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Balenottera azzurra [1]
Stato di conservazione
In pericolo[2]
Classificazione scientifica
RegnoAnimalia
PhylumChordata
ClasseMammalia
OrdineCetacea
SottordineMysticeti
FamigliaBalaenopteridae
GenereBalaenoptera
SpecieB. musculus
Nomenclatura binomiale
Balaenoptera musculus
Linnaeus, 1758
Areale
  • B. m. musculus Linnaeus, 1758
  • B. m. brevicauda Ichihara, 1966
  • B. m. indica Blyth, 1859
  • B. m. intermedia Burmeister, 1871

La balenottera azzurra (Balaenoptera musculus Linnaeus, 1758) è un mammifero marino appartenente al sottordine dei Misticeti (le cosiddette «balene con i fanoni») [3] . Con oltre 33 metri di lunghezza e 180 tonnellate [4] di peso, è il più grande animale conosciuto mai vissuto sul Pianeta [5] .

Lungo e slanciato, il corpo della balenottera azzurra può assumere varie tonalità grigio-bluastre sul dorso, ma si fa più chiaro sul ventre [6] . Ne esistono almeno tre sottospecie riconosciute: B. m. musculus dell'Atlantico e del Pacifico settentrionali, B. m. intermedia dell'Oceano Australe e B. m. brevicauda (nota anche come balenottera azzurra pigmea) dell'Oceano Indiano e del Pacifico meridionale. Alcuni considerano una sottospecie anche B. m. indica, anch'essa dell'Oceano Indiano. Come quella degli altri Misticeti, anche la sua dieta consiste quasi esclusivamente dei piccoli crostacei noti come krill [7] .

Fino agli inizi del XX secolo la balenottera azzurra era numerosa in quasi tutti gli oceani. Per più di 40 anni, però, è stata cacciata dai balenieri fin quasi all'estinzione; la comunità internazionale la dichiarò specie protetta solamente nel 1966. Secondo un rapporto del 2002 in tutto il mondo vi sarebbero attualmente dai 5000 ai 12.000 esemplari [8], suddivisi in almeno cinque gruppi. In base a ricerche più recenti effettuate sulla sottospecie pigmea si ipotizza che tali numeri, però, siano stati un po' troppo sottostimati [9] . Prima della caccia, la popolazione più numerosa era quella antartica, forte di circa 239.000 esemplari (le stime vanno da 202.000 a 311.000) [10] . Ora rimangono solo popolazioni molto più piccole (di circa 2000 esemplari l'una), concentrate nel Pacifico nord-orientale e negli oceani Australe e Indiano. Due popolazioni meno numerose si incontrano nell'Atlantico settentrionale ed almeno altre due nell'emisfero australe.

Tassonomia

  Lo stesso argomento in dettaglio: Evoluzione dei cetacei.

La balenottera azzurra appartiene alla famiglia dei Balenotteridi, un gruppo che comprende la megattera, la balenottera comune, la balenottera di Bryde, la balenottera boreale e la balenottera minore [3] . Si ritiene che i Balenotteridi si siano separati dalle altre famiglie del sottordine dei Misticeti non più tardi dell'Oligocene Medio. Tuttavia, il momento esatto in cui i membri delle varie famiglie si sono separate tra di loro è ancora ignoto.

Solitamente la balenottera azzurra viene classificata come una delle otto specie del genere Balaenoptera; alcuni autori, però, la pongono in un genere monotipico a parte, Sibbaldus [11] , ma tale suddivisione non è molto accettata [12] . L'analisi delle sequenze del DNA indica che sotto un punto di vista filogenetico la balenottera azzurra è più strettamente imparentata con la balenottera boreale (Balaenoptera borealis) e la balenottera di Bryde (Balaenoptera brydei) che con le altre specie del genere Balaenoptera, e più imparentata con la megattera (Megaptera) e la balena grigia (Eschrichtius) che con le balenottere minori (Balaenoptera acutorostrata e Balaenoptera bonaerensis) [13][14] . Se ulteriori ricerche confermeranno queste relazioni sarà necessario rivedere tutta la classificazione delle balenottere.

In natura vi sono stati almeno 11 casi documentati di ibridi adulti di balenottera azzurra e balenottera comune. Arnason e Gullberg hanno descritto la distanza genetica che intercorre tra queste due specie pari a quella tra l'uomo e il gorilla [15] . Alcuni ricercatori sostengono anche di aver fotografato, al largo delle Figi, un ibrido tra balenottera azzurra e megattera [16] .

Il nome specifico musculus è di origine latina e significa «muscoloso», sebbene altri lo interpritino anche come «piccolo topo» [17] . Linneo, che classificò per primo la specie nel suo Systema Naturae del 1758 [18] , potrebbe aver attributo alla specie questo nome proprio giocando sull'ironicità del doppio senso [19] . Herman Melville, nel suo romanzo Moby-Dick, chiamò questa specie sulphur-bottom a causa della tinta marrone-arancio o gialla delle sue regioni inferiori, dovuta ad una sottile pellicola di Diatomee presente sulla pelle. Tra gli altri nomi comuni con cui questa specie veniva chiamata ricordiamo balenottera di Sibbald (in onore di Sir Robert Sibbald), grande balena azzurra e grande balenottera settentrionale. Tutti questi nomi sono attualmente caduti in disuso.

Gli autori suddividono la specie in tre o quattro sottospecie: B. m. musculus, la balenottera azzurra settentrionale, a cui appartengono le popolazioni dell'Atlantico e del Pacifico settentrionali, B. m. intermedia, la balenottera azzurra meridionale, dell'Oceano Australe, B. m. brevicauda, la balenottera azzurra pigmea, dell'Oceano Indiano e del Pacifico Meridionale [20] , e la più discussa B. m. indica, la grande balenottera indiana, anch'essa dell'Oceano Indiano, ma che potrebbe essere, sebbene sia stata descritta prima, una particolare forma di B. m. brevicauda [12] .

Descrizione e comportamento

 
Una balenottera azzurra sbatte la coda sulla superficie del mare
 
Un esemplare adulto
 
Veduta aerea di una balenottera azzurra in cui si vedono bene anche entrambe le pinne pettorali
 
Il soffio di una balenottera azzurra
 
La piccola pinna dorsale di questo esemplare è appena visibile all'estrema sinistra

La balenottera azzurra ha un corpo lungo e affusolato che sembra sia stato quasi «stirato», rispetto a quello di altre balene, più tozzo [21] . La testa è appiattita e a forma di «U» e presenta una cresta dorsale che va dallo sfiatatoio alla sommità del labbro superiore [21] . La parte anteriore della bocca è ricca di fanoni; circa 300 di queste strutture (ognuna delle quali lunga circa un metro) [21] pendono dalla mascella superiore, estendendosi all'interno della bocca per quasi mezzo metro. Lungo la gola, parallelamente alla lunghezza del corpo, si trovano dai 60 ai 90 solchi (detti pieghe ventrali). Queste pieghe servono a buttar fuori l'acqua dalla bocca durante la nutrizione (vedi oltre).

La pinna dorsale è piccola [21] ed è visibile solamente quando la balenottera si immerge. Situata a circa tre-quarti della lunghezza del corpo, varia nella forma da individuo a individuo: alcuni presentano solo un moncone appena percettibile, mentre altri possono averla più lunga e falcata. Quando emerge per respirare, la balenottera azzurra fa emergere una maggior superficie della schiena e dello sfiatatoio di quanto non facciano altre grandi balenottere, come quella comune o quella boreale. Gli studiosi possono utilizzare questa caratteristica per differenziare in mare le varie specie. Alcuni esemplari dell'Atlantico e del Pacifico settentrionali quando si immergono sbattono anche la coda sulla superficie dell'acqua. Quando respira, questa specie emette uno spettacolare soffio verticale e colonnare che può raggiungere anche i 12 m, sebbene generalmente sia di 9 m. La capacità dei suoi polmoni è di 5000 litri. Possiede due sfiatatoi gemelli protetti da una sorta di grosso paraschizzi [21] .

Le pinne pettorali sono lunghe 3 - 4 metri. Il loro margine superiore è grigio con una sottile striscia bianca lungo il margine. Quello inferiore è bianco. La testa e la pinna caudale sono generalmente di colore grigio uniforme. Le regioni inferiori, e talvolta anche le pinne pettorali, sono solitamente chiazzate. Il grado di screziatura varia però moltissimo da individuo a individuo. Alcuni possono essere di un color grigio ardesia uniforme, altri di un miscuglio di azzurro scuro, grigio e nero, altri ancora quasi completamente macchiati [3] .

Su brevi distanze, solitamente mentre interagiscono con altri esemplari, le balenottere azzurre possono raggiungere anche velocità di 50 km/h; la loro velocità tipica, però, è di 20 km/h [3] . Mentre si nutrono si spostano molto lentamente, a velocità di 5 km/h.

Le balenottere azzurre vivono quasi sempre da sole o in coppia. Non si sa per quanto tempo le coppie rimangano unite. In alcune località dove vi è un'alta concentrazione di cibo, in aree anche relativamente poco estese, sono state viste fino a 50 balenottere. Tuttavia, a differenza di altre specie, non forma mai grandi gruppi numerosi.

Size

 
A 19-foot-long blue whale skull in the collections of the Smithsonian Museum of Natural History.

Blue whales are difficult to weigh because of their size. Most blue whales killed by whalers were not weighed whole, but cut up into manageable pieces first. This caused an underestimate of the total weight of the whale, due to the loss of blood and other fluids. Nevertheless, measurements between 150–170 tonnellate (170–190 short ton) were recorded of animals up to 27 metri (89 ft) in length. The weight of an individual 30 metri (98 ft) long is believed by the American National Marine Mammal Laboratory (NMML) to be in excess of 180 tonnellate (200 short ton). The largest blue whale accurately weighed by NMML scientists to date was a female that weighed 177 tonnellate (195 short ton).[8]

The blue whale is the largest animal ever known to have lived.[21] The largest known dinosaur of the Mesozoic Era was the Argentinosaurus,[22] which is estimated to have weighed up to 90 tonnellate (99 short ton), though a controversial vertebra of Amphicoelias fragillimus may indicate an animal of up to 122 tonnellate (134 short ton) and 40–60 metri (130–200 ft).[23] Furthermore, there are weight estimates for the very poorly known Bruhathkayosaurus ranging from 140–220 tonnellate (150–240 short ton), besides length estimates up to about 45 metri (148 ft). The extinct fish Leedsichthys may have approached its size.[24] However, complete fossils are difficult to come by, making size comparisons difficult. All these animals are considered to be smaller than the blue whale.

There is some uncertainty about the biggest blue whale ever found, as most data comes from blue whales killed in Antarctic waters during the first half of the twentieth century and was collected by whalers not well-versed in standard zoological measurement techniques. The longest whales ever recorded were two females measuring 33,6–33,3 metri (110–109 ft) respectively.[25] The longest whale measured by scientists at the NMML was 29,9 metri (98 ft).[8]

A blue whale's tongue weighs around 2,7 tonnellate (3,0 short ton)[26] and, when fully expanded, its mouth is large enough to hold up to 90 tonnellate (99 short ton) of food and water.[7] Despite the size of its mouth, the dimensions of its throat are such that a blue whale cannot swallow an object wider than a beach ball.[27] Its heart weighs 600 chilogrammi (1 300 lb) and is the largest known in any animal.[26] A blue whale's aorta is about 23 centimetri (9,1 in) in diameter.[28] During the first seven months of its life, a blue whale calf drinks approximately 400 litres (100 U.S. gallons) of milk every day. Blue whale calves gain weight quickly, as much as 90 chilogrammi (200 lb) every 24 hours. Even at birth, they weigh up to 2 700 chilogrammi (6 000 lb)—the same as a fully grown hippopotamus.[3]

Feeding

Blue whales feed almost exclusively on krill, though they also take small numbers of copepods.[29] The species of this zooplankton eaten by blue whales varies from ocean to ocean. In the North Atlantic, Meganyctiphanes norvegica, Thysanoessa raschii, Thysanoessa inermis and Thysanoessa longicaudata are the usual food;[30][31][32] in the North Pacific, Euphausia pacifica, Thysanoessa inermis, Thysanoessa longipes, Thysanoessa spinifera, Nyctiphanes symplex and Nematoscelis megalops;[33][34][35] and in the Antarctic, Euphausia superba, Euphausia crystallorophias and Euphausia valentin.

An adult blue whale can eat up to 40 million krill in a day.[36] The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3 600 chilogrammi (7 900 lb) of krill in a single day.[29] This daily calorie requirement of an adult blue whale is in the region of 1.5 million.[37]

Because krill move, blue whales typically feed at depths of more than 100 metri (330 ft) during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 20 minutes are common. The longest recorded dive is 36 minutes[38]. The whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. The blue whale also incidentally consumes small fish, crustaceans and squid caught up with krill.[39][40]

Life history

 
A juvenile blue whale with its mother

Mating starts in late autumn and continues to the end of winter.[41] Little is known about mating behaviour or breeding grounds. Females typically give birth once every two to three years at the start of the winter after a gestation period of ten to twelve months.[41] The calf weighs about 2,5 tonnellate (2,8 short ton) and is around 7 metri (23 ft) in length. Blue whale calves drink 380–570 litres (100–150 U.S. gallons) of milk a day. Weaning takes place for about six months, by which time the calf has doubled in length. Sexual maturity is typically reached at eight to ten years, by which time males are at least 20 metri (66 ft) long (or more in the Southern Hemisphere). Females are larger still, reaching sexual maturity at around the age of five, by which they are about 21 metri (69 ft) long.

Scientists estimate that blue whales can live for at least 80 years;[25][41][42] however, since individual records do not date back into the whaling era, this will not be known with certainty for many years. The longest recorded study of a single individual is 34 years, in the north-east Pacific.[38] The whales' only natural predator is the Orca.[43] Studies report that as many as 25% of mature blue whales have scars resulting from Orca attacks.[25] The mortality rate of such attacks is unknown.

Blue whale strandings are extremely uncommon, and, because of the species' social structure, mass strandings are unheard of.[44] However, when strandings do occur, they can become the focus of public interest. In 1920, a blue whale washed up near Bragar on the Isle of Lewis in the Outer Hebrides of Scotland. It had been shot in the head by whalers, but the harpoon had failed to explode. As with other mammals, the fundamental instinct of the whale was to try to carry on breathing at all costs, even though this meant beaching to prevent itself from drowning. Two of the whale's bones were erected just off a main road on Lewis and remain a tourist attraction.[45]

Vocalizations

  Lo stesso argomento in dettaglio: Whale song.
Multimedia relating to the blue whale
Note that the whale calls have been sped up 10x from their original speed.

Estimates made by Cummings and Thompson (1971) suggest that source level of sounds made by blue whales are between 155 and 188 decibels when measured relative to a reference pressure of one micropascal at one metre.[46][47] All blue whale groups make calls at a fundamental frequency of between 10 and 40 Hz; the lowest frequency sound a human can typically perceive is 20 Hz. Blue whale calls last between ten and thirty seconds. Blue whales off the coast of Sri Lanka have been repeatedly recorded making "songs" of four notes duration lasting about two minutes each, reminiscent of the well-known humpback whale songs. Researchers believe that as this phenomenon has not been seen in any other populations, it may be unique to the B. m. brevicauda (Pygmy) subspecies.

The reason for vocalization is unknown. Richardson et al. (1995) discuss six possible reasons:[48]

  1. Maintenance of inter-individual distance
  2. Species and individual recognition
  3. Contextual information transmission (e.g., feeding, alarm, courtship)
  4. Maintenance of social organization (e.g., contact calls between females and males)
  5. Location of topographic features
  6. Location of prey resources

Population and whaling

Hunting era

  Lo stesso argomento in dettaglio: History of whaling.
 
Blue whale populations have declined dramatically due to commercial whaling.

Blue whales are not easy to catch or kill. Their speed and power meant that they were rarely pursued by early whalers, who instead targeted sperm and right whales.[49] In 1864, the Norwegian Svend Foyn equipped a steamboat with harpoons specifically designed for catching large whales.[3] Although initially cumbersome and with a low success rate, Foyn perfected the harpoon gun, and soon several whaling stations were established on the coast of Finnmark in northern Norway. Because of disputes with the local fishermen, the last whaling station in Finnmark was closed down in 1904.

Soon, blue whales were being hunted in Iceland (1883), the Faroe Islands (1894), Newfoundland (1898), and Spitsbergen (1903). In 1904-05 the first blue whales were taken off South Georgia. By 1925, with the advent of the stern slipway in factory ships and the use of steam-driven whale catchers, the catch of blue whales, and baleen whales as a whole, in the Antarctic and sub-Antarctic began to increase dramatically. Between 1930 and 1931, these ships killed 29,400 blue whales in the Antarctic alone. By the end of World War II, populations had been significantly depleted, and, in 1946, the first quotas restricting international trade in whales were introduced, but they were ineffective because of the lack of differentiation between species. Rare species could be hunted on an equal footing with those found in relative abundance.

Blue whale hunting was banned in the 1960s by the International Whaling Commission,[50][51] and illegal whaling by the USSR finally halted in the 1970s,[52] by which time 330,000 blue whales had been killed in the Antarctic, 33,000 in the rest of the Southern Hemisphere, 8,200 in the North Pacific, and 7,000 in the North Atlantic. The largest original population, in the Antarctic, had been reduced to 0.15% of their initial numbers.[10]

Population and distribution today

 
A blue whale set against the backdrop of the Azores
 
Image of a blue whale's tail fluke with the Santa Barbara Channel Islands in the background, August 2007

Since the introduction of the whaling ban, studies have failed to ascertain whether the conservation reliant global blue whale population is increasing or remaining stable. In the Antarctic, best estimates show a significant increase at 7.3% per year since the end of illegal Soviet whaling, but numbers remain at under 1% of their original levels.[10] It has also been suggested that Icelandic and Californian populations are increasing but these increases are not statistically significant. The total world population was estimated to be between 5,000 and 12,000 in 2002, although there are high levels of uncertainty in available estimates for many areas.[8]

The IUCN Red List counts the blue whale as "endangered" as it has since the list's inception. In the United States, the National Marine Fisheries Service lists them as endangered under the Endangered Species Act.[53] The largest known concentration, consisting of about 2,000 individuals, is the North-East Pacific population of the Northern blue whale (B. m. musculus) subspecies that ranges from Alaska to Costa Rica but is most commonly seen from California in summer. Infrequently, this population visits the North-West Pacific between Kamchatka and the northern tip of Japan.

In the North Atlantic, two stocks of B. m. musculus are recognized. The first is found off Greenland, Newfoundland, Nova Scotia and the Gulf of Saint Lawrence. This group is estimated to total about 500. The second, more easterly group is spotted from the Azores in spring to Iceland in July and August; it is presumed that the whales follow the Mid-Atlantic Ridge between the two volcanic islands. Beyond Iceland, blue whales have been spotted as far north as Spitsbergen and Jan Mayen, though such sightings are rare. Scientists do not know where these whales spend their winters. The total North Atlantic population is estimated to be between 600 and 1,500.

In the Southern Hemisphere, there appear to be two distinct subspecies, B. m. intermedia, the Antarctic blue whale, and the little-studied pygmy blue whale, B. m. brevicauda, found in Indian Ocean waters. The most recent surveys (midpoint 1998) provided an estimate of 2,280 blue whales in the Antarctic.[54], of which fewer than 1% are likely to be pygmy blue whales[55] Estimates from a 1996 survey were that 424 pygmy blue whales were in a small area south of Madagascar alone,[56] thus it is likely that numbers in the entire Indian Ocean are in the thousands. If this is true, the global numbers would be much higher than estimates predict.[9]

A fourth subspecies, B. m. indica, was identified by Blyth in 1859 in the northern Indian Ocean, but difficulties in identifying distinguishing features for this subspecies led to it being used a synonym for B. m. brevicauda, the pygmy blue whale. Records for Soviet catches seem to indicate that the female adult size is closer to that of the Pygmy Blue than B. m. musculus, although the populations of B. m. indica and B. m. brevicauda appear to be discrete, and the breeding seasons differ by almost six months.[57]

Migratory patterns of these subspecies are not well known. For example, pygmy blue whales have been recorded in the northern Indian Ocean (Oman, Maldives, Sri Lanka), where they may form a distinct resident population.[57] In addition, the population of blue whales occurring off Chile and Peru may also be a distinct population. Some Antarctic blue whales approach the eastern South Atlantic coast in winter, and occasionally, their vocalizations are heard off Peru, Western Australia, and in the northern Indian Ocean.[57] In Chile, the Cetacean Conservation Center, with support from the Chilean Navy, is undertaking extensive research and conservation work on a recently discovered feeding aggregation of the species off the coast of Chiloe Island in an area named "Golfo del Corcovado", where 326 blue whales were spotted in the summer of 2007.[58]

Efforts to calculate the blue whale population more accurately are supported by marine mammologists at Duke University who maintain the OBIS-SEAMAP (Ocean Biogeographic Information System—Spatial Ecological Analysis of Megavertebrate Populations), a collation of marine mammal sighting data from around 130 sources.[59]

Threats other than hunting

 
A blue whale surfaces off Santa Cruz Island in the Channel Islands, near Santa Barbara, CA

Due to their enormous size, power and speed, adult blue whales have virtually no natural predators. There is, however, one documented case in National Geographic Magazine of a blue whale being attacked by Orcas; although the Orcas were unable to kill the animal outright during their attack, the blue whale sustained massive wounds and probably died as a result of them shortly after the attack.[60]

Blue whales may be wounded, sometimes fatally, after colliding with ocean vessels as well as becoming trapped or entangled in fishing gear.[61] The ever-increasing amount of ocean noise, including sonar, drowns out the vocalizations produced by whales, which may make it harder for them to communicate.[61] Human threats to the potential recovery of blue whale populations also include accumulation of polychlorinated biphenyl (PCB) chemicals within the whale's body.[7]

With global warming causing glaciers and permafrost to melt rapidly and allowing a large amount of fresh water to flow into the oceans, there are concerns that if the amount of fresh water in the oceans reaches a critical point, there will be a disruption in the thermohaline circulation.[senza fonte] Considering the blue whale's migratory patterns are based on ocean temperature, a disruption in this circulation, which moves warm and cold water around the world, would be likely to have an effect on their migration.[62] The whales summer in the cool, high latitudes, where they feed in krill-abundant waters; they winter in warmer, low latitudes, where they mate and give birth.[63]

The change in ocean temperature would also affect the blue whale's food supply. The warming trend and decreased salinity levels would cause a significant shift in krill ___location and abundance.[64]

Museums

 
Blue whale skeleton, outside the Long Marine Laboratory at the University of California, Santa Cruz

The Natural History Museum in London contains a famous mounted skeleton and life-size model of a blue whale, which were both the first of their kind in the world but have since been replicated at the University of California, Santa Cruz. Similarly, the American Museum of Natural History in New York City has a full-size model in its Milstein Family Hall of Ocean Life.

The Aquarium of the Pacific in Long Beach, California features a life-size model of a mother blue whale with her calf suspended from the ceiling of its main hall.[65] The Beaty Biodiversity Museum at University of British Columbia, Canada, is in the final stages of installing a housed display of a blue whale directly on the main campus boulevard.[66] A real skeleton of a blue whale at the Canadian Museum of Nature in Ottawa, Canada was also unveiled in May 2010 [67]

The Museum of Natural History in Gothenburg Sweden contains the only stuffed Blue Whale in the world. There you can also find the skeleton of the whale mounted beside the whale.

Whale-watching

Living blue whales may be encountered on whale-watching cruises in the Gulf of Maine[68] and are the main attractions along the north shore of the Gulf of Saint Lawrence and in the Saint Lawrence estuary.[61]

Footnotes

  1. ^ (EN) D.E. Wilson e D.M. Reeder, Panjabi/Prove, in Mammal Species of the World. A Taxonomic and Geographic Reference, 3ª ed., Johns Hopkins University Press, 2005, ISBN 0-8018-8221-4.
  2. ^ (EN) Taylor, B.L. & Notarbartolo di Sciara, G. (Cetacean Red List Authority) 2008, Panjabi/Prove, su IUCN Red List of Threatened Species, Versione 2020.2, IUCN, 2020.
  3. ^ a b c d e f American Cetacean Society Fact Sheet - Blue Whales, su acsonline.org. URL consultato il 20 June 2007.
  4. ^ Animal Records, su nationalzoo.si.edu, Smithsonian National Zoological Park. URL consultato il 29 maggio 2007.
  5. ^ What is the biggest animal ever to exist on Earth?, su science.howstuffworks.com, How Stuff Works. URL consultato il 29 maggio 2007.
  6. ^ FI - Species fact sheets. Fisheries and Aquaculture Department, Food and Agriculture Organization.
  7. ^ a b c Jason de Koning and Geoff Wild, Contaminant analysis of organochlorines in blubber biopsies from blue whales in the St Lawrence, su whale.wheelock.edu, Trent University, 1997. URL consultato il 29 giugno 2007.
  8. ^ a b c d Assessment and Update Status Report on the Blue Whale Balaenoptera musculus (PDF), su sararegistry.gc.ca, Committee on the Status of Endangered Wildlife in Canada, 2002. URL consultato il 19 aprile 2007.
  9. ^ a b Alex Kirby, Science seeks clues to pygmy whale, in BBC News, 19 giugno 2003. URL consultato il April 21, 2006.
  10. ^ a b c T.A. Branch, K. Matsuoka and T. Miyashita, Evidence for increases in Antarctic blue whales based on Bayesian modelling, in Marine Mammal Science, vol. 20, 2004, pp. 726–754, DOI:10.1111/j.1748-7692.2004.tb01190.x.
  11. ^ Barnes LG, McLeod SA., The fossil record and phyletic relationships of gray whales., in Jones ML et al. (a cura di), The Gray Whale, Orlando, Florida, Academic Press, 1984, pp. 3–32, ISBN 0123891809.
  12. ^ a b Errore nelle note: Errore nell'uso del marcatore <ref>: non è stato indicato alcun testo per il marcatore msw3
  13. ^ Arnason, U., Gullberg A. & Widegren, B., Cetacean mitochondrial DNA control region: sequences of all extant baleen whales and two sperm whale species, in Molecular Biology and Evolution, vol. 10, n. 5, September 1, 1993, pp. 960–970. URL consultato il 25 gennaio 2009.
  14. ^ Sasaki, T, Mitochondrial Phylogenetics and Evolution of Mysticete Whales, in Systematic Biology, vol. 54, n. 1, February 23, 2005, pp. 77–90, DOI:10.1080/10635150590905939. URL consultato il 25 gennaio 2009.
  15. ^ A. Arnason and A. Gullberg, Comparison between the complete mtDNA sequences of the blue and fin whale, two species that can hybridize in nature, in Journal of Molecular Ecology, vol. 37, 1993, pp. 312–322.
  16. ^ Amazing Whale Facts Archive. Whale Center of New England (WCNE). Retrieved on 2008-02-27.
  17. ^ D.P. Simpson, Cassell's Latin Dictionary, 5ª ed., London, Cassell Ltd., 1979, p. 883, ISBN 0-304-52257-0.
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