Editing Blue whale

{{Short description|Baleen whale, largest animal ever known}}
{{Other uses}}
{{Pp|small=yes}}
{{Pp-move}}
{{Featured article}}
{{Use American English|date=February 2022}}
{{Use dmy dates|date=February 2025}}
{{Speciesbox
| fossil_range = [[Calabrian (stage)|Early Pleistocene]] – Recent {{fossil range|1.5|0}}
| status = EN
| status_system = IUCN3.1
| status_ref =<ref name="iucn">{{cite iucn |author=Cooke, J.G. |year=2018 |errata=2019 |title=''Balaenoptera musculus'' |volume=2018 |page=e.T2477A156923585 |doi=10.2305/IUCN.UK.2018-2.RLTS.T2477A156923585.en |access-date=13 June 2024}}</ref>
| status2 = CITES_A1 
| status2_system = CITES 
| status2_ref = <ref>{{cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=14 January 2022|website=cites.org}}</ref>
| image = Anim1754 - Flickr - NOAA Photo Library.jpg
| image_caption = {{longitem|Adult blue whale <br />(''Balaenoptera musculus'')}}
| image2 = blue whale size.svg
| image2_caption = {{longitem|Size compared to an average human}}
| genus = Balaenoptera
| species = musculus
| authority = ([[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]])
| subdivision_ranks = Subspecies
| subdivision =
* ''[[Pygmy blue whale|B. m. brevicauda]]'' <small>Ichihara, 1966</small>
* ?''B. m. indica'' <small>Blyth, 1859</small>
* ''B. m. intermedia'' <small>Burmeister, 1871</small>
* ''B. m. musculus'' <small>Linnaeus, 1758</small>
| range_map = Cypron-Range Balaenoptera musculus.svg
| range_map_caption = Blue whale range (in blue)
| synonyms =
* ''Balaena musculus'' {{small|Linnaeus, 1758}}
* ''Balaenoptera gibbar'' <small>[[William Scoresby|Scoresby]] 1820</small>
* ''Pterobalaena gigas'' <small>[[Pierre-Joseph van Beneden|Van Beneden]] 1861</small>
* ''Physalus latirostris'' <small>[[William Henry Flower|Flower]] 1864</small>
* ''Sibbaldius borealis'' <small>[[John Edward Gray|Gray]] 1866</small>
* ''Flowerius gigas'' <small>[[Wilhelm Lilljeborg|Lilljeborg]] 1867</small>
* ''Sibbaldius sulfureus'' <small>[[Edward Drinker Cope|Cope]] 1869</small>
* ''Balaenoptera sibbaldii'' <small>[[Georg Ossian Sars|Sars]] 1875</small>
}}

The '''blue whale''' ('''''Balaenoptera musculus''''') is a [[marine mammal]] and a [[baleen whale]]. Reaching a maximum confirmed length of {{cvt|29.9|m}} and weighing up to {{cvt|199|t|sp=}}, it is the [[Largest and heaviest animals|largest animal known ever to have existed]].{{efn|The extinct whale species ''[[Perucetus]] colossus'' (described in 2023) has been suggested as a potential contender of the blue whale in size,<ref name="AT23">{{cite journal|last1=Bianucci|first1=G.|last2=Lambert|first2=O.|last3=Urbina|first3=M.|last4=Merella|first4=M.|last5=Collareta|first5=A.|last6=Bennion|first6=R.|last7=Salas-Gismondi|first7=R.|last8=Benites-Palomino|first8=A.|last9=Post|first9=K.|last10=de Muizon|first10=C.|last11=Bosio|first11=G.|last12=Di Celma|first12=C.|last13=Malinverno|first13=E.|last14=Pierantoni|first14=P.P.|last15=Villa|first15=I.M.|last16=Amson|first16=E.| year=2023|title=A heavyweight early whale pushes the boundaries of vertebrate morphology|journal=Nature|volume=620 |issue=7975 |pages=824–829 |doi=10.1038/s41586-023-06381-1|pmid=37532931 |bibcode=2023Natur.620..824B |s2cid=260433513 |hdl=10281/434998|hdl-access=free}}</ref> however, this was later disputed in 2024.<ref name=MP24/> Several extinct dinosaurs may also have reached a similar mass to the blue whale.<ref name="Bruhathkayosaurus2023"/>}} 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 feeder]]s; 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 [[whale vocalization|vocalize]], with a [[fundamental frequency]] ranging from 8 to 25&nbsp;Hz; their vocalizations may vary by region, season, behavior, and time of day. [[Orca]]s are their only natural predators.

The blue whale was [[Cosmopolitan species|abundant in nearly all the Earth's oceans]] until the end of the 19th&nbsp;century. It was hunted almost to the point of extinction by [[whaling|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 species (IUCN status)|Endangered]] as of 2018. It continues to face numerous man-made threats such as [[Environmental effects of shipping#Wildlife collisions|ship strikes]], [[marine pollution|pollution]], [[Noise pollution#Marine life|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 ==
{{See also|Evolution of cetaceans}}

=== 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>{{cite book | last=Linnaeus | first=Carl | date=1758 | title=Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis | location=Stockholm, Holmia | publisher=Laurentius Salvius | page=824 | author-link=Carl Linnaeus}}</ref> One of the first published descriptions of a blue whale comes from [[Robert Sibbald]]'s ''Phalainologia Nova'',<ref name=Sibbald_1692>{{cite journal | author1=Sibbald, Robert | title=Phalainologia Nova | journal=Blue Whale ("Balaenoptera Musculus") | pages=675–678 | date=1692 | author-link=Robert Sibbald}}</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>{{cite book|author1=Bortolotti, D.|title=Wild Blue: A Natural History of the World's Largest Animal | publisher=[[St. Martin's Press]]|location=New York|date=2008}}</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">{{Cite journal |last=Bennett |first=A G |date=1920 |title=On the occurrence of diatoms on the skin of whales |url=https://royalsocietypublishing.org/doi/10.1098/rspb.1920.0021 |journal=Proc. R. Soc. Lond. B |volume=91 |issue=641 |pages=352–357|doi=10.1098/rspb.1920.0021 }}</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===
{{cladogram |align=right
|caption=<small>A [[phylogenetic tree]] of six baleen whale species<ref name=Arnason_etal_2018/></small>
|clades={{clade|style=font-size:75%;line-height:75%;width:350px;
|label1=[[Balaenopteridae]]
|1={{clade
   |1=[[Minke whale]]
   |2={{clade
      |1={{clade
         |1='''''B. musculus''''' ('''blue whale''')
         |2=''B. borealis'' ([[sei whale]])
       }}
      |2={{clade 
         |1=''Eschrichtius robustus'' ([[gray whale]])
         |2={{clade
            |1=''B. physalus'' ([[fin whale]])
            |2=''Megaptera novaeangliae'' ([[humpback whale]])
          }}
       }}
    }}
 }}
}}
}}
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&nbsp;million years ago during the late [[Miocene]].<ref name=Arnason_etal_2018>{{cite journal | author1=Árnason, U. | author2=Lammers, F. | author3=Kumar, V. | author4=Nilsson, M. A. | author5=Janke, A. | title=Whole-genome sequencing of the blue whale and other rorquals finds signatures for introgressive gene flow | journal=[[Science Advances]] | volume=4 | issue = 4 | pages=eaap9873 | date=2018| bibcode=2018SciA....4.9873A | doi=10.1126/sciadv.aap9873 | pmid=29632892 | pmc=5884691}}</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&nbsp;million years ago.<ref name=Bianucci_etal_2019>{{cite journal | author1=Bianucci, G. | author2=Marx, F. G. | author3=Collareta, A. | author4=Di Stefano, A. | author5=Landini, W. | author6=Morigi, C. | author7=Varola, A. | title=Rise of the titans: baleen whales became giants earlier than thought | journal=[[Biology Letters]] | volume=15 | issue = 5 | page=20190175 | date=2019| doi=10.1098/rsbl.2019.0175 | pmid=31039728 | pmc=6548731}}</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>{{cite journal | author1=Attard, C. R. M. | author2=Beheregaray, L. B. | author3=Jenner, K. C. S. | author4=Gill, P. C. | author5=Jenner, M.-N. M. | author6=Morrice, M. G. | author7=Teske, P. R. | author8=Moller, L. M. | title=Low genetic diversity in pygmy blue whales is due to climate-induced diversification rather than anthropogenic impacts | journal=Biology Letters | volume=11 | issue=5 | page=20141037 | date=2015| doi=10.1098/rsbl.2014.1037 | pmid=25948571 | pmc=4455730}}</ref> and New Zealand blue whales have an even lower genetic diversity.<ref name=Barlow_etal_2018>{{cite journal | author1=Barlow, D. R. | author2=Torres, L. G. | author3=Hodge, K. B. | author4=Steel, D. | author5=Baker, C. S. | author6=Chandler, T. E. | author7=Bott, N. | author8=Constantine, R. | author9=Double, M. C. | author10=Gill, P. | author11=Glasgow, D. | author12=Hamner, R. M. | author13=Lilley, C. | author14=Ogle, M. | author15=Olson, P. A. | title=Documentation of a New Zealand blue whale population based on multiple lines of evidence | journal=Endangered Species Research | volume=36 | pages=27–40 | date=2018| doi=10.3354/esr00891 | doi-access=free}}</ref>

[[Whole genome sequencing]] suggests that blue whales are most closely related to [[sei whale]]s 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 whale]]s.<ref>This may have already been known to Icelanders in the 17th century, see {{cite book |last=Lindquist |first=Ole |date=1997 |title=Peasant fisherman whaling in the Northeast Atlantic area, ca 900-1900 AD |url=https://www.fishernet.is/images/stories/peasant_fisherman_whaling.pdf |location=Akureyri |publisher=Háskólinn á Akureyri |page=27 |isbn=9979-834-10-2 |access-date=2025-04-16}}</ref> The earliest description of a possible hybrid between a blue whale and a fin whale was a {{cvt|20|m}} anomalous female whale with the features of both the blue and the fin whales taken in the North Pacific.<ref name=Doroshenko_1970>{{cite journal | author1=Doroshenko, V. N. | title=A whale with features of the fin and the blue whale | journal=Izvestia TINRO | volume=70 | pages=255–257 | date=1970}}</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>{{cite journal | author1=Bérubé, M. | author2=Aguilar, A. | title=A new hybrid between a blue whale, ''Balaenoptera Musculus'', and a fin whale, "B. Physalus:" frequency and implications of hybridization | journal=Marine Mammal Science | volume=14 | issue=1 | pages=82–98 | date=1998| doi=10.1111/j.1748-7692.1998.tb00692.x| bibcode=1998MMamS..14...82B }}</ref>

Two live blue-fin whale [[Hybrid (biology)|hybrids]] have since been documented in the Gulf of St. Lawrence (Canada), and in the Azores (Portugal).<ref name=Berube_etal_2017>{{cite conference | author1=Berube, M. | author2=Oosting, T. | author3=Aguilar, A. | author4=Berrow, S. | author5=Hao, W. | author6=Heide-Jørgensen, M. P. | author7=Kovacs, K. M. | author8=Landry, S. | author9=Lydersen, C. | author10=Martin, V. | author11=Øien, N. | author12=Panigada, S. | author13=Prieto, R. | author14=Ramp, C. | author15=Robbins, J. | title=Are the "Bastards" coming back? Molecular identification of live blue and fin whale hybrids in the North Atlantic ocean | conference=22nd Biennial Conference on the Biology of Marine Mammals | location=Halifax, Nova Scotia, Canada | date=2017}}</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>{{cite web |last=Kilvert|first=Nick|url=https://www.abc.net.au/news/science/2018-07-20/dna-shows-blue-whale-hybrid-iceland-institute-says/10017276 | title=DNA test shows slaughtered blue whale is a hybrid, Iceland marine institute says | date=20 July 2018 | publisher=[[Australian Broadcasting Corporation|ABC]] | access-date=21 December 2019}}</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>{{cite web |last=Fishman|first=Margie|url=https://awionline.org/press-releases/hybrid-blue-fin-whale-still-protected | title=Hybrid blue-fin whale is still protected | date=19 July 2018 | publisher=[[Animal Welfare Institute]] | access-date=21 December 2019}}</ref> Blue-fin hybrids have been detected from genetic analysis of whale meat samples taken from Japanese markets.<ref name=Palumbi_Cipriano_1998>{{cite journal | author1=Palumbi, S. R. | author2=Cipriano, F. | title=Species identification using genetic tools: the value of nuclear and mitochondrial gene sequences in whale conservation | journal=Journal of Heredity | volume=89 | issue=5 | pages=459–464 | date=1998| doi=10.1093/jhered/89.5.459 | pmid=9768497 | doi-access=free}}</ref> Blue-fin whale hybrids are capable of being fertile. Molecular tests on a {{cvt|70|ft|order=flip}} 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>{{cite journal | author1=Spilliaert, R. | author2=Vikingsson, G. | author3=Arnason, U. | author4=Palsdottir, A. | author5=Sigurjonsson, J. | author6=Arnason, A. | title=Species hybridization between a female blue whale (''Balaenoptera rnusctllus'') and a male fin whale ("B.pbysalus"): Molecular and morphological documentation | journal=[[Journal of Heredity]] | volume=82 | issue=4 | pages=269–274 | date=1991| doi=10.1093/oxfordjournals.jhered.a111085 | pmid=1679066}}</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>{{cite journal | author1=Jossey, Sushma | author2=Haddrath, O. | author3=Loureiro, L. | author4=Weir, J. | author5=Lim, B. | author6=Miller, J. | author7=Scherer, S. | author8=Goskøyr, A | author9=Lille-Langøy, R | author10=Kovacs, Kit | author11=Lyndersen, C | author12=Routti, H | author13=Engstrom, M | title=Population structure and history of North Atlantic Blue whales (''Balaenoptera musculus musculus'') inferred from whole genome sequence analysis | journal=[[Conservation Genetics]] | volume=Open access | date=6 January 2024 | issue=2 | pages=357–371 | doi=10.1007/s10592-023-01584-5| doi-access=free | bibcode=2024ConG...25..357J | hdl=11250/3164708 | hdl-access=free }}</ref>

There is a reference to a humpback–blue whale hybrid in the [[South Pacific Ocean|South Pacific]], attributed to marine biologist Michael Poole.<ref name=Reeves_etal_2002/><ref name=Hatch_etal_2006>{{cite journal | author1=Hatch, L. T. | author2=Dopman, E. B. | author3=Harrison, R. G. | title=Phylogenetic relationships among the baleen whales based on maternally and paternally inherited characters | journal=[[Molecular Phylogenetics and Evolution]] | volume=41 | issue=1 | pages=12–27 | date=2006| doi=10.1016/j.ympev.2006.05.023 | pmid=16843014| bibcode=2006MolPE..41...12H }}</ref><ref>{{cite web |title=Genomic analyses reveal an absence of contemporary introgressive admixture between fin whales and blue whales, despite known hybrids|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0222004|date=25 September 2019|access-date=15 February 2025}}</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>{{cite report|first1=Chris W. |last1= Oliver|date=November 2020|title= Recovery Plan for the Blue Whale (''Balaenoptera musculus'') |publisher=National Oceanic and Atmospheric Administration |url=https://www.fisheries.noaa.gov/resource/document/recovery-plan-blue-whale-balaenoptera-musculus-0|access-date=12 April 2022}}</ref><ref name=SMM_2016>{{cite web|url=https://www.marinemammalscience.org/species-information/list-marine-mammal-species-subspecies/ |title=List of Marine Mammal Species and Subspecies |date=13 November 2016 | publisher=[[The Society for Marine Mammalogy]] |access-date=30 December 2019}}</ref> They have a worldwide distribution, but are mostly absent from the [[Arctic Ocean]] and the [[Mediterranean]], [[Sea of Okhotsk|Okhotsk]], and [[Bering Sea]].<ref name=NOAA/>
[[File:Blue Whale 001 body bw.jpg|thumb|right|alt=Aerial photograph of an adult blue whale showing its length |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 Current|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 Thermal Dome|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 Island]]s 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 [[Chile]]an coast might be a separate subspecies based on their geographic separation, genetics, and unique song types.<ref name=LeDuc_etal_2007>{{cite journal | author1=LeDuc, R. G. | author2=Dizon, A. E. | author3=Goto, M. | author4=Pastene, L. A. | author5=Kato, H. | author6=Nishiwaki, S. | author7=LeDuc, C. A. | author8=Brownell, R. L. | title=Patterns of genetic variation in Southern Hemisphere blue whales, and the use of assignment test to detect mixing on the feeding grounds | journal=Journal of Cetacean Research and Management | volume=9 | pages=73–80 | date=2023| doi=10.47536/jcrm.v9i1.694 | s2cid=257136658 | doi-access=free }}</ref><ref name=Torres-Florez_etal_2015>{{cite journal | author1=Torres-Florez, J. P. | author2=Olson, P. A. | author3=Bedrinana-Romano, L. | author4=Rosenbaum, H. | author5=Ruiz, J. | author6=Leduc, R. | author7=Huck-Gaete, R. | title=First documented migratory destination for eastern South Pacific blue whales | journal=Marine Mammal Science | volume=31 | issue=4 | pages=1580–1586 | date=2015| doi=10.1111/mms.12239 | doi-access=free | bibcode=2015MMamS..31.1580T }}</ref><ref name=Buchan_etal_2010>{{cite journal | author1=Buchan, S. J. | author2=Rendell, L. E. | author3=Hucke-Gaete, R. | title=Preliminary recordings of blue whale (''Balaenoptera musculus'') vocalizations in the Gulf of Corcovado, northern Patagonia Chile | journal=Marine Mammal Science | volume=26 | issue=2 | pages=451–459 | date=2010| doi=10.1111/j.1748-7692.2009.00338.x | bibcode=2010MMamS..26..451B }}</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>{{cite journal | author1=LeDuc, R. G. | author2=Archer, E. I. | author3=Lang, A. R. | author4=Martien, K. K. | author5=Hancock-Hanser, B. | author6=Torres-Florez, J. P. | author7=Hucke-Gaete, R. | author8=Rosenbaum, H. R. | author9=Van Waerebeek, K. | author10=Brownell, R. L. Jr. | author11=Taylor, B. L. | title=Genetic variation in blue whales in the eastern Pacific: implication for taxonomy and use of common wintering grounds | journal=[[Molecular Ecology]] | volume=26 | issue=3 | pages=740–751 | date=2016| doi=10.1111/mec.13940 | pmid=27891694 | s2cid=206184206 }}</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 [[Whaling in Chile|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>{{Cite journal |last1=Pastene |first1=Luis A. |last2=Acevedo |first2=Jorge |last3=Branch |first3=Trevor A. |date=2019 |title=Morphometric analysis of Chilean blue whales and implications for their taxonomy |url=https://onlinelibrary.wiley.com/doi/10.1111/mms.12625 |journal=Marine Mammal Science |language=en |volume=36 |issue=1 |pages=116–135 |doi=10.1111/mms.12625 |issn=0824-0469}}</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>{{cite journal|author1=Attard, C. R. M.|author2=Sandoval-Castillo, J|author3=Lang, A. R.|author4=Vernazzani, B. G.|author5=Torres, L. G.|author6=Baldwin, R|author7=Jenner, K. C. S.|author8=Gill, P. C.|author9=Burton, C. L. K.|author10=Barceló, A|author11=Sironi, M|author12=Jenner, M.-N. M.|author13=Morrice, M. G.|author14=Beheregaray, L. B.|author15=Möller, L. M.|year=2024|title=Global conservation genomics of blue whales calls into question subspecies taxonomy and refines knowledge of population structure|journal=Animal Conservation|volume=27|issue=5|pages=626–638|doi=10.1111/acv.12935|bibcode=2024AnCon..27..626A |doi-access=free}}</ref>

==Description==
[[File:Bluewhale2 noaa.jpg|thumb|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 [[flipper (anatomy)|flippers]]; a small {{convert|13|in|cm|order=flip|sp=us}} sickle-shaped dorsal fin located close to the tail, and a large tail stock at the root of the wide and thin [[fluke (tail)|fluke]]s. 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">{{cite book | last1=Reeves | first1=R. R. | last2=Stewart | first2=P. J. | last3=Clapham | first3=J. | last4=Powell | first4=J. A. | title=Whales, dolphins, and porpoises of the eastern North Pacific and adjacent Arctic waters: A guide to their identification | location=New York | publisher=[[Knopf]] | pages=234–237 | date=2002}}</ref><ref name="Calamb_Steig_1997" /><ref name="Sears_Perr_2009" /><ref name="Leatherwood_etal_1976" /><ref name="Leatherwood_etal_1982">{{cite journal | author1=Leatherwood, S. | author2=Reeves, R. R. | author3=Perrin, W. F. | author4=Evans, W. E. | title=Whales, dolphins, and porpoises of the eastern North Pacific and adjacent Arctic waters: A guide to their identification | journal=NOAA Technical Report NMFS Circular | volume=444 | page=245 | date=1982 | url=https://repository.library.noaa.gov/view/noaa/5472}}</ref> It has two [[blowhole (anatomy)|blowholes]] that can squirt {{convert|30|–|40|ft|order=flip|sp=us}} 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>{{cite book | last1=Calambokidis | first1=J. | last2=Steiger | first2=G. H. | title=Blue Whales | location=McGregor, MN | publisher=Voyager Press | page=72 | date=1997}}</ref><ref name=Sears_Perr_2009>{{cite book | author1=Sears, R. | author2=Perrin, W. F. | title=Encyclopedia of marine mammals | location=San Diego, CA | publisher=[[Academic Press]] | pages=120–124 | chapter=Blue whale (''Balaenoptera musculus'') | editor1-last=Perrin | editor1-first=W. F. | editor2-last=Würsig | editor2-first=B. | editor3-last=Thewissen | editor3-first=J. G. M. | date=2009}}</ref><ref name="Leatherwood_etal_1976">{{cite journal|author1=Leatherwood, S.|author2=Caldwell, D. K.|author3=Winn, H. E.|date=1976|title=Whales, dolphins, and porpoises of the western North Atlantic|url=http://aquaticcommons.org/1417/|journal=NOAA Technical Report NMFS Circular|volume=396|page=176|access-date=31 December 2019|archive-date=20 July 2020|archive-url=https://web.archive.org/web/20200720121225/http://aquaticcommons.org/1417/|url-status=dead}}</ref> The mottling patterns near the [[dorsal fin]] vary between individuals.<ref name="Sears_etal_1990">{{cite journal | author1=Sears, R. | author2=Williamson, J. M. | author3=Wenzel, F. W. | author4=Bérubé, M. | author5=Gendron, D. | author6=Jones, P. | title=Photographic identification of the blue whale (''Balaenoptera musculus'') in the Gulf of St. Lawrence, Canada | journal=[[Reports of the International Whaling Commission]] | volume=12 | pages=335–342 | date=1990}}</ref><ref name="Calambokidis_etal_2009">{{cite journal | author1=Calambokidis, J. | author2=Barlow, J. | author3=Ford, J. K. B. | author4=Chandler, T. E. | author5=Douglas, A. B. | title=Insights into the population structure of blue whales in the Eastern North Pacific from recent sightings and photographic identification | journal=[[Marine Mammal Science]] | volume=25 | issue=4 | pages=816–832 | date=2009| doi=10.1111/j.1748-7692.2009.00298.x | bibcode=2009MMamS..25..816C | s2cid=83527877 | url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1246&context=usdeptcommercepub }}</ref><ref name="Gendron_2012">{{cite journal | author1=Gendron, D. | author2=De La Cruz, U. | author3=Winn, H. E. | title=A new classification method to simplify blue whale photo-identification technique | journal=Journal of Cetacean Research and Management | volume=13 | issue=1 | pages=79–84 | date=2012}}</ref> The underbelly has lighter pigmentation and can appear yellowish due to [[diatom]]s 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">{{cite book | last1=Melville | first1=H.|author-link=Herman Melville | title=[[Moby-Dick]] | location=New York | publisher=[[Harper (publisher)|Harper & Brothers]] | page=398 | date=1851}}</ref><ref name="Scammon_1874">{{cite book | last1=Scammon | first1=C. M. | title=The Marine Mammals of the Northwestern Coast of North America | location=New York | publisher=Dover | date=1874}}</ref> The male blue whale has the [[Blue whale penis|largest penis]] in the animal kingdom, at around {{convert|3|m|ft|abbr=on}} long and {{convert|12|in|cm|abbr=on}} wide.<ref name = "bioweb">{{cite web|url=http://bioweb.uwlax.edu/bio203/s2012/olson_rile/reproduction.htm|title=Reproduction|publisher=[[University of Wisconsin]]|access-date=3 October 2012|archive-date=30 July 2012|archive-url=https://web.archive.org/web/20120730002050/http://bioweb.uwlax.edu/bio203/s2012/olson_rile/reproduction.htm|url-status=dead}}</ref>

=== Size ===
[[File:Joey williams with a 19&nbsp;foot long blue whale skull.jpg|thumb|upright|right|alt=Photograph of a blue whale skull |A blue whale [[skull]] measuring {{convert|19|ft|m|order=flip|sp=us}}]]
The blue whale is the largest animal known ever to have existed.<ref name="Ruud_1956">{{cite journal|author1=Ruud, J. T.|date=1956|title=The blue whale|journal=[[Scientific American]]|volume=195|issue=6|pages=46–50|doi=10.1038/scientificamerican1256-46|bibcode=1956SciAm.195f..46R}}</ref><ref name="Lockyer_1981">{{cite journal|author1=Lockyer, C.|date=1981|title=Growth and energy budgets of large baleen whales from the southern hemisphere|journal=FAO Fisheries Series (5) Mammals in the Seas|volume=3|pages=379–487}}</ref><ref name="Mizroch_1984">{{cite journal|author1=Mizroch, S. A.|author2=Rice, D. W.|author3=Breiwick, J. M.|date=1984|title=The blue whale, ''Balaenoptera musculus''|journal=Marine Fisheries Review|volume=46|pages=15–19}}</ref> Some studies have estimated that certain [[Shastasauridae|shastasaurid]] [[ichthyosaur]]s and the ancient whale ''[[Perucetus]]'' could have rivalled the blue whale in size, with ''Perucetus'' actually being heavier with a mean weight of {{cvt|180|t}}.<ref name="AT23" /><ref name="PLOS One2018">{{cite journal |last1=De la Salle |first1=Paul |last2=R. Lomax |first2=Dean |last3=A. Massare |first3=Judy |last4=Gallois |first4=Ramues |name-list-style=vanc |year=2018 |title=A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff 'dinosaurian' bones |url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194742 |journal=PLOS ONE |volume=13 |issue=4 |doi=10.6084/m9.figshare.5975440}}</ref> However, these estimates were based on fragmentary remains, and the proposed size for ''Perucetus'' was disputed by studies in 2024.<ref name=MP24>{{Cite journal|last1=Motani |first1=R. |last2=Pyenson |first2=N. D. |year=2024 |title=Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale ''Perucetus colossus'' |journal=PeerJ |volume=12 |at=e16978 |doi=10.7717/peerj.16978 |doi-access=free |pmid=38436015 |pmc=10909350 }}</ref> Other studies estimate that, on land, large [[Sauropoda|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">{{Cite journal |last1=Paul |first1=Gregory S. |last2=Larramendi |first2=Asier |date=11 April 2023 |title=Body mass estimate of ''Bruhathkayosaurus'' and other fragmentary sauropod remains suggest the largest land animals were about as big as the greatest whales |journal=Lethaia |language=en |volume=56 |issue=2 |pages=1–11 |doi=10.18261/let.56.2.5 |bibcode=2023Letha..56..2.5P |s2cid=259782734 |issn=0024-1164|doi-access=free }}</ref>

The [[International Whaling Commission]] (IWC) whaling database reports 88 individuals longer than {{convert|30|m|sp=us}}, including one of {{convert|33|m|sp=us}}.<ref name="McClain_2015">{{cite journal | author1=McClain, C. R. | author2=Balk, M. A. | author3=Benfield, M. C. | author4=Branch, T. A. | author5=Chen, C. | author6=Cosgrove, J. | author7=Dove, A. D. M. | author8=Helm, R. R. | author9=Hochberg, F. G. | author10=Gaskins, L. C. | author11=Lee, F. B. | author12=Marshall, A. | author13=McMurray, S. E. | author14=Schanche, C. | author15=Stone, S. N. | title=Sizing ocean giants: patterns of intraspecific size variation in marine megafauna | journal=[[PeerJ]] | volume=e715 | page=e715 | date=2015 | doi=10.7717/peerj.715| pmid=25649000 | pmc=4304853 | doi-access=free }}</ref> The [[Discovery Committee]] reported lengths up to {{convert|102|ft|order=flip|sp=us}}.<ref name=Mackintosh_1942>{{cite journal | author1=Mackintosh, N. A. | title=The southern stocks of whalebone whales | journal=[[Discovery Reports]] | volume=22 | issue=3889 | pages=569–570 | date=1942| url=https://archive.org/details/cbarchive_120108_thesouthernstocksofwhalebonewh1943/page/n9/mode/2up| bibcode=1944Natur.153..569F | doi=10.1038/153569a0 | s2cid=41590649 }}</ref> The longest scientifically measured individual blue whale was {{convert|98|ft|order=flip|sp=us}} from rostrum tip to tail notch.<ref name=Sears_Calamb_2002>{{cite book | last1=Sears | first1=R. | last2=Calambokidis | first2=J. | title=Update COSEWIC status report on the blue whale (''Balaenoptera musculus'') in Canada | location=Ottawa, ON | publisher=[[Committee on the Status of Endangered Wildlife in Canada]] | page=32 | date=2002}}</ref> Female blue whales are larger than males.<ref name=Sears_Perr_2009/><ref name=Ralls_1976>{{cite journal | author1=Ralls, K. | title=Mammals in which females are larger than males | journal=[[The Quarterly Review of Biology]] | volume=51 | issue=2 | pages=245–270 | date=1976| doi=10.1086/409310 | pmid=785524 | s2cid=25927323 }}</ref> Hydrodynamic models suggest a blue whale could not exceed {{convert|33|m|ft}} because of metabolic and energy constraints.<ref name=Potvin_2012>{{cite journal | author1=Potvin, J. | author2=Goldbogen, J. | author3=Chadwick, R. E. | title=Metabolic Expenditures of Lunge Feeding Rorquals Across Scale: Implications for the Evolution of Filter Feeding and the Limits to Maximum Body Size | journal=[[PLOS ONE]] | volume=7 | issue=9 | page=e44854 | doi=10.1371/journal.pone.0044854 | pmid=23024769 | pmc=3443106 | date=2012| bibcode=2012PLoSO...744854P | doi-access=free }}</ref>

The average length of sexually mature female blue whales is {{convert|72.1|ft|order=flip|sp=us}} for Eastern North Pacific blue whales, {{convert|79|ft|order=flip|sp=us}} for central and western North [[Pacific]] blue whales, {{convert|68–78|ft|order=flip|sp=us}} for North [[Atlantic]] blue whales, {{convert|83.4|–|86.3|ft|order=flip|sp=us}} for Antarctic blue whales, {{convert|77.1|ft|order=flip|sp=us}} for Chilean blue whales, and {{convert|69.9|ft|order=flip|sp=us}} for pygmy blue whales.<ref name="McClain_2015"/><ref name=Branch_2007a>{{cite journal | author1=Branch, T. A. | author2=Abubaker, E. M. N. | author3=Mkango, S. | author4=Butterworth, D. S. | 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 | date=2007| doi=10.1111/j.1748-7692.2007.00137.x | bibcode=2007MMamS..23..803B }}</ref><ref name=Gilpatrick_Perryman_2008>{{cite journal | author1=Gilpatrick, J. W. | author2=Perryman, W. L. | title=Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (''Balaenoptera musculus'') | journal=Journal of Cetacean Research and Management | volume=10 | issue=1 | pages=9–21 | date=2008| doi=10.47536/jcrm.v10i1.654 | s2cid=256926335 | doi-access=free }}</ref>

In the Northern Hemisphere, males weigh an average {{convert|100|t|lb|sp=us}} and females {{convert|112|t|lb|sp=us}}. Eastern North [[Pacific]] blue whale males average {{convert|88.5|t|lb|sp=}} and females {{convert|100|t|lb|sp=}}. Antarctic males average {{convert|112|t|lb|sp=}} and females {{convert|130|t|lb|sp=}}. Pygmy blue whale males average {{convert|83.5|t|lb|sp=}} to {{convert|99|t|lb|sp=}}.<ref name=Lockyer_1976>{{cite journal | author1=Lockyer, C. | title=Body weights of some species of large whales | journal=[[J. Cons. Int. Explor. Mer]] | volume=36 | issue=3 | pages=259–273 | date=1976| doi=10.1093/icesjms/36.3.259 }}</ref> The weight of the heart of a stranded North Atlantic blue whale was {{convert|180|kg|lb|abbr=on|sp=}}, the largest known in any animal.<ref>{{cite web |url=http://www.bbc.com/earth/story/20150820-see-the-worlds-biggest-heart-blue-whales-is-first-to-be-preserved?ns_mchannel=social&ns_campaign=BBC_iWonder&ns_source=twitter&ns_linkname=knowledge_and_learning |title=See the world's biggest heart |access-date=21 August 2015 |archive-date=16 September 2020 |archive-url=https://web.archive.org/web/20200916133445/http://www.bbc.com/earth/story/20150820-see-the-worlds-biggest-heart-blue-whales-is-first-to-be-preserved?ns_mchannel=social&ns_campaign=BBC_iWonder&ns_source=twitter&ns_linkname=knowledge_and_learning |url-status=dead }}</ref> The record-holder blue whale was recorded at {{convert|173|tonne|short ton|-1|lk=on|abbr=off}},<ref>{{cite web | title = Assessment and Update Status Report on the Blue Whale ''Balaenoptera musculus'' | publisher = Committee on the Status of Endangered Wildlife in Canada | year = 2002 | url = http://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_blue_whale_e.pdf | access-date = 19 April 2007}}</ref> with estimates of up to {{convert|199|tonne|short ton|-1|lk=on|abbr=off}}.<ref>{{cite journal |last1=McClain |first1=Craig R. |last2=Balk |first2=Meghan A. |last3=Benfield |first3=Mark C. |last4=Branch |first4=Trevor A. |last5=Chen |first5=Catherine |last6=Cosgrove |first6=James |last7=Dove |first7=Alistair D.M. |last8=Gaskins |first8=Leo |last9=Helm |first9=Rebecca R. |last10=Hochberg |first10=Frederick G. |last11=Lee |first11=Frank B. |last12=Marshall |first12=Andrea |last13=McMurray |first13=Steven E. |last14=Schanche |first14=Caroline |last15=Stone |first15=Shane N. |last16=Thaler |first16=Andrew D. |title=Sizing ocean giants: patterns of intraspecific size variation in marine megafauna |journal=PeerJ |date=13 January 2015 |volume=3 |pages=e715 |doi=10.7717/peerj.715 |pmid=25649000 |pmc=4304853 |doi-access=free }}</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 {{convert|25|m|ft}} long individual was estimated to weigh approximately {{convert|101|-|119|tonne|ST}}, while a {{convert|30|m|ft}} long individual was estimated to weigh approximately {{convert|184|-|205|tonne|ST}}. Considering that the largest blue whale was indeed {{convert|33|m|ft}} long, they estimated that a blue whale of such length would have weighed approximately {{convert|252|-|273|tonne|ST}}.<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&nbsp;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>{{Cite journal |last=Roston |first=Rachel A. |date=2013 |title=Anatomy and Age Estimation of an Early Blue Whale (Balaenoptera musculus) Fetus |url=https://anatomypubs.onlinelibrary.wiley.com/doi/pdf/10.1002/ar.22678 |access-date=23 November 2024 |journal=The Anatomical Record|volume=296 |issue=4 |pages=709–722 |doi=10.1002/ar.22678 |pmid=23447333 |doi-access=free }}</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>{{cite journal | author1=Purves, P. E. | title=The wax plug in the external auditory meatus of the | journal=Discovery Reports | volume=27 | pages=259–273 | date=1955}}</ref><ref name=Gabriele_etal_2010>{{cite journal | author1=Gabriele, C. M. | author2=Lockyer, C. | author3=Straley, J. M. | author4=Juasz, C. M. | author5=Kato, H. | title=Sighting history of a naturally marked humpback whale (''Megaptera novaeangliae'') suggests ear plug growth layer groups are deposited annually | journal=Marine Mammal Science | volume=26 | issue=2 | pages=443–450 | date=2010| doi=10.1111/j.1748-7692.2009.00341.x | bibcode=2010MMamS..26..443G }}</ref><ref name=Lockyer_1984a>{{cite journal | author1=Lockyer, C. | title=Age Determination by means of the ear plug in baleen whales | journal=Report of the International Whaling Commission | volume=34 | pages=692–696 | date=1984}}</ref> The oldest blue whale found was determined, using this method, to be 110 years old.<ref name=natgeo>{{cite magazine|magazine=[[National Geographic]]|title=Blue whale|url=https://www.nationalgeographic.com/animals/mammals/facts/blue-whale|archive-url=https://archive.today/20220607195937/https://www.nationalgeographic.com/animals/mammals/facts/blue-whale|archive-date=7 June 2022|access-date=3 March 2023}}</ref><ref name=wdc>{{cite web|title=Blue whale|work=[[Whale and Dolphin Conservation]]|url=https://us.whales.org/whales-dolphins/species-guide/blue-whale/|archive-url=https://archive.today/20230303051510/https://us.whales.org/whales-dolphins/species-guide/blue-whale/|archive-date=3 March 2023|access-date=3 March 2023}}</ref> The maximum age of a pygmy blue whale determined this way is 73 years.<ref name=Branch_2008>{{cite journal | author1=Branch, T. A. | title=Biological parameters for pygmy blue whales | journal=International Whaling Commission Document | volume=SC/60/SH6 | page=13 | date=2008}}</ref> In addition, female blue whales develop scars or [[corpora albicantia]] on their ovaries every time they ovulate.<ref name=Perr_Donov_1984>{{cite book | last1=Perrin | first1=W. F. | last2=Donovan | first2=G. P. | chapter=Report of the Workshop | title=Reproduction in whales, dolphin and porpoises | location=Cambridge, UK | publisher=[[International Whaling Commission]] | date=1984 | editor1-last=Perrin | editor1-first=W. F. | editor2-last=Donovan | editor2-first=G. P. | editor3-last=DeMaster | editor3-first=D. P.}}</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|right|thumb|alt=Photograph of a whale blowing |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 [[Animal migration|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>{{cite web|url=https://www.fisheries.noaa.gov/species/blue-whale#overview | title=Blue Whale | publisher=NOAA Fisheries | access-date= 11 November 2019}}</ref> The animals appear to use memory to locate the best feeding areas.<ref>{{cite journal|author1=Abrahms, B.|author2=Hazen, E. L.|author3=Aikens, E. O.|author4=Savoca, M. S.|author5=Goldbogen, J. A.|author6=Goldbogen, S. J.|author7=Jacox, M. G.|author8=Irvine, L. M.|author9=Palacios, D. M.|author10=Mate, B. R.|year=2019|title=Memory and resource tracking drive blue whale migrations|journal=Proceedings of the National Academy of Sciences|volume=116|issue=12|pages=5582–5587|doi=10.1073/pnas.1819031116| pmid=30804188 | pmc=6431148 |bibcode=2019PNAS..116.5582A | doi-access=free }}</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>{{cite journal | author1=Geijer, C. K. | author2=Notarbartolo di Sciara, G. | author3=Panigada, S. | title=Mysticete migration revisited: Are Mediterranean fin whales an anomaly? | journal=Mammal Review | volume=46 | issue=4 | pages=284–296 | date=2016| doi=10.1111/mam.12069 }}</ref> Blue whale typically swim at {{convert|2|–|8|km/h|sp=us}} but may swim faster at {{convert|32|–|36|km/h|sp=us}} during encounters with boats, predators or other individuals.<ref>{{cite web |last1=EEN|first1=BREIWICK|title=Blue Whale (Balaenoptera musculus)|page=13|url=https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_blue_whale_e.pdf|access-date=24 February 2025}}</ref> Their massive size limits their ability to [[Cetacean surfacing behaviour#Breaching and lunging|breach]].<ref>{{cite journal|author1=Segre, P. S.|author2=Potvin, J|author3=Cade, D. E.|author4=Calambokidis, J|author5=Di Clemente , J|author6=Fish, F. E.|author7=Friedlaender, A. S.|author8=Gough, W. T.|author9=Kahane-Rapport, S. R.|author10=Oliveira, C|author11=Parks, S. E.|author12=Penry, G. S.|author13=Simon, M|author14=Stimpert, A. K.|author15=Wiley, D. N.|author16=Bierlich, K. C.|author17=Madsen, P. T.|author18=Goldbogen, J. A.|year=2020|title=Energetic and physical limitations on the breaching performance of large whales|journal=Physics of Living Systems|volume=9 |doi=10.7554/eLife.51760 |pmid=32159511 |pmc=7065846 |doi-access=free }}</ref>

The greatest dive depth reported from tagged blue whales was {{convert|315|m|sp=us}}.<ref name=Goldbogen_etal_2011/> Their theoretical aerobic dive limit was estimated at 31.2 minutes,<ref name=Croll_etal_2001>{{cite journal | author1=Croll, D. A. | author2=Aceveo-Gutierrez, A. | author3=Tershy, B. R. | author4=Urban-Ramirez, J. | title=The diving behavior of blue and fin whales: Is dive duration shorter than expected based on oxygen stores? | journal= Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology| volume=129 | issue=4 | pages=797–809 | date=2010| doi=10.1016/S1095-6433(01)00348-8 | pmid=11440866 }}</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 {{convert|506|m|sp=us}}.<ref name=Owen_etal_2016>{{cite journal | author1=Owen, K. | author2=Jenner, C. S. | author3=Jenner, M.-N. M. | author4=Andrews, R. D. | title=A week in the life of a pygmy blue whale: migratory dive depth overlaps with large vessel drafts | journal=Animal Biotelemetry | volume=4 | issue=17 | pages=1–11 | date=2016 | doi=10.1186/s40317-016-0109-4| doi-access=free | bibcode=2016AnBio...4...17O }}</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>{{cite journal|author1=Goldbogen, J. A.|author2=Cade, D. E.|author3=Calambokidis, J.|author4=Czapanskiy, M. F.|author5=Fahlbusch, J.|author6=Friedlaender, A. S.|author7=Gough, W. T.|author8=Kahane-Rapport, S. R.|author9=Savoca, M. S.|author10=Ponganis, K. V.|author11=Ponganis, P. J.|year=2019|title=Extreme bradycardia and tachycardia in the world's largest animal|journal=Proceedings of the National Academy of Sciences|volume=116|issue=50|pages=25329–25332|doi=10.1073/pnas.1914273116| pmid=31767746 | pmc=6911174 |bibcode=2019PNAS..11625329G | doi-access=free }}</ref>

===Diet and feeding===
[[File:Blue-whale.jpg|thumb|alt=Photograph blue whale near surface with throat bulging | 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 {{convert|220|t|sp=us}} of water at one time.<ref name=Fossette_etal_2017>{{cite journal | author1=Fossette, S. | author2=Abrahms, B. | author3=Hazen, E. L. | author4=Bograd, S. J. | author5=Zilliacus, K. M. | author6=Calambokidis, J. | author7=Burrows, J. A. | author8=Goldbogen, J. A. | author9=Harvey, J. T. | author10=Marinovic, B. | author11=Tershy, B. | author12=Croll, D. A. | title=Resource partitioning facilitates coexistence in sympatric cetaceans in the California Current | journal=[[Ecology and Evolution]] | volume=7 | issue=1 | pages=9085–9097 | date=2017| doi=10.1002/ece3.3409 | pmid=29152200 | pmc=5677487 | bibcode=2017EcoEv...7.9085F }}</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>{{cite journal | author1=Goldbogen, J. A. | author2=Calambokidis, J. | author3=Oleson, E. | author4=Potvin, J.|author5-link=Nicholas Pyenson | author5=Pyenson, N. D. | author6=Schorr, G. | author7=Shadwick, R. E. | title=Mechanics, hydrodynamics and energetics of blue whale lunge feeding: Efficiency dependence on krill density | journal=Journal of Experimental Biology | volume=214 | issue=1 | pages=131–46 | date=2011| doi=10.1242/jeb.048157 | pmid=21147977 | doi-access=free | bibcode=2011JExpB.214..131G }}</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>{{cite journal | author1=Goldbogen, J. A. | author2=Calambokidis, J. | author3=Friedlaender, A. S. | author4=Francis, J. | author5=DeRuiter, A. L. | author6=Stimpert, A. K. | author7=Falcone, E. | author8=Southall, B. L. | title=Underwater acrobatics by the world's largest predator: 360° rolling manoeuvres by lunge-feeding blue whales | journal=[[Biology Letters]] | volume=9 | issue=1 | doi=10.1098/rsbl.2012.0986 | pmid=23193050 | pmc=3565519 | page=20120986 | date=2012}}</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>{{Cite web |last=Barlow |first=Dawn R. |date=2023 |title=Shaped by their Environment: Variation in Blue Whale Morphology Across Three Productive Coastal Ecosystems |url=https://academic.oup.com/iob/article/5/1/obad039/7438866 |access-date=23 November 2024 |website=Integrative Organismal Biology}}</ref> Blue whales have to engulf densities greater than 100 krill/m<sup>3</sup> to maintain the cost of lunge feeding.<ref name=Goldbogen_etal_2011/><ref name=Hazen_etal_2015>{{cite journal | author1=Hazen, E. L. | author2=Friedlaender, A. S. | author3=Goldbogen, J. A. | title=Blue whales ("Balaenoptera musculus") optimize foraging efficiency by balancing oxygen use and energy gain as a function of prey density | journal=Science Advances | volume=1 | issue=9 | page=e1500469 | date=2015| bibcode=2015SciA....1E0469H | doi=10.1126/sciadv.1500469 | pmid=26601290 | pmc=4646804 | doi-access=free }}</ref> They can consume {{convert|34,776|–|1,912,680|kJ|kcal|sp=us}} 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 {{convert|1,120|±|359|kg|sp=us}} of krill a day.<ref name=Brodie_1975>{{cite journal | author1=Brodie, P. F. | title=Cetacean energetics, an overview of intraspecific size variation | journal=Ecology | volume=56 | issue=1 | pages=152–161 | date=1975| doi=10.2307/1935307 | jstor=1935307 | bibcode=1975Ecol...56..152B }}</ref><ref name=Croll_etal_2006>{{cite book | author1=Croll, D. A. | author2=Kudela, R. | author3=Tershy, B. R. | title=Whales, Whaling and Ocean Ecosystems | chapter=Ecosystem impact of the decline of large whales in the North Pacific | publisher=University of California Press | location=Berkeley, CA | editor1-last=Estes | editor1-first=J. A. | pages=202–214 | date=2006}}</ref>  On average, a blue whale eats {{cvt|4|t|sp=}} 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">{{Cite journal |last1=de Vos |first1=Asha |last2=Faux |first2=Cassandra E. |last3=Marthick |first3=James |last4=Dickinson |first4=Joanne |last5=Jarman |first5=Simon N. |date=6 April 2018 |title=New Determination of Prey and Parasite Species for Northern Indian Ocean Blue Whales |journal=Frontiers in Marine Science |language=English |volume=5 |doi=10.3389/fmars.2018.00104 |doi-access=free |issn=2296-7745}}</ref> In California, they feed mostly on ''[[Thysanoessa spinifera]],'' but also less commonly on North pacific krill (''[[Euphausia pacifica]]'').<ref>{{Cite journal |last1=Fiedler |first1=Paul C. |last2=Reilly |first2=Stephen B. |last3=Hewitt |first3=Roger P. |last4=Demer |first4=David |last5=Philbrick |first5=Valerie A. |last6=Smith |first6=Susan |last7=Armstrong |first7=Wesley |last8=Croll |first8=Donald A. |last9=Tershy |first9=Bernie R. |last10=Mate |first10=Bruce R. |date=1 August 1998 |title=Blue whale habitat and prey in the California Channel Islands |url=https://www.sciencedirect.com/science/article/abs/pii/S0967064598800179 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=45 |issue=8 |pages=1781–1801 |doi=10.1016/S0967-0645(98)80017-9 |bibcode=1998DSRII..45.1781F |issn=0967-0645}}</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 [[Sergestidae|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, [[Amphipoda|amphipods]], [[cephalopod]]s, and [[Scyphozoa|scyphozoan jellyfish]] in their diet.<ref name=":1" />

Blue whales appear to avoid directly competing with other baleen whales.<ref name=Hardin_1960>{{cite journal | author1=Hardin, G. | s2cid=18542809 | title=The competitive exclusion principle | journal=Science | volume=131 | issue=3409 | pages=1292–1297 | date=1960| doi=10.1126/science.131.3409.1292 | pmid=14399717 | bibcode=1960Sci...131.1292H }}</ref><ref name=Hutchinson_1961>{{cite journal | author1=Hutchinson, G. E. | s2cid=86353285 | title=The Paradox of the Plankton | journal=[[The American Naturalist]] | volume=95 | issue=882 | pages=137–145 | date=1961| doi=10.1086/282171 | bibcode=1961ANat...95..137H }}</ref><ref name=Pianka_1974>{{cite journal | author1=Pianka, E. R. | title=Niche overlap and diffuse competition | journal=Proceedings of the National Academy of Sciences | volume=71 | issue=5 | pages=2141–2145 | date=1974| doi=10.1073/pnas.71.5.2141 | pmid=4525324 | pmc=388403 | bibcode=1974PNAS...71.2141P | doi-access=free }}</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>{{cite thesis | author1=Doniol-Valcroze, T. | title=Habitat selection and niche characteristics of rorqual whales in the northern Gulf of St. Lawrence (Canada) | type=PhD | publisher=[[McGill University]] | location=Montreal, Canada | date=2008}}</ref><ref name=Friedlaender_etal_2015>{{cite journal | author1=Friedlaender, A. S. | author2=Goldbogen, J. A. | author3=Hazen, E. L. | author4=Calambokidis, J. | author5=Southall, B. L. | title=Feeding performance by sympatric blue and fin whales exploiting a common prey resource | journal=Marine Mammal Science | volume=31 | issue=1 | pages=345–354 | date=2015| doi=10.1111/mms.12134 | bibcode=2015MMamS..31..345F }}</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>{{cite journal | author1=Santora, J. A. | author2=Reiss, C. S. | author3=Loeb, V. J. | author4=Veit, R. R. | title=Spatial association between hotspots of baleen whales and demographic patterns of Antarctic krill ''Euphausia superba'' suggests size-dependent predation | journal=Marine Ecology Progress Series | volume=405 | pages=255–269 | date=2010| doi=10.3354/meps08513 | bibcode=2010MEPS..405..255S | doi-access=free }}</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>{{Cite web |last=Melica |first=Valentina |date=2020 |title=Reproduction and Stress Response Endocrinology in Blue (Balaenoptera musculus) and Gray (Eschrichtius robust) Whales |url=https://scholarworks.alaska.edu/bitstream/handle/11122/12414/Melica_V_2020.pdf |access-date=23 November 2024 |website=Scholarworks Alaska}}</ref>

===Reproduction and birth===
[[File:BlueWhaleWithCalf.jpg|thumb|alt=Photograph of a blue whale calf and its mother | A blue whale calf with its mother]]
The age of sexual maturity for blue whales is thought to be 5–15 years.<ref>{{cite web |last1=JM|first1=BREIWICK|title=The Blue Whale,|page=17|url=https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/MFR/mfr464/mfr4644.pdf|access-date=23 February 2025}}</ref> In the Northern Hemisphere, the length at which they reach maturity is {{convert|21|–|23|m|sp=us}} for females and {{convert|20|–|21|m|sp=us}} for males. In the Southern Hemisphere, the length of maturity is {{convert|23|–|24|m|sp=us}} and {{convert|22|m|sp=us}} for females and males respectively.<ref name=Sears_Perrin_2018>{{cite book | author1=Sears, R. | author2=Perrin, W. F. | title=Encyclopedia of marine mammals | chapter=Blue Whale: "Balaenoptera musculus" | publisher=Academic Press | location=London, UK | editor1-last=Würsig | editor1-first=B. | editor2-last=Thewissen | editor2-first=J. G. M. | editor3-last=Kovacs | editor3-first=K. M. | pages=110–114 | date=2018}}</ref> Male pygmy blue whales average {{convert|61.4|ft|order=flip|sp=us}} at sexual maturity.<ref name=Ichihara_1964>{{cite journal | author1=Ichihara T. | title=The pygmy blue whale, ''Balaenoptera musculus brevicauda'', a new subspecies from Antarctic | journal=Norsk. Hvalf. Tid. | volume=6 | date=1964}}</ref><ref name=Sazhinov_1970>{{cite journal | author1=Sazhinov E. G. | title=The onset of sexual and physical maturity for pygmy blue whales (''Balaenoptera musculus brevicauda''. Ichinara. 1966) | journal=Whales of the Southern Hemisphere | issue=29 | pages=34–40 | date=1970}}</ref> Female pygmy blue whales are {{convert|68.9|–|71.2|ft|order=flip|sp=us}} 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>{{cite journal | author1=Branch, T. A. | author2=Mikhalev, Y. A. | title=Regional differences in length at sexual maturity for female blue whales based on recovered Soviet whaling data | journal=Marine Mammal Science | volume=24 | issue=3 | pages=690–703 | date=2008| doi=10.1111/j.1748-7692.2008.00214.x | bibcode=2008MMamS..24..690B }}</ref> Since corpora are added every ~2.5 years after sexual maturity, physical maturity is assumed to occur at 35 years.<ref>{{cite web |title=Sex ratios in blue whales from conception onward|page=23|url=https://repository.library.noaa.gov/view/noaa/63149/noaa_63149_DS1.pdf|access-date=7 February 2025}}</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 [[Polygyny in animals|polygynous]], with males competing for females.<ref name=Sears_Perrin_2018/><ref name=Sears_etal_2013>{{cite journal | author1=Sears, R. | author2=Ramp, C. | author3=Douglas, A. B. | author4=Calambokidis, J. | title=Reproductive parameters of eastern North Pacific blue whales ''Balaenoptera musculus'' | journal=Endangered Species Research | volume=22 | issue=1 | pages=23–31 | date=2013| doi=10.3354/esr00532 | doi-access=free }}</ref> A male blue whale typically trails a female and will fight off potential rivals.<ref name=Schall_etal_2019>{{cite journal | author1=Schall, E. | author2=Di Lorio, L. | author3=Berchok, C. | author4=Filún, D. | author5=Bedriñana-Romano, L. | author6=Buchan, S. J. | author7=Van Opzeeland, I. | author8=Sears, R. | author9=Hucke-Gaete, R. | title=Visual and passive acoustic observations of blue whale trios from two distinct populations | journal=Marine Mammal Science | volume=36 | issue=1 | doi=10.1111/mms.12643 | pages=365–374 | date=2019| doi-access=free | hdl=1912/24953 | hdl-access=free }}</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>{{cite journal | author1=Sergeant, D. E. | title=Feeding rates of Cetacea | journal=Fiskeridir. SKR. Havundersok | volume=15 | pages=246–258 | date=1969}}</ref> amounting to 60% of their overall body weight throughout summer foraging periods.<ref name=Sears_Perrin_2018/><ref name=Lockyer_1984b>{{cite journal | author1=Lockyer, C. | title=Review of baleen whale (Mysticeti) reproduction and implications for management | journal=Report of the International Whaling Commission | volume=6 | pages=27–50 | date=1984}}</ref> [[Gestation]] may last 10–12 months with calves being {{convert|6|–|7|m|sp=us}} long and weighing {{convert|2|–|3|t|sp=us}} at birth.<ref name=Sears_Perrin_2018/> Estimates suggest that because calves require {{convert|2|-|4|kg|sp=us}} milk per kg of mass gain, blue whales likely produce {{convert|220|kg|sp=us}} of milk per day (ranging from {{convert|110|to|320|kg|sp=us}} of milk per day).<ref name=Oftedal_1997>{{cite journal | author1=Oftedal, O. T. | s2cid=19588882 | title=Lactation in whales and dolphins: Evidence of divergence between baleen- and toothed-species | journal=Journal of Mammary Gland Biology and Neoplasia | volume=2 | issue=3 | pages=205–230 | date=1997| doi=10.1023/A:1026328203526 | pmid=10882306 }}</ref> The first video of a calf thought to be nursing was filmed in New Zealand in 2016.<ref>{{cite web | url=https://www.nationalgeographic.com/news/2016/03/160302-blue-whale-mother-calf-nursing-video-pygmy-new-zealand/ | archive-url=https://web.archive.org/web/20191231040656/https://www.nationalgeographic.com/news/2016/03/160302-blue-whale-mother-calf-nursing-video-pygmy-new-zealand/ | url-status=dead | archive-date=31 December 2019 | title=Exclusive Video May Show Blue Whale Calf Nursing | date=2 March 2016 | publisher=[[National Geographic]] | access-date=20 December 2019}}</ref> Calves may be [[weaned]] when they reach 6–8 months old at a length of {{convert|53|ft|order=flip|sp=us}}.<ref name=Sears_Perrin_2018/> They gain roughly {{convert|37,500|lb|sp=us}} 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>{{cite journal|last=Branch|first=T. A.|year=2025|title=Timing hypothesis explains the mystery of the missing blue whale calves|journal=Endangered Species Research|volume=56|pages=53–67|doi=10.3354/esr01383|doi-access=free}}</ref>

===Vocalizations===
{{listen
 | pos          = right
 | filename     = Blue whale atlantic1.ogg
 | title        = A blue whale song
 | description  = Recorded in the Atlantic (1)
 | format       = [[Ogg]]
 | filename2    = Blue whale atlantic3.ogg
 | title2       = A blue whale song
 | description2 = Recorded in the Atlantic (2)
 | format2      = [[Ogg]]
 | filename3    = Blue_Whale_NE_Pacific.ogg
 | title3       = A blue whale song
 | description3 = Recorded in North Eastern Pacific
 | format3      = [[Ogg]]
 | filename4    = Blue_Whale_South_Pacific.ogg
 | title4       = A blue whale song
 | description4 = Recorded in the South Pacific
 | format4      = [[Ogg]]
 | filename5    = Blue_Whale_West_Pacific.ogg
 | title5       = A blue whale song
 | description5 = Recorded in the West Pacific
 | format5      = [[Ogg]]
}}
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|low-frequency]] sounds.<ref name=Yamato_etal_2008>{{cite journal | author1=Yamato, M. | author2=Ketten, D. R. | author3=Arruda, J. | author4=Cramer, S. | title=Biomechanical and structural modeling of hearing in baleen whales | journal=Bioacoustics | volume=17 | issue=1–3 | pages=100–102 | date=2008| doi=10.1080/09524622.2008.9753781 | bibcode=2008Bioac..17..100Y | s2cid=85314872 }}</ref> The [[fundamental frequency]] for blue whale [[Animal communication#Auditory|vocalizations]] ranges from 8 to 25&nbsp;Hz.<ref name=Stafford_etal_1998>{{cite journal | author1=Stafford, K. M. | author2=Fox, G. C. | author3=Clark, D. S. | title=Long-range acoustic detection and localization of blue whale calls in the northeast Pacific Ocean | journal=Journal of the Acoustical Society of America | volume=50 | issue=4 | pages=1193–1198 | date=1998| bibcode=1998ASAJ..104.3616S | doi=10.1121/1.423944 | pmid=9857519 }}</ref> Blue whale songs vary between populations.<ref name=McDonald_etal_2006>{{cite journal | author1=McDonald, M. A. | author2=Mesnick, S. L. | author3=Hildebrand, J. A. | title=Biogeographic characterization of blue whale song worldwide: Using song to identify populations | journal=Journal of Cetacean Research and Management | volume=8 | pages=55–66 | date=2023| doi=10.47536/jcrm.v8i1.702 | s2cid=18769917 | doi-access=free }}</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>{{cite book | author1=Aroyan, J. L. | author2=McDonald, M. A. | author3=Webb, S. C. | author4=Hildebrand, J. A. | author5=Clark, D. S. | author6=Laitman, J. T. | author7=Reidenberg, J. S. | title=Hearing by whales and dolphins | chapter=Acoustic models of sound production and propagation | editor1-last=Au | editor1-first=W. W. A. | editor2-last=Popper | editor2-first=A. | editor3-last=Fay | editor3-first=R. N. | publisher=Springer-Verlag | location=New York | page=442 | date=2000}}</ref><ref name=McDonald_etal_2001>{{cite journal | author1=McDonald, M. A. | author2=Calambokidis, J. | author3=Teranishi, A. M. | author4=Hildebrand, J. A. | title=The acoustic calls of blue whales off California with gender data | journal=Journal of the Acoustical Society of America | volume=109 | issue=4 | pages=1728–1735 | date=2001| doi=10.1121/1.1353593 | pmid=11325141 | bibcode=2001ASAJ..109.1728M | url=http://www.escholarship.org/uc/item/6vg9t2g7 }}</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>{{cite journal | author1=Oleson, E. M. | author2=Calambokidis, J. | author3=Burgess, W. C. | author4=McDonald, M. A. | author5=LeDuc, C. A. | author6=Hildebrand, J. A. | title=Behavioral context of call production by eastern North Pacific blue whales | journal= [[Marine Ecology Progress Series]]| volume=330 | pages=269–284 | date=2007| doi=10.3354/meps330269 | bibcode=2007MEPS..330..269O | doi-access=free }}</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>{{cite journal | author1=Lewis, L. A. | author2=Calambokidis, J. | author3=Stimpert, A. K. | author4=Fahlbusch, J. | author5=Friedlaender, A. S. | author6=McKenna, M. F. | author7=Mesnick, S. | author8=Oleson, E. M. | author9=Southall, B. L. | author10=Szesciorka, A. S. | author11=Sirovic, A. | title=Context-dependent variability in blue whale acoustic behaviour | journal=[[Royal Society Open Science]] | volume=5 | issue=8 | page=1080241 | date=2018 | doi=10.1098/rsos.180241| pmid=30225013 | pmc=6124089 }}</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&nbsp;Hz pulsive call, and is normally 17.9 ± 5.2 seconds long. The second unit is a 55.9 to 72.4&nbsp;Hz [[Frequency modulation|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&nbsp;Hz.<ref name=Stafford_etal_2010>{{cite journal | author1=Stafford, K. M. | author2=Chapp, E. | author3=Bohnenstiel, D. | author4=Tolstoy, M. | author4-link=Maya Tolstoy | title=Seasonal detection of three types of "pygmy" blue whale calls in the Indian Ocean | journal=Marine Mammal Science | volume=27 | issue=4 | pages=828–840 | date=2010| doi=10.1111/j.1748-7692.2010.00437.x }}</ref> A blue whale call recorded off Madagascar, a two-unit phrase,<ref name=Ljungblad_etal_1998>{{cite report | author1=Ljungblad, D. K. | author2=Clark, C. W. | author3=Shimada, H. | title=A comparison of sounds attributed to pygmy blue whales (''Balaenoptera musculus brevicauda'') recorded south of the Madagascar Plateau and those attributed to 'true' blue whales (''Balaenoptera musculus'') recorded off Antarctica | publisher=International Whaling Commission | volume=48 | pages=439–442 | date=1998}}</ref> consists of 5–7 pulses with a [[center frequency]] of 35.1 ± 0.7&nbsp;Hz lasting 4.4 ± 0.5 seconds proceeding a 35 ± 0&nbsp;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&nbsp;Hz tone, and then a 1-second downsweep to 19&nbsp;Hz, followed by a downsweep further to 18&nbsp;Hz.<ref name=Sirovic_etal_2004>{{cite journal | author1=Sirovic, A. | author2=Hildebrand, J. A. | author3=Wiggins, S. M. | author4=McDonald, M. A. | author5=Moore, S. E. | author6=Thiele, D. | title=Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula | journal=[[Deep Sea Research Part II: Topical Studies in Oceanography]] | volume=51 | issue=17–19 | pages=2327–2344 | date=2004| doi=10.1016/j.dsr2.2004.08.005 | bibcode=2004DSRII..51.2327S }}</ref><ref name=Rankin_etal_2005/> Other vocalizations include 1–4 second long, frequency-modulated calls with a frequency of 80 and 38&nbsp;Hz.<ref name=Rankin_etal_2005>{{cite journal | author1=Rankin, S. | author2=Ljungblad, D. | author3=Clark, C. | author4=Kato, H. | title=Vocalisations of Antarctic blue whales, ''Balaenoptera musculus intermedia'', recorded during the 2001/2002 and 2002/2003 IWC/SOWER circumpolar cruises, Area V, Antarctica | journal=Journal of Cetacean Research and Management | volume=7 | pages=13–20 | date=2023| doi=10.47536/jcrm.v7i1.752 | s2cid=43993242 | doi-access=free }}</ref><ref name=Sirovic_etal_2006>{{cite journal | author1=Sirovic, A. | author2=Hildebrand, J. A. | author3=Thiele, D. | title=Baleen whales in the Scotia Sea in January and February 2003 | journal=Journal of Cetacean Research and Management | volume=8 | pages=161–171 | date=2006| doi=10.47536/jcrm.v8i2.712 | s2cid=251277044 | doi-access=free }}</ref>

There is evidence that some blue whale songs have temporally declined in tonal frequency.<ref name=Nieukirk_etal_2005>{{cite conference | author1=Nieukirk, S. L. | author2=Mellinger, D. K. | author3=Hildebrand, J. A. | author4=McDonald, M. A. | author5=Dziak, R. P. | title=Downward shift in the frequency of blue whale vocalizations | conference=16th Biennial Conference on the Biology of Marine Mammals | location=San Diego, CA | page=205 | date=2005}}</ref><ref name=McDonald_etal_2009>{{cite journal | author1=McDonald, M. A. | author2=Hildebrand, J. A. | author3=Mesnick, S. | title=Worldwide decline in tonal frequencies of blue whale songs | journal=Endangered Species Research | volume=9 | pages=13–21 | date=2009| doi=10.3354/esr00217 | doi-access=free }}</ref><ref name=Leroy_etal_2018>{{cite journal | author1=Leroy, E. C. | author2=Royer, J.-Y. | author3=Bonnel, J. | author4=Samaran, F. | title=Long-term and seasonal changes of large whale call frequency in the southern Indian Ocean | journal=[[Journal of Geophysical Research: Oceans]] | volume=123 | issue=11 | pages=8568–8580 | date=2018| doi=10.1029/2018JC014352 | bibcode=2018JGRC..123.8568L | s2cid=135201588 | url=https://archimer.ifremer.fr/doc/00516/62730/ | doi-access=free | hdl=1912/10837 | hdl-access=free }}</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>{{cite journal | author1=Sears, R. | title=The Cortez blues | journal=Whalewatcher | volume=24 | pages=12–15 | date=1990}}</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>{{cite journal | author1=Mehta, A. V. | author2=Allen, J. M. | author3=Constantine, R. | author4=Garrigue, C. | author5=Jann, B. | author6=Jenner, C. | author7=Marx, M. K. | author8=Matkin, C. O. | author9=Mattila, D. K. | author10=Minton, G. | author11=Mizroch, S. A. | author12=Olavarría, C. | author13=Robbins, J. | author14=Russell, K. G. | author15=Seton, R. E. | title=Baleen whales are not important as prey for orcas (''Orcinus orca'') in high latitudes | journal=Marine Ecology Progress Series | volume=348 | pages=297–307 | date=2007| doi=10.3354/meps07015 | doi-access=free | hdl=1912/4520 | hdl-access=free }}</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>{{cite journal | author1=Cotton, B. C. | title=Killer whales in South Australia | journal=[[Australian Zoologist]] | volume=10 | pages=293–294 | date=1944}}</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>{{cite journal | author1=Tarpy, C. | title=Killer whale attack! | journal=National Geographic Magazine | volume=155 | pages=542–545| date=1979}}</ref> Four more blue whales were documented as being chased by a group of orcas between 1982 and 2003.<ref name=Ford_Reeves_2008>{{cite journal | author1=Ford, J. K. B. | author2=Reeves, R. | title=Fight or flight: antipredator strategies of baleen whales | journal=[[Mammal Review]] | volume=38 | issue=1 | pages=50–86 | date=2008| doi=10.1111/j.1365-2907.2008.00118.x }}</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>{{cite journal | author1=Pitman, R. | author2=Fearnbach, H. | author3=LeDuc, R. | author4=Gilpatrick, J. W. | author5=Ford, J. K. B. | author6=Balance, L. T. | title=Killer whales preying on a blue whale calf on the Costa Rica Dome: Genetics, morphometrics, vocalizations and composition of the group | journal=Journal of Cetacean Research and Management | volume=9 | pages=151–158 | date=2023| issue=2 | doi=10.47536/jcrm.v9i2.683 | s2cid=257138804 | doi-access=free }}</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>{{cite web | url=https://www.livescience.com/43879-killer-whales-attack-blue-whale-video.html | title=Killer Whales Bully Lone Blue Whale in Rare Video | date=5 March 2014 | publisher=[[Live Science]] | access-date=23 December 2019}}</ref> A similar incident was recorded by a drone in Monterey Bay in May 2017.<ref>{{cite web | url=https://www.nationalgeographic.com/news/2017/05/killer-whale-attacks-blue-whale-monterey-drone-video | archive-url=https://web.archive.org/web/20191231040658/https://www.nationalgeographic.com/news/2017/05/killer-whale-attacks-blue-whale-monterey-drone-video/ | url-status=dead | archive-date=31 December 2019 | title=Killer Whales Attacked a Blue Whale—Here's the Surprising Reason Why | date=25 May 2017 | publisher=National Geographic | access-date=23 December 2019}}</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 {{convert|18|–|22|m|sp=us}}.<ref>{{cite journal|author1=Totterdell, J. A.|author2=Wellard, R.|author3=Reeves, I. M.|author4=Elsdon, B.|author5=Markovic, P.|author6=Yoshida, M.|author7=Fairchild, A.|author8=Sharp, G.|author9=Pitman, R.|year=2022|title=The first three records of killer whales (''Orcinus orca'') killing and eating blue whales (''Balaenoptera musculus'')|journal=Marine Mammal Science|volume=38 |issue=3 |pages=1286–1301 |doi=10.1111/mms.12906|bibcode=2022MMamS..38.1286T | s2cid=246167673 }}</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. [[Barnacle]]s 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>{{cite journal|last1=Hermosilla|first1=C|last2=Silva|first2=L. M. R.|last3=Prieto|first3=R|last4=Kleinertz|first4=S|last5=Taubert|first5=A|last6=Silva|first6=M. A.|year=2015|title=Endo- and ectoparasites of large whales (Cetartiodactyla: Balaenopteridae, Physeteridae): Overcoming difficulties in obtaining appropriate samples by non- and minimally-invasive methods|journal=International Journal for Parasitology: Parasites and Wildlife|volume=4|issue=3|pages=414–420|doi=10.1016/j.ijppaw.2015.11.002|pmid=26835249|pmc=4699982|bibcode=2015IJPPW...4..414H}}</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>{{cite journal | author1=Gambell, R. | title=The blue whale | journal=Biologist | volume=26 | pages=209–215 | date=1979}}</ref><ref name=Best_1993>{{cite journal | author1=Best, P. B. | title=Increase rates in severely depleted stocks of baleen whales | journal=ICES J. Mar. Sci. | volume=50 | issue=2 | pages=169–186 | date=1993| doi=10.1006/jmsc.1993.1018 | bibcode=1993ICJMS..50..169B }}</ref> The protected status of North Atlantic blue whales was not recognized by Iceland until 1960.<ref name="Sigurjónsson_1988">{{cite journal | author1=Sigurjónsson, J. | title=Operational factors of the Icelandic large whale fishery | journal=Reports of the International Whaling Commission| volume=38 | pages=327–333 | date=1988}}</ref> In the United States, the species is protected under the [[Endangered Species Act]].<ref name=NOAAblue/>

Blue whales are formally classified as [[Endangered species|endangered]] under both the U.S. [[Endangered Species Act]]<ref>{{cite web |url=https://ecos.fws.gov/docs/federal_register/fr21.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ecos.fws.gov/docs/federal_register/fr21.pdf |archive-date=9 October 2022 |url-status=live |title=Part 17 – Conservation of Endangered Species and Other Fish or Wildlife (First List of Endangered Foreign Fish and Wildlife as Appendix A) | date=2 June 1970 |publisher=[[U.S. Fish & Wildlife Service]] |access-date=24 December 2019}}</ref> and the [[IUCN Red List]].<ref name="iucn"/> They are also listed on Appendix&nbsp;I under the [[Convention on International Trade in Endangered Species of Wild Fauna and Flora]] (CITES)<ref>{{cite web | url=https://www.cites.org/eng/app/appendices.php | title=Appendices | date=26 November 2019 | publisher=Convention on International Trade in Endangered Species of Wild Fauna and Flora | access-date=24 December 2019}}</ref> and the [[Convention on the Conservation of Migratory Species of Wild Animals]].<ref>{{cite web | url=https://www.cms.int/sites/default/files/instrument/CMS-text.en_.PDF | title=Convention on the Conservation of Migratory Species of Wild Animals | date=23 June 1979 | publisher=[[United Nations Environment Programme]] | access-date=24 December 2019 | archive-url=https://web.archive.org/web/20200502225536/https://www.cms.int/sites/default/files/instrument/CMS-text.en_.PDF | archive-date=2 May 2020 | url-status=dead }}</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>{{cite journal | author1=Samaran, F. | author2=Stafford, K. M. | author3=Branch, T. A. | author4=Gedamke, J. | author5=Royer, Y.-J. | author6=Dziak, R. P. | author7=Guinet, C. | title=Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean | journal=PLOS ONE | volume=8 | issue=8 | page=e71561 | date=2013| bibcode=2013PLoSO...871561S | doi=10.1371/journal.pone.0071561 | pmid=23967221 | pmc=3742792 | doi-access=free }}</ref><ref>{{cite web | url=https://iucn-csg.org/35-updated-cetacean-red-list-assessments-published-in-nov-2018/ | title=Blue Whale | date=6 December 2018 | publisher=International Union for Conservation | access-date= 24 December 2019}}</ref>

===Threats===
[[File:FMIB 34640 Large Hump-Back -sic- Whale, 83 Feet Long.jpeg|thumb|Dead blue whale on [[flensing]] platform]]
In 2017, [[DNA]] evidence was used to identify whale bones at [[Iceland]]ic 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>{{cite news |last1=Andrew |first1=Chapman |title=How Viking-Age Hunters Took Down the Biggest Animal on Earth |url=https://hakaimagazine.com/features/how-viking-age-hunters-took-down-the-biggest-animal-on-earth/ |access-date=7 May 2024 |work=Newsweek |date=28 February 2025}}</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>{{cite book |author=Darby, Andrew |url=https://archive.org/details/harpoonintoheart00darb/page/38/mode/2up |title=Harpoon Into the Heart of Whaling |publisher=Hachette Books |year=2009 |isbn=9780786732005 |pages=38–39 |url-access=registration}}</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>{{cite web|title=Blue whale – ''Balaenoptera musculus''|publisher=International Whaling Commission|access-date=25 February 2022|url=https://iwc.int/blue-whale}}</ref> However, the [[Soviet Union]] continued to illegally hunt blue whales and other species up until the 1970s.<ref>{{cite journal|author1=Ivashchenko, Y.|author2=Clapham, P. J.|author3=Brownell, R.|year=2011|title=Soviet Illegal Whaling: The Devil and the Details|journal=Marine Fisheries Review|volume=73|issue=1|pages=1–19|url=https://aquadocs.org/bitstream/handle/1834/26267/mfr7331.pdf?sequence=1&isAllowed=y|access-date=26 January 2023|archive-date=22 March 2022|archive-url=https://web.archive.org/web/20220322075344/https://aquadocs.org/bitstream/handle/1834/26267/mfr7331.pdf?sequence=1&isAllowed=y}}</ref>
[[File:Blue whale ship strike death.jpg|thumb|right|Researchers examine a dead blue whale killed by collision with a ship]]
[[Environmental impact of shipping#Wildlife collisions|Ship strikes]] are a significant mortality factor for blue whales, especially off the [[U.S. West Coast]].<ref name="Berman-Kowalewski_etal_2010">{{cite journal | author1=Berman-Kowalewski, M. | author2=Gulland, F. | author3=Wilkin, S. | author4=Calambokidis, J. | author5=Mate, B. | author6=Cordaro, J. | author7=Rotstein, D. | author8=St. Leger, J. | author9=Collins, P. | author10=Fahy, K. | author11=Dover, S. | s2cid=86304413 | title=Association between blue whale mortality and ship strikes along the California coast | journal=Aquatic Mammals | volume=36 | issue=1 | pages=59–66 | date=2010| doi=10.1578/AM.36.1.2010.59 }}</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>{{cite report | author1=Abramson, L. | author2=Polefka, S. | author3=Hastings, S. | author4=Bor, K. | title=Reducing the Threat of Ship Strikes on Large Cetaceans in the Santa Barbara Channel Region and Channel Islands National Marine Sanctuary: Recommendations and Case Studies | publisher=Channel Islands National Marine Sanctuary Advisory Council | pages=1–73 | date=2009}}</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>{{cite journal | author1=de Vos, A. | author2=Brownell, R. L. Jr. | author3=Tershy, B. R. | author4=Croll, D. A. | title=Anthropogenic threats and conservation needs of blue whales, "Balaenoptera musculus indica", around Sri Lanka | journal=J. Mar. Biol. | volume=2016 | issue=8420846 | pages=1–12 | date=2016| doi=10.1155/2016/8420846 | doi-access=free }}</ref> Here, strikes caused the deaths of eleven blue whales in 2010 and 2012,<ref name=Priyadarshana_etal_2015>{{cite report | author1=Priyadarshana, T. | author2=Randage, R. | author3=Alling, A. | author4=Calderan, S. | author5=Gordon, J. | author6=Leaper, R. | author7=Porter, L. | title=An update on work related to ship strike risk to Blue whales off southern Sri Lanka | publisher=The International Whaling Commission | volume=SC66A | date=2015}}</ref> and at least two in 2014.<ref name=Randage_etal_2014>{{cite journal | author1=Randage, S. M. | author2=Alling, A. | author3=Currier, K. | author4=Heywood, E. | title=Review of the Sri Lanka blue whale (''Balaenoptera musculus'') with observations on its distribution in the shipping lane | journal=Journal of Cetacean Research and Management | year=2023 | volume=14 | pages=43–49 | doi=10.47536/jcrm.v14i1.522 | s2cid=46399716 | doi-access=free }}</ref> Ship-strike mortality claimed the lives of two blue whales off southern Chile in the 2010s.<ref name=Brownell_etal_2014>{{cite report | author1=Brownell, R. L. Jr. | author2=Cabrera, E. | author3=Galletti-Vernazzani, B. | title=Dead blue whale in Puerto Montt, Chile: Another case of ship collision mortality | publisher=International Whaling Commission | volume=SC/65b/HIM08 | date=2014}}</ref><ref name=IWC_2017>{{cite report | author1=International whaling Commission | title=Report of the Scientific Committee | publisher=International Whaling Commission | page=136 | date=2017}}</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>{{cite journal | author1=Redfern, J. V. | author2=McKenna, M. F. | author3=Moore, T. J. | author4=Calambokidis, J. | author5=Deangelis, M. L. | author6=Becker, E. A. | author7=Barlow, J. | author8=Forney, K. A. | author9=Fiedler, P. C. | author10=Chivers, S. J. | title=Assessing the risk of ships striking large whales in marine spatial planning | journal=[[Conservation Biology (journal)|Conservation Biology]] | volume=22 | issue=2 | pages=292–302 | date=2013| doi=10.1111/cobi.12029 | pmid=23521668 | bibcode=2013ConBi..27..292R | s2cid=17833403 }}</ref><ref name=Dransfield_etal_2014>{{cite journal | author1=Dransfield, A. | author2=Hines, E. | author3=McGowan, J. | author4=Holzman, B. | author5=Nur, N. | author6=Elliott, M. | author7=Howar, J. | author8=Jacncke, J. | title=Where the whales are: using habitat modeling to support changes in shipping regulations within National Marine Sanctuaries in Central California | journal=Endanger Species Res | volume=26 | issue=1 | pages=39–57 | date=2014| doi=10.3354/esr00627 | doi-access=free }}</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>{{cite report | author1=Carretta, J. V. | author2=Muto, M. M. | author3=Greenman, J. | author4=Wilkinson, K. | author5=Viezbicke, J. | author6=Jannot, J. | title=Sources of human-related injury and mortality for U.S. Pacific west coast marine mammal stock assessments, 2011– 2015 | publisher=NOAA | volume=PSRG-2017-07 | date=2017}}</ref> Three more entanglement cases were reported in 2016.<ref name=NMFS_2017>{{cite report | author1=NMFS | title=National Report on Large Whale Entanglements | publisher=NOAA | url=https://www.fisheries.noaa.gov/resource/document/national-report-large-whale-entanglements-2017 | date=2017}}</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>{{cite book | author1=de Vos, A. | title=Deepwater Horizon oil spill: Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement | chapter=Marine life on the line | editor1-last=Braun | editor1-first=D. | publisher=National Geographic | page=685 | chapter-url=http://www.gulfspillrestoration.noaa.gov/restoration-planning/gulf-plan | date=2015}}</ref>

Increasing [[Anthropogenic hazard|man-made]] underwater noise impacts blue whales.<ref name=Southall_etal_2018>{{cite journal | author1=Southall, B. L. | author2=Hatch, L. | author3=Scholik-Schlomer, A. | author4=Bergmann, T. | author5=Jasny, M. | author6=Metcalf, K. | author7=Weilgart, L. | author8=Wright, A. J. | author9=Perera, M. E. | title=Reducing noise from large commercial ships: progress and partnerships | journal=Proc. Mar. Saf. Sec. Council | volume=1 | pages=58–65 | date=2018}}</ref><ref name=Wiggins_etal_2001>{{cite journal | author1=Wiggins, S. M. | author2=Oleson, E. M. | author3=Hildebrand, J. A. | title=Blue whale call intensity varies with ambient noise level | journal=[[Journal of the Acoustical Society of America]] | volume=110 | issue=5 | page=2771 | date=2001| bibcode=2001ASAJ..110.2771W | doi=10.1121/1.4777708 }}</ref> They may be exposed to noise from commercial shipping<ref name=McKenna_etal_2012>{{cite journal | author1=McKenna, M. F. | author2=Ross, D. | author3=Wiggins, S. M. | author4=Hildebrand, J. A. | s2cid=9474116 | title=Underwater radiated noise from modern commercial ships | journal=The Journal of the Acoustical Society of America | volume=131 | issue=1 | pages=92–103 | date=2012| doi=10.1121/1.3664100 | pmid=22280574 | bibcode=2012ASAJ..131...92M }}</ref><ref name=Szesciorka_etal_2019>{{cite journal | author1=Szesciorka, A. R. | author2=Allen, A. N. | author3=Calambokidis, J. | author4=Fahlbusch, J. | author5=McKenna, M. F. | author6=Southall, B. L. | title=A case study of a near vessel strike of a blue whale: perceptual cues and fine-scale aspects of behavioral avoidance | journal=Front. Mar. Sci. | volume=6 | issue=761 | pages=1–10 | date=2019| doi=10.3389/fmars.2019.00761 | doi-access=free }}</ref> and seismic surveys as a part of oil and gas exploration.<ref name=DiIorio_Ckark_2009>{{cite journal | author1=Di Iorio, L. | author2=Clark, C. W. | title=Exposure to seismic survey alters blue whale acoustic communication | journal=Biology Letters | volume=6 | issue=1 | pages=1–4 | date=2009}}</ref><ref name=McDonald_etal_1995>{{cite journal | author1=McDonald, M. A. | author2=Hildebrand, J. A. | author3=Webb, S. C. | s2cid=3829165 | title=Blue and fin whales observed on a seafloor array in the Northeast Pacific | journal=Journal of the Acoustical Society of America | volume=98 | issue=2 | pages=712–721 | date=1995| doi=10.1121/1.413565 | pmid=7642810 | bibcode=1995ASAJ...98..712M | url=https://escholarship.org/uc/item/2sx2b1cj }}</ref> Blue whales in the [[Southern California Bight]] decreased calling in the presence of mid-frequency active (MFA) [[sonar]].<ref name="Melcón_etal_2012">{{cite journal | author1=Melcón, M. L. | author2=Cummins, A. J. | author3=Kerosky, S. M. | author4=Roche, L. K. | author5=Wiggins, S. M. | author6=Hildebrand, J. A. | title=Blue Whales Respond to Anthropogenic Noise | journal=PLOS ONE | volume=7 | issue=2 | page=e32681 | date=2012| doi=10.1371/journal.pone.0032681 | pmid=22393434 | pmc=3290562 | bibcode=2012PLoSO...732681M | doi-access=free }}</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>{{cite journal | author1=Southall, B. L. | author2=DeRuiter, S. L. | author3=Friedlaender, A. | author4=Stimpert, A. K. | author5=Goldbogen, J. A. | author6=Hazen, E. | author7=Casey, C. | author8=Fregosi, S. | author9=Cade, D. E. | author10=Allen, A. N. | author11=Harris, C. M. | author12=Schorr, G. | author13=Moretti, D. | title=Behavioral responses of individual blue whales (''Balaenoptera musculus'') to mid-frequency military sonar | journal=[[The Journal of Experimental Biology]]| volume=222 | issue=jeb190637 | pages=jeb190637 | date=2019| doi=10.1242/jeb.190637 | pmid=30833464 | doi-access=free | bibcode=2019JExpB.222B0637S | hdl=10023/19592 | hdl-access=free }}</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>{{cite journal | author1=O'Shea, T. J. | author2=Brownell, R. L. | title=Organochlorine and metal contaminants in baleen whales:a review and evaluation of conservation implications | journal=[[Science of the Total Environment]]| volume=154 | issue=2–3 | pages=179–200 | date=1994| doi=10.1016/0048-9697(94)90087-6 | pmid=7973606 | bibcode=1994ScTEn.154..179O }}</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 in aquatic mammals|maternal transfer]] occurred during gestation and/or lactation.<ref name=Trumble_etal_2013>{{cite journal | author1=Trumble, S. J. | author2=Robinson, E. M. | author3=Berman-Kowalewski, M. | author4=Potter, C. W. | author5=Usenko, S. | title=Blue whale earplug reveals lifetime contaminant exposure and hormone profiles | journal=Proceedings of the National Academy of Sciences | volume=110 | issue=42 | pages=16922–16926 | date=2013| doi=10.1073/pnas.1311418110 | bibcode=2013PNAS..11016922T | doi-access=free | pmid=24043814 | pmc=3801066 }}</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>{{cite journal | author1=Metcalfe, C. D. | author2=Koenig, B. G. | author3=Metcalfe, T. L. | author4=Paterson, G. | author5=Sears, R. | title=Intra- and inter-species differences in persistent organic contaminants in the blubber of blue whales and humpback whales from the Gulf of St. Lawrence, Canada | journal=Marine Environmental Research| volume=57 | issue=4 | pages=245–260 | date=2004| doi=10.1016/j.marenvres.2003.08.003 | pmid=14749058 | bibcode=2004MarER..57..245M }}</ref>

== See also ==
{{Portal|Cetaceans|Mammals|Marine life}}
* [[Largest organisms]]
* [[List of cetaceans]]
* [[List of largest mammals]]
* [[List of whale vocalizations]]

==Note==
{{notelist}}

== References ==
{{Reflist}}

== Further reading ==
{{Refbegin}}
* {{cite book
| title = Blue Whales
| author1 = Calambokidis, J.
| author2 = Steiger, G.
| name-list-style = amp
| year = 1998
| publisher = [[Voyageur Press]]
| isbn = 978-0-89658-338-2
| url-access = registration
| url = https://archive.org/details/bluewhales0000cala
}}
* {{cite web
| title=Blue whale, ''Balaenoptera musculus''
| work = MarineBio.org
| url = http://marinebio.org/species.asp?id=41
| access-date = 21 April 2006}}
* [http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/bluewhale.htm NOAA Fisheries, Office of Protected Resources] Blue whale biology & status
{{Refend}}

== External links ==
{{Spoken Wikipedia|Blue whale.ogg|date=13 April 2006}}
* [https://web.archive.org/web/20150226002906/http://www.birds.cornell.edu/brp/listen-to-project-sounds/blue-whale Blue whale vocalizations] – Cornell Lab of Ornithology—Bioacoustics Research Program (archived 26 February 2015)
* [http://www.bbc.co.uk/nature/species/Blue_Whale Blue whale video clips and news from the BBC – BBC Wildlife Finder]
* [http://voicesinthesea.ucsd.edu/species/baleenWhales/blue.html Voices in the Sea – Sounds of the Blue Whale]
* [https://www.fisheries.noaa.gov/species/blue-whale NOAA Stock Assessments]
* [http://www.bbcamerica.com/shows/the-hunt/video-extras/life-of-a-hunter-blue-whale Life of a Hunter: Blue Whale] {{Webarchive|url=https://web.archive.org/web/20191231040638/http://www.bbcamerica.com/shows/the-hunt/video-extras/life-of-a-hunter-blue-whale |date=31 December 2019 }} – BBC America
* [http://www.bbcamerica.com/shows/the-hunt/season-1/episode-07-living-with-predators Living With Predators] – BBC America

{{Cetacea|M.}}
{{Taxonbar|from=Q42196}}
{{Authority control}}

[[Category:Blue whales| ]]
[[Category:Balaenoptera]]
[[Category:Mammals described in 1758]]
[[Category:Conservation-reliant species]]
[[Category:Cosmopolitan mammals]]
[[Category:Biological records]]
[[Category:ESA endangered species]]
[[Category:Taxa named by Carl Linnaeus]]