Blue Whale
(Balaenoptera musculus)
Aerial image of a blue whale
Family: Balaenopteridae
Species: Balaenoptera musculus
Length: 20 to 30 m. The biggest specimen was 33.3m, captured in the Southern Ocean.
Weight: 75 to 130 metric tons.
Life expectancy: Confirmed at least 50 years, estimated to reach 70-90 years, with an inferred generation time of 31 years.
Diet: Primarily Krill (euphausiids) and copepods. The St. Lawrence blue whales are known to feed predominantly on Krill species Meganyctiphanes norvegica and Thysanoessa raschii.
Behaviour: Found mainly as solitary individuals or in pairs, and occasionally in small groups. They do, however, aggregate in larger groups in areas of dense prey patches.
Characteristics and Taxonomy
The blue whale (Balaenoptera musculus) is a baleen whale belonging to the family Balaenopteridae, which includes the group of cetaceans known as rorquals. Common names are blue whale, sulfur-bottom, Sibbald’s rorqual, great blue whale, and great northern rorqual. The largest animal known to have existed on Earth, it is found worldwide, ranging into all oceans (Yochem and Leatherwood, 1985). In Quebec, they can be seen in the Saint-Lawrence Estuary from Tadoussac to Pointe des Monts along the North Shore, around Matane on the South shore, and east along the Gaspesian peninsula in the summer and fall. Blue whales enter the St Lawrence through Cabot Strait in late winter / early spring. In fact, some individuals have been observed feeding in the Gulf during winter months. Blue whales als concentrate in Eastern Canadian waters along the southern edge of the Grand Banks and Scotian Shelf to New England.
Three subspecies have been designated: what has been considered the largest, B. musculus intermedia, found in Antarctic waters; B. musculus musculus in the Northern Hemisphere; and B. musculus brevicauda, from the subantarctic zone of the southern Indian Ocean and southwestern Pacific Ocean, also colloquially known as the “pygmy” blue whale.
Southern Hemisphere blue whales are on average larger than those in the Northern Hemisphere. The largest recorded were caught in the Southern Ocean and measured 31.7–33.3 m (104–110ft) long. The largest recorded for the Northern Hemisphere was a 28.1-m (92-ft) female caught in Davis Strait. In the North Pacific females of 26.8 m (88 ft) and 27.1 m (89 ft) have been recorded. Adults generally weigh from 75 to 150 tons, but can reach the size of a 190-ton female taken off South Georgia in 1947.
Blue whales project a tall (10–12 m) spout, denser and broader than that of fin whales, (B. physalus). When surfacing, the blue whale raises its shoulder and blowhole region out of the water more than other rorquals. The prominent fleshy ridge just forward of the blowhole, or “splash guard,” is strikingly large in this species.
Blue whales have a tapered elongated shape, a broad, relatively flat, U-shaped head, adorned by a prominent ridge from the splash-guard to the tip of the rostrum, and massive mandibles. Black, 1m long baleen plates found on each side of the upper jaw, number 270–395. There are 60–88 ventral pleats running longitudinally from the tip of the lower jaw to the navel, which enable the ventral pouch to distend dramatically when feeding.
The dorsal fin, positioned far back on the body, is proportionally smaller than in other balaenopterids and ranges in shape, from a small nubbin to triangular and falcate. The flippers are long and bluntly pointed, slate grey, with a thin white border dorsally and white ventrally; they reach up to 15% of the body length.
Blue whales generally appear paler in colouration than all species of large whale except for the grey whale (E. robustus), which is much smaller. The characteristic mottled pigmentation is a blend of light and dark shades of grey displayed in patches of varying sizes. Underwater the colour is slate blue on overcast days to silvery/turquoise on bright sunny days. The mottling is found along the body dorsoventrally, occasionally on the flippers, but not on the head and tail flukes. Two pigmentation configurations are found in blue whales, one where a darker, dominant background is mottled with sparser pale patches of pigmentation, while in the other there is a predominantly pale background mottled with sparser dark patches. Individual blue whale pigmentation can vary from sparingly mottled, to densely mottled individuals. The mottling is unique to each whale, and is the basis for photo-identification studies. Distinct chevrons curving back from behind the blowholes can be found on some individuals. The tail flukes, are predominantly grey above and below; however, some individuals have white ventral pigmentation patches that are used for individual identification (Sears et al., 1990). A yellow-green to brown cast, caused by the presence of a diatom (Cocconeis ceticola) film, can cover all or part of the body of blue whales found in cold waters. The yellowish, diatom-induced tint is the reason the “sulfur-bottom” moniker was once used for blue whales.
Blue whales used to be abundant around the world, but their population was severely depleted following the nineteenth and early twentieth-century commercial whale hunt, when at least 13,000 specimens were caught in the North Atlantic. The species is very slowly recovering at a global level, however, they remain well below pre-whaling numbers and have been classified as 'Endangered' according to the IUCN (International Union for Conservation of Nature). The North Atlantic population is divided into two geographical subpopulations: Northwest Atlantic (NWA) and Northeast Atlantic (NEA). The Northwest Atlantic population has been added to the list of the Species At Risk Act (SARA) in Canada. MICS' research results indicate that there is very low population recruitment, meaning that the birth rate (measured by calf sightings) has remained quite low. In almost 40 years of blue whale research, only 23 calves have been identified in the NWA.
MICS was the first organization to carry out long-term studies of the endangered blue whale. We have since studied blue whales throughout the St. Lawrence, in the Sea of Cortez, off Iceland, West Greenland and the Azores. We have compiled extensive blue whale photo-identification catalogues for the Northwest and Northeast Atlantic as well as the Sea of Cortez, and MICS is the curator of the North Atlantic catalogues. The Northwest Atlantic catalogue now contains 525 individual whales, while close to 700 have been catalogued for the Northeast Atlantic. New whales are added to the catalogue almost every year, collected directly by MICS staff and through collaborations with other researchers, whale-watchers, and navigators.
Despite having being reduced greatly due to whaling, the blue whale remains a cosmopolitan species separated into populations from the North Atlantic, North Pacific, and Southern Hemisphere. In the North Atlantic, eastern and western subdivisions are recognized. Photo-identification work from eastern Canadian waters indicates that blue whales from the St. Lawrence, Newfoundland, Nova Scotia, New England, and west Greenland all belong to the same population, whereas blue whales photo-identified from Northwest Africa, the Azores, Iceland and Spitsbergen appear to be part of a separate population. The best-known population in the North Atlantic is that found in the St. Lawrence from April to January (Sears et al., 1990). In the eastern North Atlantic (NEA) most blue whale photo-identification effort has been in Icelandic and Azorian waters. NEA photo-IDs have also come from Spitsbergen, Ireland, Jan Mayen, East Greenland, Spain, and NW Africa. It should be noted that considerably less field effort has been carried out in the NEA compared to the NWA.
In the North Atlantic, blue whales reach Davis Strait and Baffin Bay in the west and to the east they travel to Jan Mayen and Spitsbergen, right to the edge of pack ice during summer months. Though blue whale winter distribution in the NWA is not well defined, some have been observed in the St. Lawrence as late as February, while satellite tagging and acoustic studies confirm distribution out across the North Atlantic basin with presence at offshore seamounts, and as far south as Bermuda, the Carolinas and Florida. The southernmost observations in the NEA are off NW Africa and the Cape Verde Islands.
In the North Pacific, acoustic analysis of blue whale vocalizations indicates that there are two populations. The best known is that from the eastern North Pacific where blue whales reach as far north as Alaska but are regularly observed from California in summer, south to Mexican and the Costa Rica Dome waters in winter. Abundance estimates of approximately 3000 animals (CV 5 0.14) by line-transect methods and 2000 by capture–recapture (mark-recapture; photo-identification), have been determined for this extensively studied population (Calambokidis and Barlow, 2004). From the Gulf of California, Mexico (winter/spring), blue whales migrate north (April/June), where a large proportion is found in California waters. From there some reach Canadian waters, and others may disperse north to the Gulf of Alaska. A few blue whales have been reported recently from the western North Pacific, including the Aleutian Islands, Kamchatka, Kurils, and Japan.
Blue whales are also found in the northern Indian Ocean; however, it is not clear whether these form a distinct population. Recent studies off Sri-Lanka have led to the creation of a photo-identification catalogue of at least 100 individuals.
In the Southern Ocean, where the blue whale was historically most abundant, it is very rare today, with an abundance estimate at 1700 (95% confidence interval 860–2900) (Branch et al., 2007). A population of 424 (CV 5 0.42) has been estimated to frequent the Madagascar Plateau in the austral summer (Best et al., 2003). Although the general population structure in the Southern Ocean is not well understood, evidence shows discrete feeding stocks. A feeding and nursing ground has been identified in southern Chile. Consistent with these feeding areas, the International Whaling Commission has assigned six stock areas for blue whales in the Southern Hemisphere.
Estimating the population size throughout the North Atlantic has proven most difficult due to the constraints of following and surveying such a transient species across ocean basins. Based on mark-recapture models, the portion of NWA blue whale population found in the St. Lawrence and throughout eastern Canadian shelf waters, where sighting data has been most consistent, has been estimated at around 150-200 individuals in summer. Their migratory movements are not yet very well understood, but some NWA blue whales travel North as far as Davis Strait and the western shore of Greenland in summer, and South through Cabot Straight, along the US east coast as far south as the Carolinas in winter. Thus far there appears to be only limited exchange between NWA and NEA subpopulations, because we have only discovered two blue whales that were matched to both NWA and NEA catalogues.
Since 2010, MICS has been involved in a satellite tagging project, which aims to discover more detailed information on blue whale dispersal and migration in the NWA. Its most successful tags lasted for months, including the one deployed on B244 “Symphonie”, which transmitted geographical data for 6 months, giving us the first insight into blue whale movements in the Northwest Atlantic during the winter time.
Food availability probably dictates blue whale distribution for most of the year. Although they can be found in coastal waters of the St. Lawrence, Gulf of California, Mexico, and California, they are found predominantly offshore. They appear to feed almost exclusively on euphausiids (krill) worldwide in areas of cold current upwellings. When they locate suitably high concentrations of euphausiids, they feed by lunging and gulping large mouthfuls of prey. The mouth is then almost completely closed and the water is expelled by muscular action of the distended ventral pouch and tongue through the still exposed baleen plates. Once the water is expelled, the prey is swallowed. When they feed just a few meters below the surface, they often surface slowly, belly first, exposing the throat grooves of the ventral pouch. If the prey is close to the surface, blue whales lunge vigorously on their sides or lunge up vertically by projecting their cavernous lower jaws 4–6 m up through the surface. Although surface feeding has often been observed during the day, it is more usual for blue whales to dive to at least 100 m into layers of euphausiid concentrations during daylight hours and rise to feed near the surface in the evening, following the ascent of their prey in the water column. In the North Atlantic, blue whales feed on the krill species Meganyctiphanes norvegica, Thysanoessa raschii, T. inermis, and T. longicaudata; in the North Pacific, Euphausia pacifica, T. inermis, T. longipes, T. spinifera, and Nyctiphanes symplex. In Antarctic waters they prey on E. superba, E. crystallorophias, and E. vallentini.
Longevity is thought to be at least 80–90 years and probably longer and documentation of natural mortality is rare. Long-term photo-identification studies in the St. Lawrence and northeast Pacific, confirms that they live for at least 50 years. The principal predator is the killer whale, Orcinus orca, but there is little evidence of attacks on blue whales in the North Atlantic or Southern Hemisphere. In the Gulf of California, Mexico, however, 25% of the blue whales photo-identified carry rake-like killer whale teeth scars on their tails, indicating that attacks occur with some regularity but are probably rarely successful. In the St. Lawrence, ice entrapment mortality, where animals have been crushed, stranded, or suffocated by current and wind-driven ice floes in the late winter-early spring, has been reported. Increasing anthropogenic noise from shipping and oil exploration may also limit recovery of blue whales.
Ecology
Blue whales are observed most commonly alone or in pairs; however, concentrations of 50 or more can be found spread out in areas of high productivity.
Although not noted for raising their flukes when diving, approximately 18% of blue whales observed in the western North Atlantic and Northeast Pacific do so. Studies off Sri Lanka report that 55% of blue whales there fluke up when diving.
When feeding at depth, blue whales will generally dive for 8–15 min; 20-min dives are not uncommon. The longest dive recorded was of 36 min; however, dives of more than 30 min are rare. Swimming at 3–6 km/h is most common, however, they can attain travel speeds of 7–20 km/h, and when chased by boats, predators, or interacting with other blue whales, they can reach upward of 35 km/h.
Blue whales vocalize regularly throughout the year with peaks from midsummer into winter months. The majority of vocalizations are infrasonic sounds of 17–20 Hz, lower than humans can detect. Their sounds, at 188 decibels are one of the loudest and lowest made by any animal. The calls can be heard easily for hundreds even thousands of kilometres under optimal oceanographic conditions, and may cover whole ocean basins. The low frequencies are ideal for communication between individuals of a widely dispersed and nomadic species through water without much loss of information. Geographic variation, seasonality, and diel variation in the sounds have been studied intensively in recent years (Stafford et al., 2004, 2005) and are useful in delineating populations.
Little is known of mating behaviour in blue whales. However, female-male pairings have been noted with regularity in the St. Lawrence from summer into fall, some lasting for as long as 5 weeks. When a female/male pair is approached by a third blue whale-usually a male, vigorous surface displays ensue lasting for 7-50min, where all three animals can be seen racing high out of the water.
Blue whales reach sexual maturity at 8-10 years of age. Length at sexual maturation in females from the Northern Hemisphere is 21–23 m and 23–24m in the Southern Hemisphere. Males reach sexual maturity at 20–21m in the Northern Hemisphere and at 22m in the Southern Hemisphere. Mating takes place from late fall and throughout the winter. Females give birth every 2–3 years in winter after a 10-12-month gestation period. The calves, which weigh 2–3 tons and measure 6–7m at birth, are weaned when approximately 16 m long at 6–8 months. No specific breeding ground has been discovered for blue whales in any ocean, although mothers and calves are sighted regularly in the Gulf of California, Mexico, in late winter and spring, while low numbers of mother-calf pairs have been sighted in the Costa Rica Dome region during the same period.
Note: This text includes excerpts of the Encyclopedia of Marine Mammals, from the section on Blue whales, which coauthored by Richard Sears (MICS founder and CEO).
