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The blue whale (''Balaenoptera musculus'') is a
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can be of various shades of greyish-blue dorsally 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, ''B. m. indica'' in the Northern Indian Ocean. There is also 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 Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are consi ...
. They are generally solitary or gather in small groups, and have no well-defined social structure other than mother-calf bonds. The
fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. I ...
for blue whale vocalizations ranges from 8 to 25 Hz and the production of vocalizations may vary by region, season, behavior, and time of day.
Orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...
s are their only natural predators. The blue whale was once abundant in nearly all the Earth's oceans until the end of the 19th century. It was hunted almost to the point of
extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
by whalers until the
International Whaling Commission The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
banned all blue whale hunting in 1966. The
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
has listed blue whales as
Endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
as of 2018. It continues to face numerous man-made threats such as ship strikes, pollution, ocean noise and
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
.


Taxonomy


Nomenclature

The genus name, '' Balaenoptera'', means ''winged whale'' while the species name, ''musculus'', could mean "muscle" or a diminutive form of "mouse", possibly a pun by
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
when he named the species in '' Systema Naturae''. One of the first published descriptions of a blue whale comes from Robert Sibbald's ''Phalainologia Nova'', 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. Blue whales were referred to as 'Sibbald's rorqual', after Robert Sibbald, who first described the species.
Herman Melville Herman Melville ( born Melvill; August 1, 1819 – September 28, 1891) was an American novelist, short story writer, and poet of the American Renaissance period. Among his best-known works are ''Moby-Dick'' (1851); ''Typee'' (1846), a rom ...
called the blue whale "sulphur bottom" in his novel
Moby Dick ''Moby-Dick; or, The Whale'' is an 1851 novel by American writer Herman Melville. The book is the sailor Ishmael's narrative of the obsessive quest of Ahab, captain of the whaling ship ''Pequod'', for revenge against Moby Dick, the giant whi ...
because of the accumulation of
diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...
creating a yellowish appearance on their pale underside.


Evolution

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 The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
. The earliest discovered anatomically modern blue whale is a partial skull fossil found in southern
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, dating to the Early
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
, roughly 1.5–1.25 million years ago. 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, and New Zealand blue whales have an even lower genetic diversity. 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.


Hybridization

Blue whales are known to interbreed with
fin whale The fin whale (''Balaenoptera physalus''), also known as finback whale or common rorqual and formerly known as herring whale or razorback whale, is a cetacean belonging to the parvorder of baleen whales. It is the second-longest species of ce ...
s. The earliest description of a possible hybrid between a blue and fin whale was a anomalous female whale with the features of both the blue and the fin whales taken in the North Pacific. 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. Two live blue-fin whale hybrids have since been documented in the Gulf of St. Lawrence, (Canada), and in the Azores, (Portugal). 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; 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. Blue-fin hybrids have been detected from genetic analysis of whale meat samples taken from Japanese markets. Blue-fin whale hybrids are capable of being fertile. Molecular tests on a 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. There is reference to a humpback-blue whale hybrid in the South Pacific, attributed to marine biologist Michael Poole.


Subspecies and stocks

At least four subspecies of blue whale are recognized, some of which are divided into population stocks or "management units". They have a worldwide distribution, but are mostly absent from the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
and the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...
,
Okhotsk Okhotsk ( rus, Охотск, p=ɐˈxotsk) is an urban locality (a work settlement) and the administrative center of Okhotsky District of Khabarovsk Krai, Russia, located at the mouth of the Okhota River on the Sea of Okhotsk. Population: ...
, and Bering Sea. *Northern subspecies ('' B. m. musculus'') **North Atlantic population - This population is mainly documented from
New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York (state), New York to the west and by the Can ...
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 West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greate ...
, the
Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...
and northwest Africa. **Eastern North Pacific population - Whales in this region mostly feed off California from summer to fall and then Oregon, Washington State, the Alaska Gyre and
Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...
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. **Central/Western Pacific population - This stock is documented around the
Kamchatka Peninsula The Kamchatka Peninsula (russian: полуостров Камчатка, Poluostrov Kamchatka, ) is a peninsula in the Russian Far East, with an area of about . The Pacific Ocean and the Sea of Okhotsk make up the peninsula's eastern and w ...
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 The Gulf of Alaska (Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east ...
during fall and early winter. *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. *Pygmy blue whale ('' B. m. brevicauda'') **Madagascar population - This population migrates between the
Seychelles Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
and
Amirante Islands The Amirante Islands (''Les Amirantes'') are a group of coral islands and atolls that belong to the Outer Islands of the Seychelles. They stretch about 155 km from the African Banks (African Islands) in the north to Desnœufs (Isle des No ...
in the north and the Crozet Islands and
Prince Edward Island Prince Edward Island (PEI; ) is one of the thirteen provinces and territories of Canada. It is the smallest province in terms of land area and population, but the most densely populated. The island has several nicknames: "Garden of the Gulf", ...
s in the south were they feed, passing through the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about lon ...
. **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 The Great Australian Bight is a large oceanic bight, or open bay, off the central and western portions of the southern coastline of mainland Australia. Extent Two definitions of the extent are in use – one used by the International Hydrog ...
and Bass Strait. **Eastern Australia/New Zealand population - This stock may reside in the
Tasman Sea The Tasman Sea ( Māori: ''Te Tai-o-Rēhua'', ) is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer ...
and the Lau Basin in winter and feed mostly in the
South Taranaki Bight The South Taranaki Bight is a large bay on the west coast of New Zealand, south of Taranaki, west of the Manawatu, north and west of the western entrance of Cook Strait and north of the South Island. The name is sometimes used for a much smaller ...
and off the coast of eastern North Island. Blue whales have been detected around New Zealand throughout the year. *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. Blue whales off the
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
an coast may be a separate subspecies based on geographic separation, genetics, and unique song types. Chilean blue whales may overlap in the Eastern Tropical Pacific with
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
blue whales and Eastern North Pacific blue whales. Chilean blue whales are genetically differentiated from Antarctica blue whales and are unlikely to be
interbreeding In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in ...
. However, the genetic distinction is less with the Eastern North Pacific blue whale and there may be gene flow between hemispheres.


Description

The blue whale is a slender-bodied cetacean with a broad U-shaped head; thin, elongated flippers; a small 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. It has two blowholes that can squirt up in the air. The skin has a mottled grayish-blue coloration, appearing blue underwater. The mottling patterns near the
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
vary between individuals. The underbelly has lighter pigmentation and can appear yellowish due to
diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...
in the water, which historically earned them the nickname "sulphur bottom". The male blue whale has the largest penis in the animal kingdom, at around long and wide.


Size

The blue whale is the largest known animal to have ever existed. The
International Whaling Commission The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
(IWC) whaling database reports 88 individuals longer than , including one of , but problems with how the measurements were taken suggest that any longer than are suspect. The
Discovery Committee The Discovery Committee was a popular name for the Interdepartmental Committee for the Dependencies of the Falkland Islands established by the British Government to carry out scientific investigations (which became known as ‘Discovery Investigati ...
reported lengths up to ; however, the longest scientifically measured individual blue whale was from rostrum tip to tail notch. Female blue whales are larger than males. Hydrodynamic models suggest a blue whale could not exceed 108 ft (33 m) because of metabolic and energy constraints. The average length of sexually mature female blue whales is for Eastern North Pacific blue whales, for central and western North
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
blue whales, for North
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
blue whales, for Antarctic blue whales, for Chilean blue whales, and for pygmy blue whales. In the Northern Hemisphere, males weigh an average and females . Eastern North
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
blue whale males average and females . Antarctic males average and females . Pygmy blue whale males average to . The weight measured of the heart from a stranded North Atlantic blue whale was , the largest known in any animal. The record-holder blue whale was recorded at , with estimates of up to .


Life span

Blue whales live around 80–90 years or more. Scientists look at a blue whale's
earwax Earwax, also known by the medical term cerumen, is a brown, orange, red, yellowish or gray waxy substance secreted in the ear canal of humans and other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, ...
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. The maximum age of a pygmy blue whale determined this way is 73 years. In addition, female blue whales develop scars or corpora albicantia on their ovaries every time they ovulate. In a female pygmy blue whale, one corpus albicans is formed on average every 2.6 years.


Behavior

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. 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. The animals appear to use memory to locate the best feeding areas. 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. The traveling speed for blue whales ranges . The greatest dive depth reported from tagged blue whales was . Their theoretical aerobic dive limit was estimated at 31.2 minutes, however, the longest dive measured was 15.2 minutes. The deepest confirmed dive from a pygmy blue whale was . 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.


Diet and feeding

The blue whale's diet consists almost exclusively of
krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are consi ...
. Blue whales capture krill through lunge feeding, they swim towards them at high speeds as they open their mouths up to 80° They may engulf of water at one time. They squeeze the water out through their baleen plates with pressure from the throat pouch and tongue, and swallow the remaining krill. Blue whales have been recorded making 180° rolls during lunge-feeding, possibly allowing them to search the prey field and find the densest patches. 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. Blue whales have to engulf densities greater than 100 krill/m3 to maintain the cost of lunge feeding. They can consume from one mouthful of krill, which can provide up to 240 times more energy than used in a single lunge. It is estimated that an average-sized blue whale must consume of krill a day. Blue whales appear to avoid directly competing with other baleen whales. Different whale species select different feeding spaces and times as well as different prey species. In the
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
, baleen whales appear to feed on Antarctic krill of different sizes, which may lessen competition between them.


Reproduction and birth

Blue whales generally reach sexual maturity at 8–10 years. In the Northern Hemisphere, the length of which they reach maturity is for females and for males. In the Southern Hemisphere, the length of maturity is and for females and males respectively. Male pygmy blue whales average at sexual maturity. Female pygmy blue whales are in length and roughly 10 years old at the age of sexual maturity. Little is known about mating behavior, or breeding and birthing areas. Blue whales appear to be polygynous, with males competing for females. A male blue whale typically trails a female and will fight off potential rivals. The species mates from fall to winter. Pregnant females eat roughly four percent of their body weight daily, amounting to 60% of their overall body weight throughout summer foraging periods. Gestation may last 10–12 months with calves being long and weighing at birth. Estimates suggest that because calves require milk per kg of mass gain, blue whales likely produce of milk per day (ranging from of milk per day). The first video of a calf thought to be nursing was filmed in New Zealand in 2016. Calves may be
weaned Weaning is the process of gradually introducing an infant human or another mammal to what will be its adult diet while withdrawing the supply of its mother's milk. The process takes place only in mammals, as only mammals produce milk. The infan ...
when they reach 6–8 months old at a length of . They gain roughly during the weaning period. Interbirth periods last two to three years, they average 2.6 years in pygmy blue whales.


Vocalizations

Blue whales produce some of the loudest and lowest
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
vocalizations in the animal kingdom. and their inner ears appear well adapted for detecting low-frequency sounds. The
fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. I ...
for blue whale vocalizations ranges from 8 to 25 Hz. Blue whale songs vary between populations. 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"). A and B calls are often produced in repeated co-occurring sequences and sung only by males, suggesting a reproductive function. D calls may have multiple functions. They are produced by both sexes during social interactions while feeding. and by males when competing for mates. 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. A blue whale call recorded off Madagascar, a two‐unit phrase, consists of with 5–7 pulses with a
center frequency In electrical engineering and telecommunications, the center frequency of a filter or channel is a measure of a central frequency between the upper and lower cutoff frequencies. It is usually defined as either the arithmetic mean or the geometri ...
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. 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. Other vocalizations include 1–4 second long, frequency-modulated calls with a frequency of 80 and 38 Hz. There is evidence that some blue whale songs have temporally declined in tonal frequency. 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. The frequency of pygmy blue whales in the Antarctic has decreased by a few tenths of a hertz every year starting in 2002. It is possible that as blue whale populations recover from whaling, this is increasing sexual selection pressure (i.e., a lower frequency indicates a larger body size).


Predators and parasites

The only known natural threat to blue whales is the
orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...
, 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. 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. Documented
predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
by orcas has been rare. A blue whale mother and calf were first observed being chased at high speeds by orcas off southeastern Australia. The first documented attack occurred in 1977 off southwestern Baja California, Mexico, but the injured whale escaped after five hours. Four more blue whales were documented as being chased by a group of orcas between 1982 and 2003. The first documented predation event by orcas occurred September 2003, when a group of orcas in the Eastern Tropical Pacific was encountered feeding on a recently killed blue whale calf. In March 2014, a commercial whale watch boat operator recorded an incident involving a group of orcas harassing a blue whale in
Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area and its major city at the south of the bay, San Jose. San Francisco itself is further north along the coast, by ...
. The blue whale defended itself by slapping its tail. A similar incident was recorded by a drone in Monterey Bay in May 2017. 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 . 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. Other external parasites include barnacles such as ''
Coronula diadema ''Coronula diadema'' is a species of whale barnacle that lives on the skin of humpback whales and certain other species of whale. This species was first described by Carl Linnaeus in the 1767 12th edition of his ''Systema Naturae''. Description ...
'', ''
Coronula reginae ''Coronula'' is a genus of whale barnacles, containing the following species (those known only from the fossil record are marked '†'): *''Coronula aotea'' Fleming, 1959 † *''Coronula barbara'' Darwin, 1854 † *''Coronula bifida'' Bronn, 1831 ...
'' and ''
Cryptolepas rhachianecti ''Cryptolepas rhachianecti'' is a species of whale barnacle that lives as a Phoresis, passenger on the skin of gray whales and certain other species of whale in the northern Pacific Ocean. Description ''Cryptolepas rhachianecti'' can grow to a ...
'', which latch on their 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 ''Pennella balaenopterae'' is a large ectoparasitic copepod specialising in parasitising marine mammals. It is the largest member of the genus ''Pennella'', the other species of which are parasites of larger marine fish. Description ''P. ba ...
'' digs in and attaches itself to the blubber to feed on. Intestinal parasites include the
trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...
genera '' Ogmogaster'' and '' Lecithodesmus'', the
tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cesto ...
genera '' Priapocephalus'', '' Phyllobotrium'', '' Tetrabothrius'', '' Diphyllobotrium'' and '' Diplogonoporus'' and the
thorny-headed worm Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...
genus '' Bolbosoma''. In the North Atlantic, blue whales also contain the protozoans '' Entamoeba'', '' Giardia'' and '' Balantidium''.


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. 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 The International Convention for the Regulation of Whaling is an international environmental agreement aimed at the "proper conservation of whale stocks and thus make possible the orderly development of the whaling industry". It governs the comme ...
; this protection was extended to the Antarctic in 1965 and the North Pacific in 1966. The protected status of North Atlantic blue whales was not recognized by Iceland until 1960. In the US, the species is protected under the Endangered Species Act. Blue whales are formally classified as ''
endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
'' under both the US Endangered Species Act and the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
. They are also listed on Appendix I under the
Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of intern ...
(CITES) and the
Convention on the Conservation of Migratory Species of Wild Animals The Convention on the Conservation of Migratory Species of Wild Animals, also known as the Convention on Migratory Species (CMS) or the Bonn Convention, is an international agreement that aims to conserve migratory species throughout their r ...
. 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).


Threats

Blue whales were initially difficult to hunt because of their size and speed. This began to change in the mid-19th century with the development of harpoons that can be shot as projectiles. 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. The International Whaling Commission banned all hunting of blue whales in 1966 and gave them worldwide protection. However, the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
continued to illegally hunt blue whales and other species through to the 1970s. Ship strikes are a significant mortality factor for blue whales, especially off the U.S. West Coast, A total of 17 blue whales were killed or suspected to have been killed by ships between 1998 and 2019 off the US West Coast. Five deaths in 2007 off California were considered an unusual mortality event, as defined under the
Marine Mammal Protection Act The Marine Mammal Protection Act (MMPA) was the first act of the United States Congress to call specifically for an ecosystem approach to wildlife management. Authority MMPA was signed into law on October 21, 1972, by President Richard Nixon ...
. 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. Here, strikes caused the deaths of eleven blue whales in 2010 and 2012, and at least two in 2014. Ship strike mortality claimed the lives of two blue whales off southern Chile in the 2010s. 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. 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. Three more entanglement cases were reported in 2016. 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. Increasing
man-made Artificiality (the state of being artificial or manmade) is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity. Connotations Artificiality ...
underwater noise impacts blue whales. They may be exposed to noise from commercial shipping and seismic surveys as a part of oil and gas exploration. Blue whales in the Southern California Bight decreased calling in the presence of mid-frequency active (MFA)
sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...
. 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. The potential impacts of
pollutants A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...
on blue whales is unknown. However, because blue whales feed low on the
food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
, there is a lesser chance for bioaccumulation of organic chemical contaminants. 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 Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversel ...
(POP) profiles suggested that a substantial maternal transfer occurred during gestation and/or lactation. Male blue whales in the Gulf of St. Lawrence, Canada were found to have higher concentrations of PCBs,
dichlorodiphenyltrichloroethane Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
(DDT),
metabolites In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...
, and several other organochlorine compounds relative to females, reflecting maternal transfer of these persistent contaminants from females into young.


See also

*
List of cetaceans Cetacea is an infraorder that comprises the 94 species of whales, dolphins, and porpoises. It is divided into toothed whales (Odontoceti) and baleen whales (Mysticeti), which diverged from each other in the Eocene some 50 million years ago (m ...
*
List of largest mammals The following is a list of largest mammals by family. Tenrecs and allies (Afrosoricida) *The largest of these insectivorous mammals is the giant otter shrew (''Potamogale velox''), native to Central Africa. This species can weigh up to and mea ...
*
List of whale vocalizations Whale vocalizations are the sounds made by whales to communicate. The word "song" is used in particular to describe the pattern of regular and predictable sounds made by some species of whales (notably the humpback) in a way that is reminiscent ...


References


Further reading

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


External links


Blue whale vocalizations
– Cornell Lab of Ornithology—Bioacoustics Research Program
Blue whale video clips and news from the BBC – BBC Wildlife Finder



NOAA Stock Assessments

Life of a Hunter: Blue Whale
– BBC America
Living With Predators
– BBC America {{Authority control
Blue whales The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
Mammals described in 1758 Conservation-reliant species Cosmopolitan mammals Biological records ESA endangered species Taxa named by Carl Linnaeus