blue whales called less often. The researchers suggested the animals were spending their energy hunting for food that climate change was making scarcer.

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• 7. Orcas And Parasites

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  Rake-like scars show that blue whales do not always escape the jaws of orcas. Among blue whales photographed off southeastern Australia, 3.7 percent carried rake marks. Among photographed pygmy blue whales off Western Australia, the figure was 42.1 percent. No natural predator of blue whales is well documented, and orcas are behind the only documented attacks. Killing a blue whale takes considerable effort and coordination, so orcas often target calves. How often their attacks prove fatal is unknown.

  The first documented attack came in 1977 off southwestern Baja California, Mexico. The injured whale escaped after five hours. Four more blue whales were seen chased by orcas between 1982 and 2003. In September 2003, a group of orcas in the Eastern Tropical Pacific was found feeding on a recently killed blue whale calf. A whale-watch boat operator recorded orcas harassing a blue whale in Monterey Bay in March 2014. The blue whale defended itself by slapping its tail. A drone filmed a similar incident in the same bay in May 2017. Off the south coast of Western Australia, two attacks were observed directly in 2019 and one more in 2021. The first victim was an adult estimated at 18-22 meters.

  In Antarctic waters, blue whales gather diatoms of the species Cocconeis ceticola and the genus Navicola. These are normally lost when the whales move into warmer water. The barnacles Coronula diadema, Coronula reginae and Cryptolepas rhachianecti grip the skin deeply enough to leave a pit if removed. Whale lice live in skin cracks and are relatively harmless. The copepod Pennella balaenopterae digs in and feeds on the blubber. Inside, the intestinal parasites include the trematodes Ogmogaster and Lecithodesmus, several tapeworm genera, and the thorny-headed worm Bolbosoma. North Atlantic blue whales also carry the protozoans Entamoeba, Giardia and Balantidium.

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• 8. Hunted Nearly Gone

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  In 2017, DNA evidence was used to identify whale bones at Icelandic archaeological sites. Of 124 bones analyzed, more than half came from blue whales, and some dated back to 900 CE. Together with other evidence, this suggests Icelanders were hunting whales in the 9th century, as settlement of Iceland began. They would have been among the earliest known people to hunt the blue whale.

  Size and speed kept blue whales safe from hunters until the mid-19th century, when harpoons that could be shot as projectiles arrived. The catch peaked between 1930 and 1931, when 30,000 animals were taken. In the first half of the 20th century, 350,000-360,000 were killed in the Antarctic, 11,000 in the North Atlantic, mostly around Iceland, and 9,500 in the North Pacific. Blue whales had been abundant in nearly all the world's oceans until the end of the 19th century. By 2015 the global population was estimated at 5,000-15,000 mature individuals, or 10,000-25,000 in total, against at least 140,000 mature whales in 1926.

  Protection arrived in steps. Parts of the Southern Hemisphere were protected from 1939. In 1955 the North Atlantic gained complete protection under the International Convention for the Regulation of Whaling, though Iceland did not recognize it until 1960. The protection reached the Antarctic in 1965 and the North Pacific in 1966. That year the International Whaling Commission banned all blue whale hunting and gave the species worldwide protection. The Soviet Union nonetheless kept hunting blue whales illegally until the 1970s.

  The International Union for Conservation of Nature has listed blue whales as endangered as of 2018. They are also endangered under the U.S. Endangered Species Act. They appear in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, and of the Convention on the Conservation of Migratory Species of Wild Animals. Pygmy blue whales lack enough data on abundance trends, while Antarctic blue whales are critically endangered.

  Ships now cause much of the harm. A total of 17 blue whales were killed or suspected to have been killed by ships off the U.S. West Coast between 1998 and 2019. Five deaths off California in 2007 counted as an unusual mortality event under the Marine Mammal Protection Act. Off Sri Lanka, where whale habitat crosses one of the world's busiest shipping routes, strikes killed eleven blue whales in 2010 and 2012 and at least two in 2014. Two more died off southern Chile in the 2010s. Proposed fixes include better models of where whales gather, shifted shipping lanes, slower vessels, and seasonal and dynamic management of lanes. Entanglement in fishing gear is rarer. The first U.S. report came off California in 2015, apparently from a deep-water trap or pot fishery, and three more followed in 2016. In Sri Lanka, one whale was found with a net through its mouth, along its body and around its tail.

  Noise is a growing burden. Blue whales may hear commercial shipping and seismic surveys for oil and gas exploration. In the Southern California Bight, they called less when mid-frequency active sonar was present. Simulated sonar interrupted deep feeding dives, but animals feeding at shallower depths showed no change. The response also depended on the whale's behavioral state, its horizontal distance from the sound and the availability of prey.

  The effects of pollutants are unknown, and feeding low on the food chain lowers the risk of buildup. Even so, earwax from a male killed by a ship off California held pesticides, flame retardants and mercury. Pollutant profiles suggested a large transfer from mother to young during gestation or nursing. In the Gulf of St. Lawrence, males carry higher concentrations of PCBs and DDT than females, because mothers pass these contaminants on to their young.

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