Blue whale

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The blue whale (Balaenoptera musculus) is a marine mammal and a baleen whale. Reaching a maximum confirmed length of Template:Cvt and weighing up to Template:Cvt, it is the largest animal known ever to have existed.Template:Efn The blue whale's long and slender body can be of various shades of greyish-blue on its upper surface and somewhat lighter underneath. Four subspecies are recognized: B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, B. m. brevicauda (the pygmy blue whale) in the Indian Ocean and South Pacific Ocean, and B. m. indica in the Northern Indian Ocean. There is a population in the waters off Chile that may constitute a fifth subspecies.

In general, blue whale populations migrate between their summer feeding areas near the poles and their winter breeding grounds near the tropics. There is also evidence of year-round residencies, and partial or age/sex-based migration. Blue whales are filter feeders; their diet consists almost exclusively of krill. They are generally solitary or gather in small groups, and have no well-defined social structure other than mother–calf bonds. Blue whales vocalize, with a fundamental frequency ranging from 8 to 25 Hz; their vocalizations may vary by region, season, behavior, and time of day. Orcas are their only natural predators.

The blue whale was abundant in nearly all the Earth's oceans until the end of the 19th century. It was hunted almost to the point of extinction by whalers until the International Whaling Commission banned all blue whale hunting in 1966. The International Union for Conservation of Nature has listed blue whales as Endangered as of 2018. It continues to face numerous man-made threats such as ship strikes, pollution, ocean noise, and climate change. Scientists found evidence of this through morphological or epidemiological analysis. These analyses are accompanied by chemical profiles that use fecal and tissue which continue to prove the impact of man-made threats.

Taxonomy

Nomenclature

The genus name, Balaenoptera, means winged whale,<ref name=Reeves_etal_2002/> while the species name, musculus, could mean "muscle" or a diminutive form of "mouse", possibly a pun by Carl Linnaeus<ref name=Reeves_etal_2002/><ref name=Calamb_Steig_1997/> when he named the species in Systema Naturae.<ref name=Linnaeus_1758>Template:Cite book</ref> One of the first published descriptions of a blue whale comes from Robert Sibbald's Phalainologia Nova,<ref name=Sibbald_1692>Template:Cite journal</ref> after Sibbald found a stranded whale in the estuary of the Firth of Forth, Scotland, in 1692. The name "blue whale" was derived from the Norwegian blåhval, coined by Svend Foyn shortly after he had perfected the harpoon gun. The Norwegian scientist G. O. Sars adopted it as the common name in 1874.<ref name=Bortolotti_2008>Template:Cite book</ref>

Blue whales were referred to as "Sibbald's rorqual", after Robert Sibbald, who first described the species.<ref name=Sibbald_1692/> Whalers sometimes referred to them as "sulphur bottom" whales, as the bellies of some individuals are tinged with yellow.<ref name=":0">Template:Cite journal</ref> This tinge is due to a coating of huge numbers of diatoms.<ref name=":0" /> (Herman Melville briefly refers to "sulphur bottom" whales in his novel Moby-Dick.<ref name="Melville_1851" />)

Evolution

Template:Cladogram Blue whales are rorquals in the family Balaenopteridae. A 2018 analysis estimates that the Balaenopteridae family diverged from other families in between 10.48 and 4.98 million years ago during the late Miocene.<ref name=Arnason_etal_2018>Template:Cite journal</ref> The earliest discovered anatomically modern blue whale is a partial skull fossil from southern Italy identified as B. cf. musculus, dating to the Early Pleistocene, roughly 1.5–1.25 million years ago.<ref name=Bianucci_etal_2019>Template:Cite journal</ref> The Australian pygmy blue whale diverged during the Last Glacial Maximum. Their more recent divergence has resulted in the subspecies having a relatively low genetic diversity,<ref name=Attard_etal_2015>Template:Cite journal</ref> and New Zealand blue whales have an even lower genetic diversity.<ref name=Barlow_etal_2018>Template:Cite journal</ref>

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.<ref name=Arnason_etal_2018/>

Hybridization

Blue whales are known to interbreed with fin whales.<ref>This may have already been known to Icelanders in the 17th century, see Template:Cite book</ref> The earliest description of a possible hybrid between a blue whale and a fin whale was a Template:Cvt anomalous female whale with the features of both the blue and the fin whales taken in the North Pacific.<ref name=Doroshenko_1970>Template:Cite journal</ref> A whale captured off northwestern Spain in 1984, was found to have been the product of a blue whale mother and a fin whale father.<ref name=Berube_Aguilar_1998>Template:Cite journal</ref>

Two live blue-fin whale hybrids have since been documented in the Gulf of St. Lawrence (Canada), and in the Azores (Portugal).<ref name=Berube_etal_2017>Template:Cite conference</ref> 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;<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Blue-fin hybrids have been detected from genetic analysis of whale meat samples taken from Japanese markets.<ref name=Palumbi_Cipriano_1998>Template:Cite journal</ref> Blue-fin whale hybrids are capable of being fertile. Molecular tests on a Template:Cvt 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.<ref name=Spilliaert_etal_1991>Template:Cite journal</ref>

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.<ref name=Jossey_et_al_2024>Template:Cite journal</ref>

There is a reference to a humpback–blue whale hybrid in the South Pacific, attributed to marine biologist Michael Poole.<ref name=Reeves_etal_2002/><ref name=Hatch_etal_2006>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Subspecies and stocks

At least four subspecies of blue whale are traditionally recognized, some of which are divided into population stocks or "management units".<ref name=NOAA>Template:Cite report</ref><ref name=SMM_2016>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They have a worldwide distribution, but are mostly absent from the Arctic Ocean and the Mediterranean, Okhotsk, and Bering Sea.<ref name=NOAA/>

File:Blue Whale 001 body bw.jpg

Aerial view of adult blue whale

• 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.<ref name=NOAA/>
  • 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.<ref name=NOAA/>
  • 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.<ref name=NOAA/>
• 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.<ref name=NOAA/>
• Pygmy blue whale (B. m. brevicauda)
  • Madagascar population – This population migrates between the Seychelles and Amirante Islands in the north and the Crozet Islands and Prince Edward Islands in the south were they feed, passing through the Mozambique Channel.<ref name=NOAA/>
  • 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.<ref name=NOAA/>
  • 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.<ref name=NOAA/>
• 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.<ref name=NOAA/>

Blue whales off the Chilean coast might be a separate subspecies based on their geographic separation, genetics, and unique song types.<ref name=LeDuc_etal_2007>Template:Cite journal</ref><ref name=Torres-Florez_etal_2015>Template:Cite journal</ref><ref name=Buchan_etal_2010>Template:Cite journal</ref> Chilean blue whales might overlap in the Eastern Tropical Pacific with Antarctica blue whales and Eastern North Pacific blue whales. Chilean blue whales are genetically differentiated from Antarctica blue whales such that interbreeding is unlikely. However, the genetic distinction is less between them and the Eastern North Pacific blue whale, hence there might be gene flow between the Southern and Northern Hemispheres.<ref name=LeDuc_etal_2016>Template:Cite journal</ref> A 2019 study by Luis Pastene, Jorge Acevedo and Trevor Branch provided new morphometric data from a survey of 60 Chilean blue whales, hoping to address the debate about the possible distinction of this population from others in the Southern Hemisphere. Data from this study, based on whales collected in the 1965/1966 whaling season, shows that both the maximum and mean body length of Chilean blue whales lies between these values in pygmy and Antarctic blue whales. Data also indicates a potential difference in snout-eye measurements between the three, and a significant difference in fluke-anus length between the Chilean population and pygmy blue whales. This further confirms Chilean blue whales as a separate population, and implies that they do not fall under the same subspecies as the pygmy blue whale (B. m. brevicauda).<ref name=Pastene_etal_2019>Template:Cite journal</ref>

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".<ref>Template:Cite journal</ref>

Description

File:Bluewhale2 noaa.jpg

A blue whale with its bow wave, showing the blowhole

The blue whale is a slender-bodied cetacean with a broad U-shaped head; thin, elongated flippers; a small Template:Convert sickle-shaped dorsal fin located close to the tail, and a large tail stock at the root of the wide and thin flukes. The upper jaw is lined with 70–395 black baleen plates. The throat region has 60–88 grooves which allows the skin to expand during feeding.<ref name="Reeves_etal_2002">Template:Cite book</ref><ref name="Calamb_Steig_1997" /><ref name="Sears_Perr_2009" /><ref name="Leatherwood_etal_1976" /><ref name="Leatherwood_etal_1982">Template:Cite journal</ref> It has two blowholes that can squirt Template:Convert up in the air.<ref name="Reeves_etal_2002" /><ref name="Sears_Perr_2009" /><ref name="Leatherwood_etal_1976" /> The skin has a mottled grayish-blue coloration, appearing blue underwater.<ref name=Calamb_Steig_1997>Template:Cite book</ref><ref name=Sears_Perr_2009>Template:Cite book</ref><ref name="Leatherwood_etal_1976">Template:Cite journal</ref> The mottling patterns near the dorsal fin vary between individuals.<ref name="Sears_etal_1990">Template:Cite journal</ref><ref name="Calambokidis_etal_2009">Template:Cite journal</ref><ref name="Gendron_2012">Template:Cite journal</ref> The underbelly has lighter pigmentation and can appear yellowish due to diatoms in the water,<ref name="Calamb_Steig_1997" /><ref name="Sears_Perr_2009" /><ref name="Leatherwood_etal_1976" /> which historically earned them the nickname "sulphur bottom".<ref name="Melville_1851">Template:Cite book</ref><ref name="Scammon_1874">Template:Cite book</ref> The male blue whale has the largest penis in the animal kingdom, at around Template:Convert long and Template:Convert wide.<ref name = "bioweb">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Size

File:Joey williams with a 19 foot long blue whale skull.jpg

A blue whale skull measuring Template:Convert

The blue whale is the largest animal known ever to have existed.<ref name="Ruud_1956">Template:Cite journal</ref><ref name="Lockyer_1981">Template:Cite journal</ref><ref name="Mizroch_1984">Template:Cite journal</ref> Some studies have estimated that certain shastasaurid ichthyosaurs and the ancient whale Perucetus could have rivalled the blue whale in size, with Perucetus actually being heavier with a mean weight of Template:Cvt.<ref name="AT23" /><ref name="PLOS One2018">Template:Cite journal</ref> However, these estimates were based on fragmentary remains, and the proposed size for Perucetus was disputed by studies in 2024.<ref name=MP24>Template:Cite journal</ref> Other studies estimate that, on land, large sauropods like Bruhathkayosaurus (mean weight: 110–170 tons) and Maraapunisaurus (mean weight: 80–120 tons) might have rivalled the blue whale, with the former even exceeding the blue whale based on its most liberal estimates (240 tons). However, these estimates were based on even more fragmentary specimens that had disintegrated by the time estimates could be made.<ref name="Bruhathkayosaurus2023">Template:Cite journal</ref>

The International Whaling Commission (IWC) whaling database reports 88 individuals longer than Template:Convert, including one of Template:Convert.<ref name="McClain_2015">Template:Cite journal</ref> The Discovery Committee reported lengths up to Template:Convert.<ref name=Mackintosh_1942>Template:Cite journal</ref> The longest scientifically measured individual blue whale was Template:Convert from rostrum tip to tail notch.<ref name=Sears_Calamb_2002>Template:Cite book</ref> Female blue whales are larger than males.<ref name=Sears_Perr_2009/><ref name=Ralls_1976>Template:Cite journal</ref> Hydrodynamic models suggest a blue whale could not exceed Template:Convert because of metabolic and energy constraints.<ref name=Potvin_2012>Template:Cite journal</ref>

The average length of sexually mature female blue whales is Template:Convert for Eastern North Pacific blue whales, Template:Convert for central and western North Pacific blue whales, Template:Convert for North Atlantic blue whales, Template:Convert for Antarctic blue whales, Template:Convert for Chilean blue whales, and Template:Convert for pygmy blue whales.<ref name="McClain_2015"/><ref name=Branch_2007a>Template:Cite journal</ref><ref name=Gilpatrick_Perryman_2008>Template:Cite journal</ref>

In the Northern Hemisphere, males weigh an average Template:Convert and females Template:Convert. Eastern North Pacific blue whale males average Template:Convert and females Template:Convert. Antarctic males average Template:Convert and females Template:Convert. Pygmy blue whale males average Template:Convert to Template:Convert.<ref name=Lockyer_1976>Template:Cite journal</ref> The weight of the heart of a stranded North Atlantic blue whale was Template:Convert, the largest known in any animal.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The record-holder blue whale was recorded at Template:Convert,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> with estimates of up to Template:Convert.<ref>Template:Cite journal</ref>

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 Template:Convert long individual was estimated to weigh approximately Template:Convert, while a Template:Convert long individual was estimated to weigh approximately Template:Convert. Considering that the largest blue whale was indeed Template:Convert long, they estimated that a blue whale of such length would have weighed approximately Template:Convert.<ref name=MP24/>

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.<ref>Template:Cite journal</ref>

Life span

Blue whales live around 80–90 years or more.<ref name=Sears_Perr_2009/><ref name=natgeo/> Scientists look at a blue whale's earwax or ear plug to estimate its age. Each year, a light and dark layer of wax is laid corresponding with fasting during migration and feeding time. Each set is thus an indicator of age.<ref name=Purves_1955>Template:Cite journal</ref><ref name=Gabriele_etal_2010>Template:Cite journal</ref><ref name=Lockyer_1984a>Template:Cite journal</ref> The oldest blue whale found was determined, using this method, to be 110 years old.<ref name=natgeo>Template:Cite magazine</ref><ref name=wdc>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The maximum age of a pygmy blue whale determined this way is 73 years.<ref name=Branch_2008>Template:Cite journal</ref> In addition, female blue whales develop scars or corpora albicantia on their ovaries every time they ovulate.<ref name=Perr_Donov_1984>Template:Cite book</ref> In a female pygmy blue whale, one corpus albicans is formed on average every 2.6 years.<ref name=Branch_2008/>

Behavior and ecology

File:Bluewhale1 noaa crop.jpg

The blow of a blue whale

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.<ref name=Sears_Perr_2009/> 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.<ref name=NOAAblue>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The animals appear to use memory to locate the best feeding areas.<ref>Template:Cite journal</ref> 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.<ref name=Geijer_etal_2016>Template:Cite journal</ref> Blue whale typically swim at Template:Convert but may swim faster at Template:Convert during encounters with boats, predators or other individuals.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Their massive size limits their ability to breach.<ref>Template:Cite journal</ref>

The greatest dive depth reported from tagged blue whales was Template:Convert.<ref name=Goldbogen_etal_2011/> Their theoretical aerobic dive limit was estimated at 31.2 minutes,<ref name=Croll_etal_2001>Template:Cite journal</ref> however, the longest dive measured was 15.2 minutes.<ref name=Goldbogen_etal_2011/> The deepest confirmed dive from a pygmy blue whale was Template:Convert.<ref name=Owen_etal_2016>Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref>

Diet and feeding

File:Blue-whale.jpg

Blue near the surface after feeding

The blue whale's diet consists almost exclusively of krill.<ref name=Sears_Perr_2009/> Blue whales capture krill through lunge feeding; they swim towards them at high speeds as they open their mouths up to 80°.<ref name=Sears_Perr_2009/><ref name=Goldbogen_etal_2011/> They may engulf Template:Convert of water at one time.<ref name=Fossette_etal_2017>Template:Cite journal</ref> They squeeze the water out through their baleen plates with pressure from the throat pouch and tongue, and swallow the remaining krill.<ref name=Sears_Perr_2009/><ref name=Goldbogen_etal_2011>Template:Cite journal</ref> Blue whales have been recorded making 180° rolls during lunge-feeding, possibly allowing them to search the prey field and find the densest patches.<ref name=Goldbogen_etal_2012>Template:Cite journal</ref>

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.<ref>Template:Cite journal</ref> Blue whales have to engulf densities greater than 100 krill/m³ to maintain the cost of lunge feeding.<ref name=Goldbogen_etal_2011/><ref name=Hazen_etal_2015>Template:Cite journal</ref> They can consume Template:Convert from one mouthful of krill, which can provide up to 240 times more energy than used in a single lunge.<ref name=Goldbogen_etal_2011/> It is estimated that an average-sized blue whale must consume Template:Convert of krill a day.<ref name=Brodie_1975>Template:Cite journal</ref><ref name=Croll_etal_2006>Template:Cite book</ref> On average, a blue whale eats Template:Cvt each day.<ref name=natgeo/>

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.<ref name=":1">Template:Cite journal</ref> In California, they feed mostly on Thysanoessa spinifera, but also less commonly on North pacific krill (Euphausia pacifica).<ref>Template:Cite journal</ref> 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.<ref name=":1" />

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.<ref name=":1" />

Blue whales appear to avoid directly competing with other baleen whales.<ref name=Hardin_1960>Template:Cite journal</ref><ref name=Hutchinson_1961>Template:Cite journal</ref><ref name=Pianka_1974>Template:Cite journal</ref> Different whale species select different feeding spaces and times as well as different prey species.<ref name=Fossette_etal_2017/><ref name=Doniol-Valcroze_2008>Template:Cite thesis</ref><ref name=Friedlaender_etal_2015>Template:Cite journal</ref> In the Southern Ocean, baleen whales appear to feed on Antarctic krill of different sizes, which may lessen competition between them.<ref name=Santora_etal_2010>Template:Cite journal</ref>

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Reproduction and birth

File:BlueWhaleWithCalf.jpg

A blue whale calf with its mother

The age of sexual maturity for blue whales is thought to be 5–15 years.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In the Northern Hemisphere, the length at which they reach maturity is Template:Convert for females and Template:Convert for males. In the Southern Hemisphere, the length of maturity is Template:Convert and Template:Convert for females and males respectively.<ref name=Sears_Perrin_2018>Template:Cite book</ref> Male pygmy blue whales average Template:Convert at sexual maturity.<ref name=Ichihara_1964>Template:Cite journal</ref><ref name=Sazhinov_1970>Template:Cite journal</ref> Female pygmy blue whales are Template:Convert in length<ref name=Branch_2007a/> and roughly 10 years old at the age of sexual maturity.<ref name=Branch_2007a/><ref name=Gilpatrick_Perryman_2008/><ref name=Branch_Mikhalev_2008>Template:Cite journal</ref> Since corpora are added every ~2.5 years after sexual maturity, physical maturity is assumed to occur at 35 years.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Little is known about mating behavior, or breeding and birthing areas.<ref name=Mizroch_1984/><ref name=Sears_Perrin_2018/> Blue whales appear to be polygynous, with males competing for females.<ref name=Sears_Perrin_2018/><ref name=Sears_etal_2013>Template:Cite journal</ref> A male blue whale typically trails a female and will fight off potential rivals.<ref name=Schall_etal_2019>Template:Cite journal</ref> The species mates from fall to winter.<ref name=Mizroch_1984/><ref name=Sears_Perrin_2018/>

Pregnant females eat roughly four percent of their body weight daily,<ref name=Sergeant_1969>Template:Cite journal</ref> amounting to 60% of their overall body weight throughout summer foraging periods.<ref name=Sears_Perrin_2018/><ref name=Lockyer_1984b>Template:Cite journal</ref> Gestation may last 10–12 months with calves being Template:Convert long and weighing Template:Convert at birth.<ref name=Sears_Perrin_2018/> Estimates suggest that because calves require Template:Convert milk per kg of mass gain, blue whales likely produce Template:Convert of milk per day (ranging from Template:Convert of milk per day).<ref name=Oftedal_1997>Template:Cite journal</ref> The first video of a calf thought to be nursing was filmed in New Zealand in 2016.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Calves may be weaned when they reach 6–8 months old at a length of Template:Convert.<ref name=Sears_Perrin_2018/> They gain roughly Template:Convert during the weaning period.<ref name=Lockyer_1981/> Interbirth periods last two to three years;<ref name=Sears_Perrin_2018/> they average 2.6 years in pygmy blue whales.<ref name=Branch_2008/> Mother-calf pairings are infrequently observed, and this may be due to mothers birthing and weaning their young in-between their entry and return to their summer feeding grounds.<ref>Template:Cite journal</ref>

Vocalizations

{{#invoke:Listen|main}} Blue whales produce some of the loudest and lowest frequency vocalizations in the animal kingdom,<ref name=NOAA/> and their inner ears appear well adapted for detecting low-frequency sounds.<ref name=Yamato_etal_2008>Template:Cite journal</ref> The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz.<ref name=Stafford_etal_1998>Template:Cite journal</ref> Blue whale songs vary between populations.<ref name=McDonald_etal_2006>Template:Cite journal</ref>

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").<ref name=Aroyan_etal_2000>Template:Cite book</ref><ref name=McDonald_etal_2001>Template:Cite journal</ref> A and B calls are often produced in repeated co-occurring sequences and sung only by males, suggesting a reproductive function.<ref name=McDonald_etal_2001/><ref name=Oleson_etal_2007a>Template:Cite journal</ref> D calls may have multiple functions. They are produced by both sexes during social interactions while feeding.<ref name=Oleson_etal_2007a/><ref name=Lewis_etal_2018>Template:Cite journal</ref> and by males when competing for mates.<ref name=Schall_etal_2019/>

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.<ref name=Stafford_etal_2010>Template:Cite journal</ref> A blue whale call recorded off Madagascar, a two-unit phrase,<ref name=Ljungblad_etal_1998>Template:Cite report</ref> 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.<ref name=Stafford_etal_2010/> 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.<ref name=Sirovic_etal_2004>Template:Cite journal</ref><ref name=Rankin_etal_2005/> Other vocalizations include 1–4 second long, frequency-modulated calls with a frequency of 80 and 38 Hz.<ref name=Rankin_etal_2005>Template:Cite journal</ref><ref name=Sirovic_etal_2006>Template:Cite journal</ref>

There is evidence that some blue whale songs have temporally declined in tonal frequency.<ref name=Nieukirk_etal_2005>Template:Cite conference</ref><ref name=McDonald_etal_2009>Template:Cite journal</ref><ref name=Leroy_etal_2018>Template:Cite journal</ref> 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.<ref name=Nieukirk_etal_2005/><ref name=McDonald_etal_2009/> The frequency of pygmy blue whales in the Antarctic has decreased by a few tenths of a hertz every year starting in 2002.<ref name=Leroy_etal_2018/> 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).<ref name=McDonald_etal_2009/>

Predators

The only known natural predator to blue whales is the orca, although the rate of fatal attacks by orcas is unknown. Photograph-identification studies of blue whales have estimated that a high proportion of the individuals in the Gulf of California have rake-like scars, indicative of encounters with orcas.<ref name=Sears_1990>Template:Cite journal</ref> Off southeastern Australia, 3.7% of blue whales photographed had rake marks and 42.1% of photographed pygmy blue whales off Western Australia had rake marks.<ref name=Mehta_etal_2007>Template:Cite journal</ref> Documented predation by orcas has been rare. A blue whale mother and calf were first observed being chased at high speeds by orcas off southeastern Australia.<ref name=Cotton_1944>Template:Cite journal</ref> The first documented attack occurred in 1977 off southwestern Baja California, Mexico, but the injured whale escaped after five hours.<ref name=Tarpy_1979>Template:Cite journal</ref> Four more blue whales were documented as being chased by a group of orcas between 1982 and 2003.<ref name=Ford_Reeves_2008>Template:Cite journal</ref> The first documented predation event by orcas occurred in September 2003, when a group of orcas in the Eastern Tropical Pacific was encountered feeding on a recently killed blue whale calf.<ref name=Pitman_etal_2007>Template:Cite journal</ref> In March 2014, a commercial whale watch boat operator recorded an incident involving a group of orcas harassing a blue whale in Monterey Bay. The blue whale defended itself by slapping its tail.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A similar incident was recorded by a drone in Monterey Bay in May 2017.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The first direct observations of orca predation occurred off the south coast of Western Australia, two in 2019 and one more in 2021. The first victim was estimated to be Template:Convert.<ref>Template:Cite journal</ref>

Infestations and health threats

In Antarctic waters, blue whales accumulate diatoms of the species Cocconeis ceticola and the genera Navicola, which are normally removed when the whales enter warmer waters. Barnacles such as Coronula diadema, Coronula reginae, and Cryptolepas rhachianecti, latch on to whale skin deep enough to leave behind a pit if removed. Whale lice species make their home in cracks of the skin and are relatively harmless. The copepod species Pennella balaenopterae digs in and attaches itself to the blubber to feed on. Intestinal parasites include the trematode genera Ogmogaster and Lecithodesmus; the tapeworm genera Priapocephalus, Phyllobotrium, Tetrabothrius, Diphyllobotrium, and Diplogonoporus; and the thorny-headed worm genus Bolbosoma. In the North Atlantic, blue whales also contain the protozoans Entamoeba, Giardia and Balantidium.<ref>Template:Cite journal</ref>

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.<ref name="iucn"/> Blue whales have been protected in areas of the Southern Hemisphere since 1939. In 1955, they were given complete protection in the North Atlantic under the International Convention for the Regulation of Whaling; this protection was extended to the Antarctic in 1965 and the North Pacific in 1966.<ref name=Gambell_1979>Template:Cite journal</ref><ref name=Best_1993>Template:Cite journal</ref> The protected status of North Atlantic blue whales was not recognized by Iceland until 1960.<ref name="Sigurjónsson_1988">Template:Cite journal</ref> In the United States, the species is protected under the Endangered Species Act.<ref name=NOAAblue/>

Blue whales are formally classified as endangered under both the U.S. Endangered Species Act<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and the IUCN Red List.<ref name="iucn"/> They are also listed on Appendix I under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and the Convention on the Conservation of Migratory Species of Wild Animals.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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).<ref name=Samaran_etal_2013>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Threats

File:FMIB 34640 Large Hump-Back -sic- Whale, 83 Feet Long.jpeg

Dead blue whale on flensing platform

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.<ref>Template:Cite news</ref>

Blue whales were initially difficult to hunt because of their size and speed.<ref name=NOAA/> This began to change in the mid-19th century with the development of harpoons that can be shot as projectiles.<ref>Template:Cite book</ref> 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.<ref name=Sears_Perrin_2018/> The International Whaling Commission banned all hunting of blue whales in 1966 and gave them worldwide protection.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, the Soviet Union continued to illegally hunt blue whales and other species up until the 1970s.<ref>Template:Cite journal</ref>

File:Blue whale ship strike death.jpg

Researchers examine a dead blue whale killed by collision with a ship

Ship strikes are a significant mortality factor for blue whales, especially off the U.S. West Coast.<ref name="Berman-Kowalewski_etal_2010">Template:Cite journal</ref> 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.<ref name="NOAA" /> Five deaths in 2007 off California were considered an unusual mortality event, as defined under the Marine Mammal Protection Act.<ref name=Berman-Kowalewski_etal_2010/><ref name=Abramson_etal_2009>Template:Cite report</ref> 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.<ref name=deVos_etal_2016>Template:Cite journal</ref> Here, strikes caused the deaths of eleven blue whales in 2010 and 2012,<ref name=Priyadarshana_etal_2015>Template:Cite report</ref> and at least two in 2014.<ref name=Randage_etal_2014>Template:Cite journal</ref> Ship-strike mortality claimed the lives of two blue whales off southern Chile in the 2010s.<ref name=Brownell_etal_2014>Template:Cite report</ref><ref name=IWC_2017>Template:Cite report</ref> 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.<ref name=Redfern_etal_2013>Template:Cite journal</ref><ref name=Dransfield_etal_2014>Template:Cite journal</ref> 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.<ref name=Carretta_etal_2017>Template:Cite report</ref> Three more entanglement cases were reported in 2016.<ref name=NMFS_2017>Template:Cite report</ref> 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.<ref name=deVos_2015>Template:Cite book</ref>

Increasing man-made underwater noise impacts blue whales.<ref name=Southall_etal_2018>Template:Cite journal</ref><ref name=Wiggins_etal_2001>Template:Cite journal</ref> They may be exposed to noise from commercial shipping<ref name=McKenna_etal_2012>Template:Cite journal</ref><ref name=Szesciorka_etal_2019>Template:Cite journal</ref> and seismic surveys as a part of oil and gas exploration.<ref name=DiIorio_Ckark_2009>Template:Cite journal</ref><ref name=McDonald_etal_1995>Template:Cite journal</ref> Blue whales in the Southern California Bight decreased calling in the presence of mid-frequency active (MFA) sonar.<ref name="Melcón_etal_2012">Template:Cite journal</ref> 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.<ref name=Southall_etal_2019>Template:Cite journal</ref>

The potential impacts of pollutants on blue whales is unknown. However, because blue whales feed low on the food chain, there is a lesser chance for bioaccumulation of organic chemical contaminants.<ref name=OShea_Brownell_1994>Template:Cite journal</ref> Analysis of the earwax of a male blue whale killed by a collision with a ship off the coast of California showed contaminants like pesticides, flame retardants, and mercury. Reconstructed persistent organic pollutant (POP) profiles suggested that a substantial maternal transfer occurred during gestation and/or lactation.<ref name=Trumble_etal_2013>Template:Cite journal</ref> Male blue whales in the Gulf of St. Lawrence, Canada, were found to have higher concentrations of PCBs, dichlorodiphenyltrichloroethane (DDT), metabolites, and several other organochlorine compounds relative to females, reflecting maternal transfer of these persistent contaminants from females into young.<ref name=Metcalfe_etal_2004>Template:Cite journal</ref>

See also

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

Further reading

• Template:Cite book
• {{#invoke:citation/CS1|citation

|CitationClass=web }}

• NOAA Fisheries, Office of Protected Resources Blue whale biology & status

External links

• Blue whale vocalizations – Cornell Lab of Ornithology—Bioacoustics Research Program (archived 26 February 2015)
• Blue whale video clips and news from the BBC – BBC Wildlife Finder
• Voices in the Sea – Sounds of the Blue Whale
• NOAA Stock Assessments
• Life of a Hunter: Blue Whale Template:Webarchive – BBC America
• Living With Predators – BBC America