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Riga 1:
{{Tassobox
|
|nome=Balenottera azzurra <ref name=MSW3>{{MSW3|id=14300018}}</ref>
|statocons=EN
|statocons_versione=iucn3.1
|statocons_ref=<ref name="iucn">{{IUCN|summ=2477|autore=Taylor, B.L. & Notarbartolo di Sciara, G. (Cetacean Red List Authority) 2008}}</ref>
|immagine=[[Immagine:Bluewhale877.jpg|230px]]
[[
|didascalia=
<!-- CLASSIFICAZIONE: -->
|dominio=
Riga 19 ⟶ 20:
<!-- PER TUTTI: -->
|superclasse=
|classe=[[
|sottoclasse=
|infraclasse=
|superordine=
|ordine=[[Cetacea]]
|sottordine=[[Mysticeti]]
Riga 48 ⟶ 49:
|nomicomuni=
|suddivisione=[[Areale]]
|suddivisione_testo=[[
* ''B. m. musculus'' <small>Linnaeus, 1758</small>
* ''[[Balaenoptera musculus brevicauda|B. m. brevicauda]]'' <small>Ichihara, 1966</small>
* ''B. m. indica'' <small>Blyth, 1859</small>
* ''B. m. intermedia'' <small>Burmeister, 1871</small>
}}
La '''balenottera azzurra''' ('''''Balaenoptera musculus''
| url=http://nationalzoo.si.edu/Animals/AnimalRecords/
| title=Animal Records
| publisher=Smithsonian National Zoological Park
| accessdate=2007-05-29 }}</ref> di peso, è il più grande animale conosciuto mai vissuto sul Pianeta <ref>{{cite web
| url=http://science.howstuffworks.com/question687.htm
| title=What is the biggest animal ever to exist on Earth?
| publisher=How Stuff Works
| accessdate=2007-05-29}}</ref> .
Lungo e slanciato, il corpo della balenottera azzurra può assumere varie tonalità grigio-bluastre sul dorso, ma si fa più chiaro sul ventre <ref>[http://www.fao.org/fishery/species/2744 FI - Species fact sheets.] Fisheries and Aquaculture Department, Food and Agriculture Organization.</ref> . Ne esistono almeno tre [[sottospecie]] riconosciute: ''B. m. musculus'' dell'Atlantico e del Pacifico settentrionali, ''B. m. intermedia'' dell'[[Mari antartici|Oceano Australe]], ''B. m. brevicauda'' (nota anche come [[Balaenoptera musculus brevicauda|balenottera azzurra pigmea]]) dell'[[Oceano Indiano]] e del [[Oceano Pacifico|Pacifico meridionale]] e ''B. m. indica'', anch'essa dell'Oceano Indiano. Come quella degli altri Misticeti, anche la sua dieta consiste quasi esclusivamente dei piccoli [[crostacei]] noti come [[krill]] <ref name="wheelock">{{cite web
|url=http://whale.wheelock.edu/bwcontaminants/welcome.html
|title=Contaminant analysis of organochlorines in blubber biopsies from blue whales in the St Lawrence
|publisher=Trent University
|author=Jason de Koning and Geoff Wild
|year=1997
| accessdate = 2007-06-29}}</ref> .
Fino agli inizi del XX secolo la balenottera azzurra era numerosa in quasi tutti gli oceani. Per più di 40 anni, però, è stata cacciata dai [[Caccia alla balena|balenieri]] fin quasi all'[[estinzione]]; la comunità internazionale la dichiarò specie protetta solamente nel 1966. Secondo un rapporto del 2002 in tutto il mondo vi sarebbero attualmente dai 5000 ai 12.000 esemplari <ref name=pop>{{cite web
|url=http://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_blue_whale_e.pdf
|publisher=Committee on the Status of Endangered Wildlife in Canada
|year=2002
|title=Assessment and Update Status Report on the Blue Whale ''Balaenoptera musculus''
| accessdate = 2007-04-19
|format=PDF}}</ref>, suddivisi in almeno cinque gruppi. In base a ricerche più recenti effettuate sulla sottospecie pigmea si ipotizza che tali numeri, però, siano stati un po'troppo sottostimati <ref name=BBC_pop>{{Cite web
| author=Alex Kirby|work= BBC News
| title=Science seeks clues to pygmy whale
| url=http://news.bbc.co.uk/2/hi/science/nature/3003564.stm
| accessdate=April 21, 2006 | date=2003-06-19}}</ref> . Prima della caccia, la popolazione più numerosa era quella antartica, forte di circa 239.000 esemplari (le stime vanno da 202.000 a 311.000) <ref name = Ant>{{cite journal
| title = Evidence for increases in Antarctic blue whales based on Bayesian modelling
| author = T.A. Branch, K. Matsuoka and T. Miyashita
| journal = Marine Mammal Science
| volume = 20
| pages = 726–754
|year = 2004
| doi = 10.1111/j.1748-7692.2004.tb01190.x}}</ref> . Ora rimangono solo popolazioni molto più piccole (di circa 2000 esemplari l'una), concentrate nel [[Oceano Pacifico|Pacifico]] nord-orientale e negli oceani [[Mari antartici|Australe]] e [[Oceano Indiano|Indiano]]. Due popolazioni meno numerose si incontrano nell'[[Oceano Atlantico|Atlantico]] settentrionale ed almeno altre due nell'[[emisfero australe]].
==Tassonomia==
{{See also|Evoluzione dei cetacei}}
La balenottera azzurra appartiene alla famiglia dei [[Balaenopteridae|Balenotteridi]], un gruppo che comprende la [[megattera]], la [[balenottera comune]], la [[balenottera di Bryde]], la [[balenottera boreale]] e la [[balenottera minore]] <ref name="factsheet" /> . Si ritiene che i [[Balaenopteridae|Balenotteridi]] si siano separati dalle altre famiglie del sottordine dei [[Mysticeti|Misticeti]] non più tardi dell'[[Oligocene]] Medio. However, it is not known when the members of those families diverged from each other.
The blue whale is usually classified as one of eight species in the genus ''Balaenoptera''; one authority places it in a separate monotypic genus, ''Sibbaldus'',<ref>{{cite book
| author= Barnes LG, McLeod SA.
|editor= Jones ML et al.
|title= The Gray Whale
|year= 1984
|publisher= Academic Press
|___location= Orlando, Florida
| isbn = 0123891809
|pages=3–32
|chapter= The fossil record and phyletic relationships of gray whales.}}</ref> but this is not accepted elsewhere.<ref name=msw3/> [[DNA]] sequencing analysis indicates that the blue whale is [[phylogenetics|phylogenetically]] closer to the [[sei whale]] (''Balaenoptera borealis'') and [[Bryde's whale]] (''Balaenoptera brydei'') than to other ''Balaenoptera'' species, and closer to the [[humpback whale]] (''Megaptera'') and the [[gray whale]] (''Eschrichtius'') than to the [[minke whale]]s (''Balaenoptera acutorostrata'' and ''Balaenoptera bonaerensis'').<ref>{{cite journal
|title=Cetacean mitochondrial DNA control region: sequences of all extant baleen whales and two sperm whale species
|author=Arnason, U., Gullberg A. & Widegren, B.
|journal=Molecular Biology and Evolution
|volume=10
|pages=960–970
|date= September 1, 1993 |url=http://mbe.oxfordjournals.org/cgi/content/abstract/10/5/960
|accessdate=2009-01-25
|pmid=8412655
|issue=5
}}</ref><ref>{{cite journal
|title=Mitochondrial Phylogenetics and Evolution of Mysticete Whales
|author=Sasaki, T
|journal=Systematic Biology
|volume=54
|issue=1
|pages=77–90
|date=February 23, 2005
|doi=10.1080/10635150590905939
|url=http://www.informaworld.com/smpp/content~content=a716097098~db=all
|accessdate=2009-01-25
|pmid=15805012
|last2=Nikaido
|first2=M
|last3=Hamilton
|first3=H
|last4=Goto
|first4=M
|last5=Kato
|first5=H
|last6=Kanda
|first6=N
|last7=Pastene
|first7=L
|last8=Cao
|first8=Y
|last9=Fordyce
|first9=R}}</ref> If further research confirms these relationships, it will be necessary to reclassify the rorquals.
There have been at least 11 documented cases of blue/[[Fin whale|fin]] hybrid adults in the wild. Arnason and Gullberg describe the genetic distance between a Blue and a Fin as about the same as that between a human and a gorilla.<ref>{{cite journal
| author = A. Arnason and A. Gullberg
| title = Comparison between the complete mtDNA sequences of the blue and fin whale, two species that can hybridize in nature
| journal = Journal of Molecular Ecology
| year = 1993
| volume = 37
|pages = 312–322}}</ref> Researchers working off of Fiji believe they photographed a hybrid [[Humpback whale|humpback]]/blue whale.<ref>[http://www.whalecenter.org/amazarch.htm Amazing Whale Facts Archive]. Whale Center of New England (WCNE). Retrieved on 2008-02-27.</ref>
The specific name ''musculus'' is [[Latin]] and could mean "muscular", but it can also be interpreted as "little mouse".<ref>{{cite book
| last = Simpson
| first = D.P.
| title = Cassell's Latin Dictionary
| publisher = Cassell Ltd.
| year = 1979
| edition = 5
| ___location = London
| page = 883
| isbn = 0-304-52257-0}}</ref> [[Carolus Linnaeus|Linnaeus]], who named the species in his seminal ''[[Systema Naturae]]'' of 1758,<ref>{{la icon}} {{cite book
| last=Linnaeus
| first=C
| authorlink=Carolus Linnaeus
| title=Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
| publisher=Holmiae. (Laurentii Salvii).
| year=1758
| page=824
| url= }}</ref> would have known this and may have intended the ironic [[double entendre|double meaning]].<ref>{{cite web
|url=http://www.dec.ny.gov/animals/9367.html
|title=Blue Whale Fact Sheet
|publisher=New York State Department of Environmental Conservation
| accessdate = 2007-06-29}}</ref> [[Herman Melville]] called this species '''sulphur-bottom''' in his novel ''[[Cetology of Moby-Dick|Moby-Dick]]'' due to an orange-brown or yellow tinge on the underparts from [[diatom]] films on the skin. Other common names for the blue whale have included the '''Sibbald's rorqual''' (after [[Robert Sibbald|Sir Robert Sibbald]]), the '''great blue whale''' and the '''great northern rorqual'''. These names have now fallen into disuse.
Authorities classify the species into three or four subspecies: ''B. m. musculus'', the [[northern blue whale]] consisting of the North Atlantic and North Pacific populations, ''B. m. intermedia'', the [[southern blue whale]] of the [[Southern Ocean]], ''B. m. brevicauda'', the [[pygmy blue whale]] found in the Indian Ocean and South Pacific,<ref>Ichihara T. (1966). The pygmy blue whale ''B. m. brevicauda'', a new subspecies from the Antarctic in ''Whales, dolphins and porpoises'' Page(s) 79-113.</ref> and the more problematic ''B. m. indica'', the [[Great Indian Rorqual]], which is also found in the Indian Ocean and, although described earlier, may be the same subspecies as ''B. m. brevicauda''.<ref name=msw3/>
==Description and behaviour==
[[Image:Blue_whale_tail.JPG|thumb|left|A blue whale lifting its tail flukes.]]
[[Image:Blue Whale 001 body bw.jpg|thumb|Adult blue whale]]
[[Image:Bl-4.JPG|thumb|Aerial view of a blue whale showing both pectoral fins]]
[[Image:Bluewhale 300.jpg|right|thumb|The blow of a blue whale]]
[[Image:Bl-10 blue.jpg|thumb|The small [[dorsal fin]] of this blue whale is just visible on the far left.]]
The blue whale has a long tapering body that appears stretched in comparison with the stockier build of other whales.<ref name="des" /> The head is flat and ''U''-shaped and has a prominent ridge running from the [[Blowhole (biology)|blowhole]] to the top of the upper lip.<ref name="des" /> The front part of the mouth is thick with [[baleen]] plates; around 300 plates (each around one metre (3.2 ft) long)<ref name="des" /> hang from the upper jaw, running 0.5 m (1.6 ft) back into the mouth. Between 60 and 90 grooves (called ventral pleats) run along the throat parallel to the body length. These pleats assist with evacuating water from the mouth after lunge feeding (see feeding below).
The [[dorsal fin]] is small,<ref name="des" /> visible only briefly during the dive sequence. Located around three-quarters of the way along the length of the body, it varies in shape from one individual to another; some only have a barely perceptible lump, but others may have prominent and [[falcate]] dorsals. When surfacing to breathe, the blue whale raises its shoulder and blowhole out of the water to a greater extent than other large whales such as the [[Fin whale|fin]] or [[Sei whale|sei]]. Observers can use this trait to differentiate between species at sea. Some blue whales in the North Atlantic and North Pacific raise their tail fluke when diving. When breathing, the whale emits a spectacular vertical single-column spout up to {{convert|12|m|ft}}, typically {{convert|9|m|ft}}. Its [[lung]] capacity is 5,000 litres (1320 U.S. gallons). Blue whales have twin blowholes shielded by a large splashguard.<ref name="des" />
The flippers are {{convert|3|-|4|m|ft}} long. The upper sides are grey with a thin white border. The lower sides are white. The head and tail fluke are generally uniformly grey. The whale's upper parts, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform slate-grey color, but others demonstrate a considerable variation of dark blues, greys and blacks, all tightly mottled.<ref name="factsheet">{{citeweb
|url=http://www.acsonline.org/factpack/bluewhl.htm
|title=American Cetacean Society Fact Sheet - Blue Whales
|accessdate=20 June 2007
}}</ref>
Blue whales can reach speeds of {{convert|50|km/h|mph}} over short bursts, usually when interacting with other whales, but {{convert|20|km/h|mph}} is a more typical traveling speed.<ref name="factsheet" /> When feeding, they slow down to {{convert|5|km/h|mph}}.
Blue whales most commonly live alone or with one other individual. It is not known how long traveling pairs stay together. In locations where there is a high concentration of food, as many as 50 blue whales have been seen scattered over a small area. However, they do not form the large close-knit groups seen in other baleen species.
===Size===
[[Image:Joey williams with a 19 foot long blue whale skull.jpg|thumb|A 19-foot-long blue whale [[skull]] in the collections of the [[Smithsonian Museum of Natural History]].]]
Blue whales are difficult to weigh because of their size. Most blue whales killed by whalers were not weighed whole, but cut up into manageable pieces first. This caused an underestimate of the total weight of the whale, due to the loss of blood and other fluids. Nevertheless, measurements between {{convert|150|-|170|metric ton |short ton}} were recorded of animals up to {{convert|27|m|ft}} in length. The weight of an individual {{convert|30|m|ft}} long is believed by the American [[National Marine Mammal Laboratory]] (NMML) to be in excess of {{convert|180|metric ton|short ton}}. The largest blue whale accurately weighed by NMML scientists to date was a female that weighed {{convert|177|metric ton|short ton}}.<ref name=pop />
The blue whale is the largest animal ever known to have lived.<ref name="des">{{citeweb
|url=http://www.wdcs.org/dan/publishing.nsf/allweb/F8FE8974A62E12F88025696D004A8EE9
|title=Size and Description of the Blue Whale Species
|accessdate=15 June 2007
}}</ref> The largest known [[dinosaur]] of the [[Mesozoic]] Era was the ''[[Argentinosaurus]]'',<ref>{{es icon}} {{cite journal
|author= Bonaparte J, Coria R
|year= 1993
|title=Un nuevo y gigantesco sauropodo titanosaurio de la Formacion Rio Limay (Albiano-Cenomaniano) de la Provincia del Neuquen, Argentina
|journal= Ameghiniana
|volume=30
|issue= 3
|pages=271–282}}</ref> which is estimated to have weighed up to {{convert|90|metric ton|short ton}}, though a controversial vertebra of ''[[Amphicoelias]] fragillimus'' may indicate an animal of up to {{convert|122|metric ton|short ton}} and {{convert|40|-|60|m|ft}}.<ref name="carpenter2006">Carpenter, K. (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod ''Amphicoelias fragillimus''." In Foster, J.R. and Lucas, S.G., eds., 2006, ''Paleontology and Geology of the Upper Jurassic Morrison Formation.'' New Mexico Museum of Natural History and Science Bulletin '''36''': 131-138.[https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/Amphicoelias.pdf]</ref> Furthermore, there are weight estimates for the very poorly known ''[[Bruhathkayosaurus]]'' ranging from {{convert|140|-|220|metric ton|short ton}}, besides length estimates up to about {{convert|45|m|ft}}. The extinct fish [[Leedsichthys]] may have approached its size.<ref>{{cite web
|url=http://news.nationalgeographic.com/news/2003/10/1001_031001_biggestfish.html
|title="Biggest Fish Ever Found" Unearthed in U.K
|publisher=News.nationalgeographic.com
|date=October 1, 2003
|accessdate=2008-11-03}}</ref> However, complete fossils are difficult to come by, making size comparisons difficult. All these animals are considered to be smaller than the blue whale.
There is some uncertainty about the biggest blue whale ever found, as most data comes from blue whales killed in [[Antarctica|Antarctic]] waters during the first half of the twentieth century and was collected by whalers not well-versed in standard zoological measurement techniques. The longest whales ever recorded were two females measuring {{convert|33.6|-|33.3|m|ft}} respectively.<ref name = "SearsCal02">{{cite paper
| author = Sears R, Calambokidis J
| title = Update COSEWIC status report on the blue whale Balaenoptera musculus in Canada.
| publisher = Committee on the Status of Endangered Wildlife in Canada, Ottawa.
| year = 2002
| pages = 32}}</ref> The longest whale measured by [[scientist]]s at the NMML was {{convert|29.9|m|ft}}.<ref name=pop />
A blue whale's [[tongue]] weighs around {{convert|2.7|metric ton|short ton}}<ref name="SM">{{cite book
|title=The Scientific Monthly
|publisher=American Association for
the Advancement of Science
|year=1915
|page=21}}</ref> and, when fully expanded, its mouth is large enough to hold up to {{convert|90|metric ton|short ton}} of food and water.<ref name="wheelock" /> Despite the size of its mouth, the dimensions of its throat are such that a blue whale cannot swallow an object wider than a beach ball.<ref>Blue Planet: Frozen seas (BBC documentary)</ref> Its [[heart]] weighs {{convert|600|kg|lb}} and is the [[largest body part|largest]] known in any animal.<ref name="SM" /> A blue whale's [[aorta]] is about {{convert|23|cm|in}} in diameter.<ref>{{cite web
|url=http://www2.ucsc.edu/seymourcenter/PDF/2.%20Ms.%20B%20measurements.pdf
|title=Ms. Blue's Measurements
|author=Caspar, Dave
|year=2001
| month=April
|accessdate=2006-09-01
|publisher=Seymour Center, University of California, Santa Cruz.
|format=PDF}}</ref> During the first seven months of its life, a blue whale calf drinks approximately 400 litres (100 U.S. gallons) of milk every day. Blue whale calves gain [[body weight|weight]] quickly, as much as {{convert|90|kg|lb}} every 24 hours. Even at birth, they weigh up to {{convert|2700|kg|lb}}—the same as a fully grown [[hippopotamus]].<ref name="factsheet" />
===Feeding===
Blue whales feed almost exclusively on [[krill]], though they also take small numbers of [[copepods]].<ref name="afsc">{{cite web
|url=http://www.afsc.noaa.gov/nmml/education/cetaceans/blue.php
|title=Detailed Information about Blue Whales
|publisher=Alaska Fisheries Science Center
|year=2004
| accessdate = 2007-06-14}}</ref> The species of this [[zooplankton]] eaten by blue whales varies from ocean to ocean. In the North Atlantic, ''[[Meganyctiphanes norvegica]]'', ''[[Thysanoessa raschii]]'', ''[[Thysanoessa inermis]]'' and ''[[Thysanoessa longicaudata]]'' are the usual food;<ref>{{cite journal
|author= Hjort J, Ruud JT
|year=1929
|title=Whaling and fishing in the North Atlantic
|journal= Rapp. Proc. Verb. Conseil int. Explor. Mer
|volume= 56
|issue=
|pages= }}</ref><ref>{{cite journal
|author=Christensen I, Haug T, Øien N
|year=1992
|title= A review of feeding and reproduction in large baleen whales (Mysticeti) and sperm whales ''Physeter macrocephalus'' in Norwegian and adjacent waters
|journal= Fauna Norvegica Series a
|volume= 13
|issue=
|pages=39–48}}</ref><ref>{{cite journal
|author= Sears R, Wenzel FW, Williamson JM
|year=1987
|title=The Blue Whale: A Catalogue of Individuals from the Western North Atlantic (Gulf of St. Lawrence)
|journal=Mingan Island Cetacean Study, St. Lambert, Quebec.
|pages=27}}</ref> in the North Pacific, ''[[Euphausia pacifica]]'', ''[[Thysanoessa inermis]]'', ''[[Thysanoessa longipes]]'', ''[[Thysanoessa spinifera]]'', ''[[Nyctiphanes symplex]]'' and ''[[Nematoscelis megalops]]'';<ref>{{cite journal
|last=Sears
|first=R
|year=1990
|title= The Cortez blues
|journal= Whalewatcher
|volume=24
|issue=2
|pages=12–15}}</ref><ref>{{cite journal
|last=Kawamura
|first=A
|year= 1980
|title= A review of food of balaenopterid whales
|journal= Sci. Rep. Whales Res. Inst.
|volume=32
|issue=
|pages=155–197}}</ref><ref>{{cite book
|author=Yochem PK, Leatherwood S
|editor=Ridgway SH, Harrison R
|title= Handbook of Marine Mammals, Vol. 3:The Sirenians and Baleen Whales.
|edition=
|year=1980
|publisher=Academic Press
|___location=London
|isbn=
|oclc=
|doi=
|id=
|pages= 193–240
|chapter= Blue whale ''Balaenoptera musculus'' (Linnaeus, 1758)}}</ref> and in the Antarctic, ''[[Euphausia superba]]'', ''[[Euphausia crystallorophias]]'' and ''[[Euphausia valentin]]''.
An adult blue whale can eat up to 40 million krill in a day.<ref>[http://afp.google.com/article/ALeqM5j16BZVAVoE3Tey_0icx_2Bj6V_XQ Afp.google.com Hunted, rammed, poisoned, whales may die from heartbreak too]</ref> The whales always feed in the areas with the highest concentration of krill, sometimes eating up to {{convert|3600|kg|lb}} of krill in a single day.<ref name="afsc" /> This daily calorie requirement of an adult blue whale is in the region of 1.5 million.<ref>[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press]].</ref>
Because krill move, blue whales typically feed at depths of more than {{convert|100|m|ft}} during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 20 minutes are common. The longest recorded dive is 36 minutes<ref name=Sears98>(Sears 1998)</ref>. The whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. The blue whale also incidentally consumes small fish, crustaceans and squid caught up with krill.<ref>{{cite journal
|author= Nemoto T
|year=1957
|title=Foods of baleen whales in the northern Pacific
|journal= Sci. Rep. Whales Res. Inst.
|volume=12
|pages=33–89}}</ref><ref>{{cite journal
|author=Nemoto T, Kawamura A
|year=1977
|title= Characteristics of food habits and distribution of baleen whales with special reference to the abundance of North Pacific sei and Bryde’s whales
|journal=Rep. Int. Whal. Commn
|volume= 1
|issue=Special Issue
|pages=80–87}}</ref>
===Life history===
[[Image:BlueWhaleWithCalf.jpg|thumb|A juvenile blue whale with its mother]]
Mating starts in late autumn and continues to the end of winter.<ref name="Art">{{citeweb
|url=http://www.articleworld.org/index.php/Blue_Whale
|title=Blue Whale - ArticleWorld
|accessdate=2 July 2007
}}</ref> Little is known about mating behaviour or breeding grounds. Females typically give birth once every two to three years at the start of the winter after a [[gestation period]] of ten to twelve months.<ref name="Art" /> The calf weighs about {{convert|2.5|metric ton|short ton}} and is around {{convert|7|m|ft}} in length. Blue whale calves drink 380–570 litres (100–150 U.S. gallons) of milk a day. [[Weaning]] takes place for about six months, by which time the calf has doubled in length. Sexual maturity is typically reached at eight to ten years, by which time males are at least {{convert|20|m|ft}} long (or more in the Southern Hemisphere). Females are larger still, reaching sexual maturity at around the age of five, by which they are about {{convert|21|m|ft}} long.
Scientists estimate that blue whales can live for at least 80 years;<ref name = "SearsCal02"/><ref name="Art" /><ref name="npca">{{citeweb
|url=http://www.npca.org/marine_and_coastal/marine_wildlife/bluewhale.html
|title=www.npca.org
|accessdate=21 June 21, 2007
}}</ref> however, since individual records do not date back into the whaling era, this will not be known with certainty for many years. The longest recorded study of a single individual is 34 years, in the north-east Pacific.<ref name=Sears98/> The whales' only natural predator is the [[Orca]].<ref>{{cite journal
| title = Sightings and movements of blue whales off central California from 1986–88 from photo-identification of individuals
| author = J. Calambokidis, G. H. Steiger, J. C. Cubbage, K. C. Balcomb, C. Ewald, S. Kruse, R. Wells and R. Sears
| journal = Rep. Whal. Comm.
| volume = 12
| pages = 343–348
| year = 1990}}</ref> Studies report that as many as 25% of mature blue whales have scars resulting from Orca attacks.<ref name = "SearsCal02"/> The mortality rate of such attacks is unknown.
Blue whale strandings are extremely uncommon, and, because of the species' social structure, mass strandings are unheard of.<ref>William Perrin and Joseph Geraci. "Stranding" pp 1192–1197 in ''Encyclopedia of Marine Mammals'' (Perrin, Wursig and Thewissen eds)</ref> However, when strandings do occur, they can become the focus of public interest. In 1920, a blue whale washed up near [[Bragar]] on the [[Isle of Lewis]] in the [[Outer Hebrides]] of [[Scotland]]. It had been shot in the head by whalers, but the harpoon had failed to explode. As with other mammals, the fundamental instinct of the whale was to try to carry on breathing at all costs, even though this meant beaching to prevent itself from drowning. Two of the whale's bones were erected just off a main road on Lewis and remain a tourist attraction.<ref>{{cite web
| title=The Whale bone Arch
| work = Places to Visit around the Isle of Lewis
| url=http://www.isle-of-lewis.com/places-to-visit.htm
| accessdate = 2005-05-18}}</ref>
===Vocalizations===
{{See also|Whale song}}
{| class="infobox" style="" width="25%"
|- style="text-align: center;"
|'''Multimedia relating to the blue whale'''<br /><div class="small">''Note that the whale calls have been sped up 10x from their original speed.''</div>
|-
|{{listen
| filename = Blue whale atlantic1.ogg
| title = A blue whale song
| description = Recorded in the Atlantic (1)
| format = [[Ogg]]
| filename2 = Blue whale atlantic2.ogg
| title2 = A blue whale song
| description2 = Recorded in the Atlantic (2)
| format2 = [[Ogg]]
| filename3 = Blue whale atlantic3.ogg
| title3 = A blue whale song
| description3 = Recorded in the Atlantic (3)
| format3 = [[Ogg]]
| filename4 = Blue_Whale_NE_Pacific.ogg
| title4 = A blue whale song
| description4 = Recorded in North Eastern Pacific
| format4 = [[Ogg]]
| filename5 = Blue_Whale_South_Pacific.ogg
| title5 = A blue whale song
| description5 = Recorded in the South Pacific
| format5 = [[Ogg]]
| filename6 = Blue_Whale_West_Pacific.ogg
| title6 = A blue whale song
| description6 = Recorded in the West Pacific
| format6 = [[Ogg]]
}}
|}
Estimates made by Cummings and Thompson (1971) suggest that source level of sounds made by blue whales are between 155 and 188 [[decibel]]s when measured relative to a reference pressure of one [[micropascal]] at one metre.<ref>{{cite journal
| title = Underwater sounds from the blue whale ''Balaenoptera musculus''
| author = W.C. Cummings and P.O. Thompson
| journal = Journal of the Acoustics Society of America
| volume = 50(4)
| pages = 1193–1198
| year = 1971
| doi = 10.1121/1.1912752}}</ref><ref>{{cite book
| author= W.J. Richardson, C.R. Greene, C.I. Malme and D.H. Thomson
| title = Marine mammals and noise
| publisher = Academic Press, Inc., San Diego, CA.
| year = 1995
| isbn = 0-12-588441-9}}</ref> All blue whale groups make calls at a [[fundamental frequency]] of between 10 and 40 [[Hertz|Hz]]; the lowest frequency sound a human can typically perceive is 20 Hz. Blue whale calls last between ten and thirty seconds. Blue whales off the coast of [[Sri Lanka]] have been repeatedly recorded making "songs" of four notes duration lasting about two minutes each, reminiscent of the well-known [[whale song|humpback whale songs]]. Researchers believe that as this phenomenon has not been seen in any other populations, it may be unique to the ''B. m. brevicauda'' (Pygmy) subspecies.
The reason for vocalization is unknown. Richardson ''et al.'' (1995) discuss six possible reasons:<ref>{{cite web
| author = National Marine Fisheries Service
| year = 2002
| title = Endangered Species Act - Section 7 Consultation Biological Opinion
| url = http://www.nmfs.noaa.gov/prot_res/readingrm/ESAsec7/7pr_surtass-2020529.pdf
| format = PDF }}</ref>
# Maintenance of inter-individual distance
# Species and individual recognition
# Contextual information transmission (e.g., feeding, alarm, courtship)
# Maintenance of social organization (e.g., contact calls between females and males)
# Location of topographic features
# Location of prey resources
==Population and whaling==
===Hunting era===
{{Main|History of whaling}}
[[Image:Blue Whale population, Pengo.svg|thumb|400px|Blue whale populations have declined dramatically due to commercial whaling.]]
Blue whales are not easy to catch or kill. Their speed and power meant that they were rarely pursued by early whalers, who instead targeted [[Sperm whale|sperm]] and [[right whale]]s.<ref>{{cite book
|author= Scammon CM
|title=The marine mammals of the northwestern coast of North America. Together with an account of the American whale-fishery
|year= 1874
|publisher=John H. Carmany and Co.
|___location=San Francisco
|page=319
|isbn= }}</ref> In 1864, the Norwegian [[Svend Foyn]] equipped a [[steamboat]] with [[harpoon]]s specifically designed for catching large whales.<ref name="factsheet" /> Although initially cumbersome and with a low success rate, Foyn perfected the harpoon gun, and soon several whaling stations were established on the coast of [[Finnmark]] in northern [[Norway]]. Because of disputes with the local fishermen, the last whaling station in Finnmark was closed down in 1904.
Soon, blue whales were being hunted in [[Iceland]] (1883), the [[Faroe Islands]] (1894), [[Newfoundland (island)|Newfoundland]] (1898), and [[Spitsbergen]] (1903). In 1904-05 the first blue whales were taken off [[South Georgia]]. By 1925, with the advent of the stern slipway in factory ships and the use of steam-driven whale catchers, the catch of blue whales, and baleen whales as a whole, in the Antarctic and sub-Antarctic began to increase dramatically. Between 1930 and 1931, these ships killed 29,400 blue whales in the Antarctic alone. By the end of [[World War II]], populations had been significantly depleted, and, in 1946, the first quotas restricting international trade in whales were introduced, but they were ineffective because of the lack of differentiation between species. Rare species could be hunted on an equal footing with those found in relative abundance.
Blue whale hunting was banned in the 1960s by the [[International Whaling Commission]],<ref>{{cite journal
|last=Gambell
|first=R
|year= 1979
|title=The blue whale
|journal= Biologist
|volume= 26
|pages=209–215}}</ref><ref>{{cite journal
|last=Best
|first=PB
|year=1993
|month=
|title=Increase rates in severely depleted stocks of baleen whales
|journal=ICES J. Mar. Sci.
|volume=50
|pages=169–186
|doi=10.1006/jmsc.1993.1018}}</ref> and illegal whaling by the USSR finally halted in the 1970s,<ref>{{cite journal
|last=Yablokov
|first=AV
|year=1994
|title=Validity of whaling data
|journal=Nature
|volume=367
|issue=
|pages=108
|doi=10.1038/367108a0}}</ref> by which time 330,000 blue whales had been killed in the Antarctic, 33,000 in the rest of the Southern Hemisphere, 8,200 in the North Pacific, and 7,000 in the North Atlantic. The largest original population, in the Antarctic, had been reduced to 0.15% of their initial numbers.<ref name=Ant/>
===Population and distribution today===
[[Image:Blauwal01.jpg|thumb|A blue whale set against the backdrop of the [[Azores]]]]
[[Image:Blue whale tail fluke.JPG|thumb|Image of a blue whale's tail fluke with the [[Santa Barbara Channel Islands]] in the background, August 2007]]
Since the introduction of the whaling ban, studies have failed to ascertain whether the [[conservation reliant species|conservation reliant]] global blue whale population is increasing or remaining stable. In the Antarctic, best estimates show a significant increase at 7.3% per year since the end of illegal Soviet whaling, but numbers remain at under 1% of their original levels.<ref name=Ant/> It has also been suggested that Icelandic and Californian populations are increasing but these increases are not statistically significant. The total world population was estimated to be between 5,000 and 12,000 in 2002, although there are high levels of uncertainty in available estimates for many areas.<ref name=pop/>
The [[IUCN Red List]] counts the blue whale as "endangered" as it has since the list's inception. In the [[United States]], the [[National Marine Fisheries Service]] lists them as endangered under the [[Endangered Species Act]].<ref>{{cite web
|url=http://www.nmfs.noaa.gov/pr/laws/esa/
|title=Endangered Species Act
}}</ref> The largest known concentration, consisting of about 2,000 individuals, is the North-East Pacific population of the Northern blue whale (''B. m. musculus'') subspecies that ranges from [[Alaska]] to [[Costa Rica]] but is most commonly seen from California in summer. Infrequently, this population visits the North-West Pacific between [[Kamchatka Peninsula|Kamchatka]] and the northern tip of Japan.
In the North Atlantic, two stocks of ''B. m. musculus'' are recognized. The first is found off [[Greenland]], [[Newfoundland and Labrador|Newfoundland]], [[Nova Scotia]] and the [[Gulf of Saint Lawrence]]. This group is estimated to total about 500. The second, more easterly group is spotted from the [[Azores]] in spring to Iceland in July and August; it is presumed that the whales follow the [[Mid-Atlantic Ridge]] between the two volcanic islands. Beyond Iceland, blue whales have been spotted as far north as [[Spitsbergen]] and [[Jan Mayen]], though such sightings are rare. Scientists do not know where these whales spend their winters. The total North Atlantic population is estimated to be between 600 and 1,500.
In the Southern Hemisphere, there appear to be two distinct subspecies, ''B. m. intermedia'', the Antarctic blue whale, and the little-studied pygmy blue whale, ''B. m. brevicauda'', found in Indian Ocean waters. The most recent surveys (midpoint 1998) provided an estimate of 2,280 blue whales in the Antarctic.<ref>{{cite journal
|last=Branch
|first=T.A.
|title=Abundance of Antarctic blue whales south of 60°S from three complete circumpolar sets of surveys
|journal=Journal of Cetacean Research and Management
|volume=9
|issue=3
|pages=87–96
|year=2007}}</ref>, of which fewer than 1% are likely to be pygmy blue whales<ref>{{cite journal
|author=T.A. Branch
|title=Separating southern blue whale subspecies based on length frequencies of sexually mature females
|journal=Marine Mammal Science
|volume=23
|issue=4
|pages=803–833
|year=2007
|doi=10.1111/j.1748-7692.2007.00137.x
|last2=Abubaker
|first2=E. M. N.
|last3=Mkango
|first3=S.
|last4=Butterworth
|first4=D. S.}}</ref> Estimates from a 1996 survey were that 424 pygmy blue whales were in a small area south of [[Madagascar]] alone,<ref>{{cite journal
| title = The abundance of blue whales on the Madagascar Plateau, December 1996
| author = P.B. Best
| journal = Journal of Cetacean Research and Management
| volume = 5
| pages = 253–260
| year = 2003}}</ref> thus it is likely that numbers in the entire Indian Ocean are in the thousands. If this is true, the global numbers would be much higher than estimates predict.<ref name=BBC_pop/>
A fourth subspecies, ''B. m. indica'', was identified by [[Edward Blyth|Blyth]] in 1859 in the northern Indian Ocean, but difficulties in identifying distinguishing features for this subspecies led to it being used a synonym for ''B. m. brevicauda'', the pygmy blue whale. Records for Soviet catches seem to indicate that the female adult size is closer to that of the Pygmy Blue than ''B. m. musculus'', although the populations of ''B. m. indica'' and ''B. m. brevicauda'' appear to be discrete, and the breeding seasons differ by almost six months.<ref name = SHDistribution>{{cite journal
|title=Past and present distribution, densities and movements of blue whales ''Balaenoptera musculus'' in the Southern Hemisphere and northern Indian Ocean
|author=T. A. Branch, K. M. Stafford, D. M. Palacios
|journal = Mammal Review
|year=2007
| volume = 37
| pages = 116–175
|doi=10.1111/j.1365-2907.2007.00106.x}}</ref>
Migratory patterns of these subspecies are not well known. For example, pygmy blue whales have been recorded in the northern Indian Ocean ([[Oman]], [[Maldives]], [[Sri Lanka]]), where they may form a distinct resident population.<ref name= SHDistribution /> In addition, the population of blue whales occurring off [[Chile]] and [[Peru]] may also be a distinct population. Some Antarctic blue whales approach the eastern South Atlantic coast in winter, and occasionally, their vocalizations are heard off Peru, Western Australia, and in the northern Indian Ocean.<ref name= SHDistribution /> In Chile, the [[Cetacean Conservation Center]], with support from the [[Chilean Navy]], is undertaking extensive research and conservation work on a recently discovered feeding aggregation of the species off the coast of [[Chiloe Island]] in an area named "Golfo del Corcovado", where 326 blue whales were spotted in the summer of 2007.<ref>{{cite web
| title=Blue Whales in Chile: The Giants of Marine Conservation
| publisher=The Rufford Small Grants Foundation
| url=http://www.ruffordsmallgrants.org/files/2007%20Rufford%201st%20phase%20blue%20whale%20report%20Chile_CBA.pdf
|author=R. Hucke-Gaete, B. Carstens, A. Ruiz-Tagle y M. Bello
|format=PDF
| accessdate=2009-03-22}}</ref>
Efforts to calculate the blue whale population more accurately are supported by marine mammologists at [[Duke University]] who maintain the OBIS-SEAMAP (Ocean Biogeographic Information System—Spatial Ecological Analysis of Megavertebrate Populations), a collation of marine mammal sighting data from around 130 sources.<ref>The data for the blue whale, along with a species profile, may be found here [http://seamap.env.duke.edu/species/tsn/180528]</ref>
===Threats other than hunting===
[[Image:Blue Whale (Balaenoptera musculus) Mysticeti baleen whale.jpg|thumb|left|A blue whale surfaces off Santa Cruz Island in the [[Channel Islands of California|Channel Islands]], near Santa Barbara, CA]]
Due to their enormous size, power and speed, adult blue whales have virtually no natural predators. There is, however, one documented case in ''[[National Geographic Magazine]]'' of a blue whale being attacked by [[Orca]]s; although the Orcas were unable to kill the animal outright during their attack, the blue whale sustained massive wounds and probably died as a result of them shortly after the attack.<ref>{{cite journal
| author = Tarpy, C.
| title = Killer whale attack!
| journal = National Geographic
| year = 1979
| volume = 155
| issue = 4 (April)
| pages = 542–545 }}</ref>
Blue whales may be wounded, sometimes fatally, after colliding with ocean vessels as well as becoming trapped or entangled in fishing gear.<ref name="recplan98"/> The ever-increasing amount of ocean noise, including [[Marine mammals and sonar|sonar]], drowns out the vocalizations produced by whales, which may make it harder for them to communicate.<ref name="recplan98"/> Human threats to the potential recovery of blue whale populations also include accumulation of [[polychlorinated biphenyl]] (PCB) chemicals within the whale's body.<ref name="wheelock" />
With [[global warming]] causing glaciers and permafrost to melt rapidly and allowing a large amount of fresh water to flow into the oceans, there are concerns that if the amount of fresh water in the oceans reaches a critical point, there will be a disruption in the [[thermohaline circulation]].{{Citation needed|date=April 2010}} Considering the blue whale's migratory patterns are based on ocean temperature, a disruption in this circulation, which moves warm and cold water around the world, would be likely to have an effect on their migration.<ref>{{cite web
|url=http://www.bto.org/research/reports/researchrpt_complete/RR414_Climate%20change_&_migratory_species.pdf
|author=Robert A. Robinson, Jennifer A. Learmonth, Anthony M. Hutson, Colin D. Macleod, Tim H. Sparks, David I. Leech, Graham J. Pierce, Mark M. Rehfisch and Humphrey Q.P. Crick
|title=Climate Change and Migratory Species
|publisher=BTO
|month=August
| year=2005
| accessdate = 2007-07-09
|format=PDF}}</ref> The whales summer in the cool, high latitudes, where they feed in [[krill]]-abundant waters; they winter in warmer, low latitudes, where they mate and give birth.<ref>{{cite journal
| author = Hucke-Gaete, Rodrigo, Layla P. Osman, Carlos A. Moreno, Ken P. Findlay, and Don K. Ljungblad
| title = Discovery of a Blue Whale Feeding and Nursing Ground in Southern Chile
| journal = The Royal Society
| year = 2003
| pages = s170-s173
| url = http://www.pubmedcentral.nih.gov.oca.ucsc.edu/picrender.fcgi?artid=1810017&blobtype=pdf}}</ref>
The change in ocean temperature would also affect the blue whale's food supply. The warming trend and decreased salinity levels would cause a significant shift in krill ___location and abundance.<ref>{{cite journal
| author = Moline, Mark A., Herve Claustre, Thomas K. Frazer, Oscar Schofield, and Maria Vernet
| title = Alteration of the Food Web Along the Antarctic Peninsula in Response to a Regional Warming Trend
| journal = Global Change Biology
| volume = 10
| year = 2004
| pages = 1973–1980
| url = http://www.blackwell-synergy.com.oca.ucsc.edu/doi/abs/10.1111/j.1365-2486.2004.00825.x
| doi = 10.1111/j.1365-2486.2004.00825.x}}</ref>
==Museums==
[[Image:BlueWhaleSkeleton.jpg|thumb|Blue whale skeleton, outside the Long Marine Laboratory at the [[University of California, Santa Cruz]]]]
The [[Natural History Museum#Major specimens and exhibits|Natural History Museum]] in [[London]] contains a famous mounted skeleton and life-size model of a blue whale, which were both the first of their kind in the world but have since been replicated at the [[University of California, Santa Cruz]]. Similarly, the [[American Museum of Natural History]] in [[New York City]] has a full-size model in its Milstein Family Hall of Ocean Life.
The [[Aquarium of the Pacific]] in [[Long Beach, California]] features a life-size model of a mother blue whale with her calf suspended from the ceiling of its main hall.<ref>{{cite web
| title=Aquarium of the Pacific - Online Learning Center - Blue Whale
| url=http://www.aquariumofpacific.org/onlinelearningcenter/species/blue_whale/
| accessdate=2009-08-12}}</ref> The [[Beaty Biodiversity Museum]] at [[University of British Columbia]], Canada, is in the final stages of installing a housed display of a blue whale directly on the main campus boulevard.<ref>{{cite web|url=http://www.beatymuseum.ubc.ca/projblue01.html|title=The Blue Whale Project |date=2010|work=Beaty Biodiversity Museum|publisher=University of British Columbia|accessdate=2 May 2010|___location= Vancouver, BC}}</ref> A real skeleton of a blue whale at the [[Canadian Museum of Nature]] in Ottawa, Canada was also unveiled in May 2010 <ref>http://nature.ca/en/plan-your-visit/what-see-do/our-exhibitions/water-gallery</ref>
The Museum of Natural History in Gothenburg Sweden contains the only stuffed Blue Whale in the world. There you can also find the skeleton of the whale mounted beside the whale.
== Whale-watching ==
Living blue whales may be encountered on [[whale-watching]] cruises in the [[Gulf of Maine]]<ref>{{cite journal
|author= Wenzel FW, Mattila DK, Clapham PJ
|year=1988
|title=''Balaenoptera musculus'' in the Gulf of Maine
|journal= Mar. Mammal Sci.
|volume=4
|pages= 172–175
|doi=10.1111/j.1748-7692.1988.tb00198.x}}</ref> and are the main attractions along the north shore of the [[Gulf of Saint Lawrence]] and in the Saint Lawrence estuary.<ref name="recplan98">{{Cite book
| author = Reeves RR, Clapham PJ, Brownell RL, Silber GK
| title =Recovery plan for the blue whale ''(Balaenoptera musculus)''
| year = 1998
| page = 42
| place = Silver Spring, MD
| publisher = National Marine Fisheries Service
| accessdate=2007-06-20
| url=http://www.nmfs.noaa.gov/pr/pdfs/recovery/whale_blue.pdf
|format=PDF}}</ref>
{{Clear}}
==Footnotes==
{{Reflist|colwidth=30em}}
==References==
{{Portal|Cetaceans}}
{{Refbegin}}
*{{RefAudubonMarineMammals}} pp. 89–93.
*{{Cite book
| title = Blue Whales
| author = J. Calambokidis and G. Steiger
| year = 1998
| publisher = Voyageur Press
| isbn = 0-89658-338-4}}
*{{Cite web
| title=Blue Whale
| work= [[American Cetacean Society]]
| url= http://www.acsonline.org/factpack/bluewhl.htm
| accessdate = 2005-01-07}}
*{{Cite web
| title=Blue whale, ''Balaenoptera musculus''
| work = MarineBio.org
| url = http://marinebio.org/species.asp?id=41
| accessdate = 2006-04-21}}
* [http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/bluewhale.htm NOAA Fisheries, Office of Protected Resources] Blue whale biology & status
{{Refend}}
==External links==
{{Commons
|Balaenoptera musculus}}
{{Wikispecies
|Balaenoptera musculus}}
{{Spoken Wikipedia|Blue whale.ogg|2006-04-13}}
*[http://www.arkive.org/species/GES/mammals/Balaenoptera_musculus/ Photographs and movies from ARKive]
*[http://www.whalingmuseum.org/exhibits/kobo.html Photographs from the] [[New Bedford Whaling Museum]] *[http://www.whalingmuseum.org/exhibits/kobo.html of "Kobo", a blue whale skeleton]<!--- Note the double-linking in the line above is a deliberate to keep the section looking neat -->
*[http://www.birds.cornell.edu/brp/listen-to-project-sounds/blue-whale Blue whale vocalizations] - [[Cornell]] Lab of Ornithology—Bioacoustics Research Program
*[http://www.cetace.info/videos/Baleine_bleue/videos_baleine_bleue.php Blue whale movies, text in French]
*[http://www.panda.org/what_we_do/endangered_species/endangered_species_list/cetaceans/about/blue_whale/ World Wide Fund for Nature (WWF) - species profile for the blue whale]
*[http://news.bbc.co.uk/2/hi/science_and_environment/10340277.stm BBC News - Great whales]
*[http://www.bbc.co.uk/nature/species/Blue_Whale Blue Whale video clips and news from the BBC - BBC Wildlife Finder]
*[http://www.balaenopteramusculus.com/ Balaenoptera Musculus]
== Note ==
| |||