The name Balaenoptera musculus (Linnaeus 1758) was generally used to designate fin whales while B. sibbaldii (Gray 1847) was used for blue whales until True (1899) reassigned the name B. musculus to the blue whale. Musculus means "little mouse" in Latin- possibly evidence of a systematicist with an excellent sense of humor - but is perhaps better explained as a variant of mustoketos (whence mysticetus) or muscular (see Rice 1998).
There are four proposed subspecies (the first three diagnosable):
Balaenoptera musculus musculus (Linnaeus 1758) refers to Northern Hemisphere blue whales.
Balaenoptera musculus intermedia (Burmeister 1871) is used for Antarctic or "true" blue whales.
Balaenoptera musculus brevicauda (Ichihara 1966) is used for blue whales from the Subantarctic Indian Ocean but may also apply to other populations of smaller blue whales. See Pygmy blue whale section
Balaenoptera musculus indica (Blyth 1859) has been used for northern Indian Ocean blue whales but the distinguishing features are poorly known.
Size, shape and distinctive characteristics
Blue whales are the largest animals to ever live on Earth. Adults in the southern hemisphere measure as much as 30 m long and can weigh 150 tons. Blue whales in the northern hemisphere are smaller but still attain lengths of 27 m. Mature pygmy blue whales may only reach 21 m in length. Females are larger than males by 1-2 m. At birth, blue whales can be 8 m long and weigh 3 tons.
Blue whales are gray-blue in color with unique mottling patterns on their skin that have been used to identify individuals. Their dorsal fin is quite small (~30 cm) and variable in shape. The rostrum is broad and flat with a single ridge that runs from the high splash guard of the blowholes to the tip of the rostrum. Overall the body of a blue whale is streamlined but the ventral grooves (or pleats) allow the mouth to expand such that feeding blue whales resemble giant tadpoles when seen from the air.
Blue whales have as many as 400 plates of baleen on each side of the upper jaw. This baleen is usually black and relatively short (0.5 m).
Blue whales are a cosmopolitan species and are found in all oceans of the world from the ice edge in the Antarctic to tropical waters of equatorial regions. Exceptions include the Mediterranean Sea and the Arctic Ocean (although they are regularly sighted near the ice edge in the North Atlantic. There are few records from the Bering Sea.
Blue whales are generally found in areas of high primary and secondary productivity including areas of open-ocean upwelling (i.e. the Costa Rica Dome in the tropical Pacific). Although it is generally believed that blue whales follow an overall annual migration pattern from high to low latitudes from winter to spring there is mounting evidence that many animals remain at high latitudes during winter months.
Ecology and Behaviour
Blue whales tend to be solitary although large groups can be found in areas a of high productivity such as Monterey Bay, CA the Gulf of St Lawrence, Canada or the Santa Barbara Channel Islands, CA. Blue whales are lunge feeders that rely on large concentrations of krill.
The migratory behavior of blue whales is variable with some populations considered resident (i.e. northern Indian Ocean) while others may undertake seasonal migrations. There is no known wintering area for blue whales although Chiloe, Chile has been proposed as a nursery for southeast Pacific blue whales.
Blue whales produce very loud, long, low frequency sounds that are regionally distinctive leading to the proposal of "acoustic populations" of blue whales. Some of their sounds are thought to be used as contact calls while others, when repeated in long bouts, are considered song. To date, evidence supports only males producing song and therefore it has been proposed to serve similar functions as humpback whale song. In the North and South Pacific, two distinct song types have been identified thus far for each area, three in the Indian Ocean, and one each in the North Atlantic and around the Antarctic. Detection of these acoustic population signatures have been used to document migration routes and population ranges.
Both male and female blue whales are thought to reach sexual maturity between 5-15 years of age. Females give birth every 2-3 years and gestation is 10-11 months followed by weaning of calves after 7 months. During nursing calves grow from 7 m to 16 m.
Estimates of age have been obtained from counts of layers of wax that are thought to be laid down in the external ear canal annually. These have resulted in maximum life span estimates of anywhere from 60-110 years.
Blue whales are lunge feeders that feed primarily on euphausiids (krill) although they are also known to eat red crab larvae (Pleuronectes spp).
There is no current global estimate of abundance for blue whales.
Antarctic blue whales may now number 1700 (CI 860-2900) which is less than 1% of the estimated pre-exploitation population (Branch et al. 2004).
The only population for which there is a good estimate of abundance is the eastern North Pacific stock that is thought to be as large as 3000 (Calambokidis and Barlow 2004).
There may be 1000-2000 blue whales in the central North Atlantic (Pike et al. 2004).
The IUCN status of blue whales globally is endangered with Antarctic blue whales listed as critically endangered. This status is the result of depletion to near extinction by commercial whaling efforts in the early 1900s.
What little data exist seem to suggest that blue whale populations are increasing.
Blue whales have been protected from whaling since 1966 by the International Whaling Commission. Despite this protection, illegal catches continued in the Indian Ocean and North Pacific until 1972. The reduction of Antarctic blue whales to less than 1% of pre-whaling populations may have resulted in a genetic bottleneck although this has not been proven. At present there is no direct threat from whaling but other anthropogenic threats exist. These include noise pollution (masking) from increasing low-frequency noise in the oceans; pollution and ship strikes. Loss of sea ice in the Antarctic due to a warming climate may also impact blue whales by reducing densities of krill (esp. Euphausia superba).
Branch TA, et al. 2004. Evidence for increases in Antarctic blue whales based on Bayesian modelling. Mar Mamm Sci 20:726-754.
Branch TA, et al. 2007. Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean. Mamm Rev 37:116-175.
Calambokidis J et al. 2009. Insights into the population structure of blue whales in the eastern North Pacific from recent sightings and photographic identifications. Mar Mamm Sci 25:816-832.
Calambokidis, J et al. 2008. Insights into the underwater diving, feeding, and calling behavior of blue whales from a suction-cup attached video-imaging tag (CRITTERCAM). Mar Tech Soc J 41:19-29.
Calambokidis, J et al. 1990. Sightings and movements of blue whales off central California 1986-1988 from photo-identification of individuals. Rep Int Whal Commn (Special Issue 12): 343-348.
Croll DA et al. 1998. An integrated approach to the foraging ecology of marine birds and mammals. Deep-sea Res II 45: 1353–1371.
Cummings WC and Thompson PO. 1971. Underwater sounds from the blue whale, Balaenoptera musculus. J Acoust Soc Am 50:1193-1198.
Fiedler PC et al. 1998. Blue whale habitat and prey in the California Channel Islands. Deep-sea Res II 45: 1781–1801.
Gill PC. 2002. A blue whale (Balaenoptera musculus) feeding ground in a southern Australia coastal upwelling zone. J Cet Res Manage 4:179-184.
Gilpatrick JW, and WL Perryman. 2008. Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (Balaenoptera musculus). J Cet Res Manage 10:9-21.
Leduc RG, et al. 2007. Patterns of genetic variation in southern hemisphere blue whales, and the use of assignment test to detect mixing on the feeding grounds. J Cet Res Manage 9:73-80.
McDonald MA, et al. 2006. Biogeographic characterisation of blue whale song worldwide: using song to identify populations. J Cet Res Manage 8:55-65.
Mellinger DK and Clark CW. 2003. Blue whale (Balaenoptera musculus) sounds from the North Atlantic. J Acoust Soc Am 114:1108-1119.
Rice DW. 1998. Marine Mammals of the World: Systematics and Distribution. Special Publication Number 4 of the Society for Marine Mammalogy. Allen Press, Lawrence, KS
Stafford KM, et al. 2001. Geographic and seasonal variation of blue whale calls in the North Pacific. J Cet Res Manage 3:65-76
Yochem PK and Leatherwood S. 1985. Blue whale, Balaenoptera musculus (Linnaeus, 1758). In Ridgeway SH and Harrison RJ (eds.), Handbook of Marine Mammals, Vol. 3: The Sirenians and Baleen Whales. Academic, London, pp. 193-240.