Blue whale

Whole genome sequencing suggests that blue whales are most closely related to sei whales with gray whales as a sister group. This study also found significant gene flow between minke whales and the ancestors of the blue and sei whale. Blue whales also displayed high genetic diversity.^[13]

Blue whales are known to

Two live blue-fin whale hybrids have since been documented in the Gulf of St. Lawrence (Canada), and in the Azores (Portugal).^[19] DNA tests done in Iceland on a blue whale killed in July 2018 by the Icelandic whaling company Hvalur hf, found that the whale was the offspring of a male fin whale and female blue whale;^[20] however, the results are pending independent testing and verification of the samples. Because the International Whaling Commission classified blue whales as a "Protection Stock", trading their meat is illegal, and the kill is an infraction that must be reported.^[21] Blue-fin hybrids have been detected from genetic analysis of whale meat samples taken from Japanese markets.^[22] Blue-fin whale hybrids are capable of being fertile. Molecular tests on a 21 m (70 ft) pregnant female whale caught off Iceland in 1986 found that it had a blue whale mother and a fin whale father, while its fetus was sired by a blue whale.^[23]

In 2024, a genome analysis of North Atlantic blue whales found evidence that approximately 3.5% of the blue whales' genome was derived from hybridization with fin whales. Gene flow was found to be unidirectional from fin whales to blue whales. Comparison with Antarctic blue whales showed that this hybridization began after the separation of the northern and southern populations. Despite their smaller size, fin whales have similar cruising and sprinting speeds to blue whales, which would allow fin males to complete courtship chases with blue females.^[24]

There is a reference to a humpback–blue whale hybrid in the

• Northern subspecies (B. m. musculus)
  • North Atlantic population – This population is mainly documented from New England along eastern Canada to Greenland, particularly in the Gulf of St. Lawrence, during summer though some individuals may remain there all year. They also aggregate near Iceland and have increased their presence in the Norwegian Sea. They are reported to migrate south to the West Indies, the Azores and northwest Africa.^[27]
  • Eastern North Pacific population – Whales in this region mostly feed off California's coast from summer to fall and then Oregon, Washington State, the Alaska Gyre and Aleutian Islands later in the fall. During winter and spring, blue whales migrate south to the waters of Mexico, mostly the Gulf of California, and the Costa Rica Dome, where they both feed and breed.^[27]
  • Central/Western Pacific population – This stock is documented around the Kamchatka Peninsula during the summer; some individuals may remain there year-round. They have been recorded wintering in Hawaiian waters, though some can be found in the Gulf of Alaska during fall and early winter.^[27]
• Northern Indian Ocean subspecies (B. m. indica) – This subspecies can be found year-round in the northwestern Indian Ocean, though some individuals have recorded travelling to the Crozet Islands during between summer and fall.^[27]
• Pygmy blue whale (B. m. brevicauda)
  • Madagascar population – This population migrates between the
    Crozet Islands and Prince Edward Islands in the south were they feed, passing through the Mozambique Channel.^[27]
  • Australia/Indonesia population – Whales in this region appear to winter off Indonesia and migrate to their summer feeding grounds off the coast of Western Australia, with major concentrations at Perth Canyon and an area stretching from the Great Australian Bight and Bass Strait.^[27]
  • Eastern Australia/New Zealand population – This stock may reside in the Tasman Sea and the Lau Basin in winter and feed mostly in the South Taranaki Bight and off the coast of eastern North Island. Blue whales have been detected around New Zealand throughout the year.^[27]
• Antarctic subspecies (B. m. intermedia) – This subspecies includes all populations found around the Antarctic. They have been recorded to travel as far north as eastern tropical Pacific, the central Indian Ocean, and the waters of southwestern Australia and northern New Zealand.^[27]

Blue whales off the

A 2024 genomic study of the global blue whale population found support for the subspecific status of Antarctic and Indo-western Pacific blue whales but not eastern Pacific blue whales. The study found "...divergence between the eastern North and eastern South Pacific, and among the eastern Indian Ocean, the western South Pacific and the northern Indian Ocean." and "no divergence within the Antarctic".[34]

The blue whale is a slender-bodied cetacean with a broad U-shaped head; thin, elongated

The blue whale is the largest animal known ever to have existed.

The International Whaling Commission (IWC) whaling database reports 88 individuals longer than 30 meters (98 ft), including one of 33 meters (108 ft).^[47] The Discovery Committee reported lengths up to 31 meters (102 ft).^[48] The longest scientifically measured individual blue whale was 30 meters (98 ft) from rostrum tip to tail notch.^[49] Female blue whales are larger than males.^[35][50] Hydrodynamic models suggest a blue whale could not exceed 33 metres (108 ft) because of metabolic and energy constraints.^[51]

The average length of sexually mature female blue whales is 22.0 meters (72.1 ft) for Eastern North Pacific blue whales, 24 meters (79 ft) for central and western North

In 2024, Motani and Pyenson calculated the body mass of blue whales at different lengths, compiling records of their sizes from previous academic literatures and using regression analyses and volumetric analyses. A 25 metres (82 ft) long individual was estimated to weigh approximately 101–119 tonnes (111–131 short tons), while a 30 metres (98 ft) long individual was estimated to weigh approximately 184–205 tonnes (203–226 short tons). Considering that the largest blue whale was indeed 33 metres (108 ft) long, they estimated that a blue whale of such length would have weighed approximately 252–273 tonnes (278–301 short tons).[4]

During the harvest of a female blue whale, Messrs. Irvin and Johnson collected a fetus that is now 70% preserved and used for educational purposes. The fetus was collected in 1922, so some shrinkage may have occurred, making visualization of some features fairly difficult. However, due to this collection researchers now know that the external anatomy of a blue whale fetus is approximately 133 mm. Along with during the developmental phases, the fetus is located where the embryonic and fetal phases converge. This fetus is the youngest gestational age of the specimen recorded.^[58]

Blue whales live around 80–90 years or more.

The blue whale is usually solitary, but can be found in pairs. When productivity is high enough, blue whales can be seen in gatherings of more than 50 individuals.^[35] Populations may go on long migrations, traveling to their summer feeding grounds towards the poles and then heading to their winter breeding grounds in more equatorial waters.^[66] The animals appear to use memory to locate the best feeding areas.^[67] There is evidence of alternative strategies, such as year-round residency, and partial (where only some individuals migrate) or age/sex-based migration. Some whales have been recorded feeding in breeding grounds.^[68] Blue whale typically swim at 2–8 kilometers per hour (1.2–5.0 mph) but may swim faster at 32–36 kilometers per hour (20–22 mph) during encounters with boats, predators or other individuals.^[69] Their massive size limits their ability to breach.^[70]

The greatest dive depth reported from tagged blue whales was 315 meters (1,033 ft).^[71] Their theoretical aerobic dive limit was estimated at 31.2 minutes,^[72] however, the longest dive measured was 15.2 minutes.^[71] The deepest confirmed dive from a pygmy blue whale was 506 meters (1,660 ft).^[73] A blue whale's heart rate can drop to 2 beats per minute (bpm) at deep depths, but upon surfacing, can rise to 37 bpm, which is close to its peak heart rate.^[74]

The blue whale's diet consists almost exclusively of krill.^[35] Blue whales capture krill through lunge feeding; they swim towards them at high speeds as they open their mouths up to 80°.^[35][71] They may engulf 220 metric tons (220 long tons; 240 short tons) of water at one time.^[75] They squeeze the water out through their baleen plates with pressure from the throat pouch and tongue, and swallow the remaining krill.^[35][71] Blue whales have been recorded making 180° rolls during lunge-feeding, possibly allowing them to search the prey field and find the densest patches.^[76]

While pursuing krill patches, blue whales maximize their calorie intake by increasing the number of lunges while selecting the thickest patches. This provides them enough energy for everyday activities while storing additional energy necessary for migration and reproduction. Due to their size, blue whales have larger energetic demands than most animals resulting in their need for this specific feeding habit.^[77] Blue whales have to engulf densities greater than 100 krill/m³ to maintain the cost of lunge feeding.^[71][78] They can consume 34,776–1,912,680 kilojoules (8,312–457,141 kcal) from one mouthful of krill, which can provide up to 240 times more energy than used in a single lunge.^[71] It is estimated that an average-sized blue whale must consume 1,120 ± 359 kilograms (2,469 ± 791 lb) of krill a day.^[79][80] On average, an blue whale eats 4 t (3.9 long tons; 4.4 short tons) each day.^[59]

In the southern ocean, blue whales feed on Antarctic krill (Euphausia superba). In the South Australia, pygmy blue whales (B. m. brevicauda) feeds on Nyctiphanes australis.^[81] In California, they feed mostly on Thysanoessa spinifera, but also less commonly on North pacific krill (Euphausia pacifica).^[82] Research of the Eastern North Pacific population shows that when diving to feed on krill, the whales reach an average depth of 201 meters, with dives lasting 9.8 minutes on average.^[81]

While most blue whales feed almost exclusively on krill, the Northern Indian Ocean subspecies (B. m. indica) instead feeds predominantly on sergestid shrimp. To do so, they dive deeper and for longer periods of time than blue whales in other regions of the world, with dives of 10.7 minutes on average, and a hypothesized dive depth of about 300 meters. Fecal analysis also found the presence of fish, krill, amphipods, cephalopods, and scyphozoan jellyfish in their diet.^[81]

Blue whales appear to avoid directly competing with other baleen whales.^[83][84][85] Different whale species select different feeding spaces and times as well as different prey species.^[75][86][87] In the Southern Ocean, baleen whales appear to feed on Antarctic krill of different sizes, which may lessen competition between them.^[88]

Blue whale feeding habits may differ due to situational disturbances, like environmental shifts or human interference. This can cause a change in diet due to stress response. Due to these changing situations, there was a study performed on blue whales measuring cortisol levels and comparing them with the levels of stressed individuals, it gave a closer look to the reasoning behind their diet and behavioral changes.^[89]

The age of sexual maturity for blue whales is thought to be 5–15 years.^[90] In the Northern Hemisphere, the length at which they reach maturity is 21–23 meters (69–75 ft) for females and 20–21 meters (66–69 ft) for males. In the Southern Hemisphere, the length of maturity is 23–24 meters (75–79 ft) and 22 meters (72 ft) for females and males respectively.^[91] Male pygmy blue whales average 18.7 meters (61.4 ft) at sexual maturity.^[92][93] Female pygmy blue whales are 21.0–21.7 meters (68.9–71.2 ft) in length^[52] and roughly 10 years old at the age of sexual maturity.^[52][53][94] Since corpora are added every ~2.5 years after sexual maturity, physical maturity is assumed to occur at 35 years.^[95] Little is known about mating behavior, or breeding and birthing areas.^[45][91] Blue whales appear to be polygynous, with males competing for females.^[91][96] A male blue whale typically trails a female and will fight off potential rivals.^[97] The species mates from fall to winter.^[45][91]

Pregnant females eat roughly four percent of their body weight daily,

A blue whale song

Recorded in the Atlantic (1)

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A blue whale song

Recorded in the Atlantic (2)

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A blue whale song

Recorded in North Eastern Pacific

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A blue whale song

Recorded in the South Pacific

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A blue whale song

Recorded in the West Pacific

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Blue whales produce some of the loudest and lowest frequency vocalizations in the animal kingdom,^[27] and their inner ears appear well adapted for detecting low-frequency sounds.^[103] The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz.^[104] Blue whale songs vary between populations.^[105]

Vocalizations produced by the Eastern North Pacific population have been well studied. This population produces pulsed calls ("A") and tonal calls ("B"), upswept tones that precede type B calls ("C") and separate downswept tones ("D").^[106][107] A and B calls are often produced in repeated co-occurring sequences and sung only by males, suggesting a reproductive function.^[107][108] D calls may have multiple functions. They are produced by both sexes during social interactions while feeding.^[108][109] and by males when competing for mates.^[97]

Blue whale calls recorded off Sri Lanka have a three-unit phrase. The first unit is a 19.8 to 43.5 Hz pulsive call, and is normally 17.9 ± 5.2 seconds long. The second unit is a 55.9 to 72.4 Hz FM upsweep that is 13.8 ± 1.1 seconds long. The final unit is 28.5 ± 1.6 seconds long with a tone of 108 to 104.7 Hz.^[110] A blue whale call recorded off Madagascar, a two-unit phrase,^[111] consists of 5–7 pulses with a center frequency of 35.1 ± 0.7 Hz lasting 4.4 ± 0.5 seconds proceeding a 35 ± 0 Hz tone that is 10.9 ± 1.1 seconds long.^[110] In the Southern Ocean, blue whales produce 18-second vocals which start with a 9-second-long, 27 Hz tone, and then a 1-second downsweep to 19 Hz, followed by a downsweep further to 18 Hz.^[112][113] Other vocalizations include 1–4 second long, frequency-modulated calls with a frequency of 80 and 38 Hz.^[113][114]

There is evidence that some blue whale songs have temporally declined in tonal frequency.^{[115][116][117]} The vocalization of blue whales in the Eastern North Pacific decreased in tonal frequency by 31% from the early 1960s to the early 21st century.^[115][116] The frequency of pygmy blue whales in the Antarctic has decreased by a few tenths of a hertz every year starting in 2002.^[117] It is possible that as blue whale populations recover from whaling, there is increasing sexual selection pressure (i.e., a lower frequency indicates a larger body size).^[116]

The only known natural predator to blue whales is the

Conservation

The global blue whale population is estimated to be 5,000–15,000 mature individuals and 10,000–25,000 total as of 2018. By comparison, there were at least 140,000 mature whales in 1926. There are an estimated total of 1,000–3,000 whales in the North Atlantic, 3,000–5,000 in the North Pacific, and 5,000–8,000 in the Antarctic. There are possibly 1,000–3,000 whales in the eastern South Pacific while the pygmy blue whale may number 2,000–5,000 individuals.

Endangered Species Act.^[66]

Blue whales are formally classified as

Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)^[132] and the Convention on the Conservation of Migratory Species of Wild Animals.^[133] Although, for some populations, there is not enough information on current abundance trends (e.g., pygmy blue whales), others are critically endangered (e.g., Antarctic blue whales).^[134][135]

Threats

In 2017, DNA evidence was used to identify whale bones at Icelandic archaeological sites. Of the 124 bones analyzed more than 50% were from blue whales and some dated as far back as 900 CE. This, and other evidence, suggests that Icelanders were hunting whales as early as the 9th century, just as the settlement of Iceland began. Thus Icelanders would have been among the earliest known humans to hunt the blue whale.^[136]

Blue whales were initially difficult to hunt because of their size and speed.^[27] This began to change in the mid-19th century with the development of harpoons that can be shot as projectiles.^[137] Blue whale whaling peaked between 1930 and 1931 with 30,000 animals taken. Harvesting of the species was particularly high in the Antarctic, with 350,000–360,000 whales taken in the first half of the 20th century. In addition, 11,000 North Atlantic whales (mostly around Iceland) and 9,500 North Pacific whales were killed during the same period.^[91] The International Whaling Commission banned all hunting of blue whales in 1966 and gave them worldwide protection.^[138] However, the Soviet Union continued to illegally hunt blue whales and other species up until the 1970s.^[139]

U.S. West Coast.^[140] A total of 17 blue whales were killed or suspected to have been killed by ships between 1998 and 2019 off the U.S. West Coast.^[27] Five deaths in 2007 off California were considered an unusual mortality event, as defined under the Marine Mammal Protection Act.^[140][141] Lethal ship strikes are also a problem in Sri Lankan waters, where their habitat intersects with one of the world's most active shipping routes.^[142] Here, strikes caused the deaths of eleven blue whales in 2010 and 2012,^[143] and at least two in 2014.^[144] Ship-strike mortality claimed the lives of two blue whales off southern Chile in the 2010s.^[145][146] Possible measures for reducing future ship strikes include better predictive models of whale distribution, changes in shipping lanes, vessel speed reductions, and seasonal and dynamic management of shipping lanes.^[147][148] Few cases of blue whale entanglement in commercial fishing gear have been documented. The first report in the U.S. occurred off California in 2015, reportedly some type of deep-water trap/pot fishery.^[149] Three more entanglement cases were reported in 2016.^[150] In Sri Lanka, a blue whale was documented with a net wrapped through its mouth, along the sides of its body, and wound around its tail.^[151]

Increasing

man-made underwater noise impacts blue whales.^[152][153] They may be exposed to noise from commercial shipping^[154][155] and seismic surveys as a part of oil and gas exploration.^[156][157] Blue whales in the Southern California Bight decreased calling in the presence of mid-frequency active (MFA) sonar.^[158] Exposure to simulated MFA sonar was found to interrupt blue whale deep-dive feeding, but no changes in behavior were observed in individuals feeding at shallower depths. The responses also depended on the animal's behavioral state, its (horizontal) distance from the sound source and the availability of prey.^[159]

The potential impacts of

metabolites, and several other organochlorine compounds relative to females, reflecting maternal transfer of these persistent contaminants from females into young.^[162]

See also

• Largest organisms
• List of cetaceans
• List of largest mammals
• List of whale vocalizations

Note

1. ^ The extinct whale species Perucetus colossus (described in 2023) has been suggested as a potential contender of the blue whale in size,^[3] however, this was later disputed in 2024.^[4] Several extinct dinosaurs may also have reached a similar mass to the blue whale.^[5]

References