Blue whale facts for kids
Quick facts for kids Blue whale |
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| Adult blue whale from the eastern Pacific Ocean. | |
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| Size difference between a blue whale and a person. | |
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| Balaenoptera musculus (Linnaeus, 1758)
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The blue whale (Balaenoptera musculus) is a marine mammal of the suborder of baleen whales (called Mysticeti). They grow to be about 30 meters long. The biggest blue whale found was 190 tons and measured 98 feet long. Larger specimens have been measured at 110 feet, but never weighed. This makes blue whales the largest animals ever to be on Earth, even bigger than the largest dinosaurs.
The blue whale eats mostly very tiny creatures, like krill. These inch-long, shrimp-like crustacean swim in swarms. In the Antarctic summer, there are so many of these krill that they turn the waters orange. A blue whale can eat eight to ten tons of krill every day.
The blue whale's body is long and slender. It can be various shades of bluish-grey above and somewhat lighter underneath. There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of small krill.
Blue whales were once abundant around the world. In the nineteenth century, they were hunted almost to extinction by whalers. They were finally protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, located in at least five groups. More recent research into the Pygmy subspecies suggests this may be an underestimate. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000). There remain only much smaller (around 2,000) concentrations in each of the eastern North Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere.
Contents
Description and behaviour
The blue whale has a long tapering body that appears stretched in comparison with the stockier build of other whales. The head is flat, U-shaped and has a prominent ridge running from the blowhole to the top of the upper lip. The front part of the mouth is thick with baleen plates; around 300 plates, each around one metre (3 ft) long, hang from the upper jaw, running 0.5 m (20 in) back into the mouth. Between 70 and 118 grooves (called ventral pleats) run along the throat parallel to the body length. These pleats assist with evacuating water from the mouth after lunge feeding (see feeding below).
The dorsal fin is small; its height averages about 28 centimetres (11 in), and usually ranges between 20 cm (8 in) and 40 cm (16 in), though it can be as small as 8 cm (3.1 in) or as large as 70 cm (28 in). It is visible only briefly during the dive sequence. Located around three-quarters of the way along the length of the body, it varies in shape from one individual to another; some only have a barely perceptible lump, but others may have prominent and falcate (sickle-shaped) dorsals. When surfacing to breathe, the blue whale raises its shoulder and blowhole out of the water to a greater extent than other large whales, such as the fin or sei whales. Observers can use this trait to differentiate between species at sea. Some blue whales in the North Atlantic and North Pacific raise their tail fluke when diving. When breathing, the whale emits a vertical single-column spout, typically 9 metres (30 ft) high, but reaching up to 12 metres (39 ft). Its lung capacity is 5,000 litres (1,300 US gal). Blue whales have twin blowholes shielded by a large splashguard.
The flippers are 3–4 metres (10–13 ft) long. The upper sides are grey with a thin white border; the lower sides are white. The head and tail fluke are generally uniformly grey. The whale's upper parts, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform slate-grey color, but others demonstrate a considerable variation of dark blues, greys and blacks, all tightly mottled.
Blue whales can reach speeds of 50 kilometres per hour (31 mph) over short bursts, usually when interacting with other whales, but 20 kilometres per hour (12 mph) is a more typical traveling speed. Satellite telemetry of Australian pygmy blue whales migrating to Indonesia has shown that they cover between 0.09 and 455.8 kilometers (0.056 and 283.2 miles) per day. When feeding, they slow down to 5 kilometres per hour (3.1 mph).
Blue whales typically swim at a depth of about 13 meters (42.5 feet) when migrating in order to eliminate drag from surface waves. The deepest confirmed dive is 506 meters (1,660 feet).
Blue whales most commonly live alone or with one other individual. It is not known how long traveling pairs stay together. In locations where there is a high concentration of food, as many as 50 blue whales have been seen scattered over a small area. They do not form the large, close-knit groups seen in other baleen species.
Size
The blue whale is the largest animal known to have ever lived. By comparison, one of the largest known dinosaurs of the Mesozoic Era was Argentinosaurus, which is estimated to have weighed up to 90 tonnes (99 short tons), comparable to the average blue whale.
Blue whales are difficult to weigh because of their size. They were never weighed whole, but cut into blocks 0.5–0.6 meters (1.6–2 ft) across and weighed by parts. This caused a considerable loss of blood and body fluids, estimated to be about 6% of the total weight. As a whole, blue whales from the Northern Atlantic and Pacific are smaller on average than those from Antarctic waters. Adult weights typically range from 50–150 tonnes (55–165 short tons). There is some uncertainty about the biggest blue whale ever found, as most data came from blue whales killed in Antarctic waters during the first half of the twentieth century, which were collected by whalers not well-versed in standard zoological measurement techniques. The standard measuring technique is to measure in a straight line from the upper jaw to the notch in the tail flukes. This came about because the edges of the tail flukes were typically cut off, and the lower jaw often falls open upon death. Many of the larger whales in the whaling records (especially those over 100 ft (30.5 m)) were probably measured incorrectly or even deliberately exaggerated. The heaviest weight ever reported was 173 metric tons (191 short tons), for a southern hemisphere female in 1947, although it is likely that the largest blue whales would have weighed over 200 short tons (181 t). The longest whales ever recorded were two females measuring 33.6 and 33.3 metres (110 and 109 ft), although in neither of these cases was the piecemeal weight gathered. Possibly the largest recorded male was killed near the South Shetland Islands in 1926 and was measured at 31.7 m (104 ft).
Females are generally a few feet longer than males. However, males may be slightly heavier on average than females of the same length, owing to heavier muscles and bones. Verified measurements rarely exceed 28 meters (92 ft). The longest measured by Macintosh and Wheeler (1929) was a female 28.5 m (93.5 ft), while the largest male was 26.45 m (87 ft), although one of the same authors later found a male of 26.65 m (87.5 ft) and stated that those lengths may be exceeded. The longest whale measured by scientists was 29.9 metres (98 ft) long. Lieut. Quentin R. Walsh, USCG, while acting as whaling inspector of the factory ship Ulysses, verified the measurement of a 29.9 m (98 ft) pregnant blue whale caught in the Antarctic in the 1937–38 season. A 26.8 m (88 ft) male was verified by Japanese scientists in the 1947–48 whaling season. The longest reported in the North Pacific was a 27.1 metres (89 ft) female taken by Japanese whalers in 1959, and the longest reported in the North Atlantic was a 28 metres (92 ft) female caught in the Davis Strait. The average weight of the longest scientifically verified specimens (29.9 m, 98 ft) would be calculated to be 176.5 tonnes (194.5 tons), varying from 141 tonnes (155.5 tons) to 211.5 tonnes (233.5 tons) depending on fat condition. One study found that a hypothetical 33 meter (108 foot) blue whale would be too large to exist in real life, due to metabolic and energy constraints.
Due to its large size, several organs of the blue whale are the largest in the animal kingdom. A blue whale's tongue weighs around 2.7 tonnes (3.0 short tons) and, when fully expanded, its mouth is large enough to hold up to 90 tonnes (99 short tons) of food and water. 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. The heart of an average sized blue whale weighs 400 pounds (180 kg) and is the largest known in any animal. During the first seven months of its life, a blue whale calf drinks approximately 380 litres (100 US gal) of milk every day. Blue whale calves gain weight quickly, as much as 90 kilograms (200 lb) every 24 hours. Even at birth, they weigh up to 2,700 kilograms (6,000 lb)—the same as a fully grown hippopotamus. Blue whales have proportionally small brains, only about 6.92 kilograms (15.26 lb), about 0.007% of its body weight, although with a highly convoluted cerebral cortex.
Feeding
Blue whales feed almost exclusively on krill, though they also take small numbers of copepods. 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; in the North Pacific, Euphausia pacifica, Thysanoessa inermis, Thysanoessa longipes, Thysanoessa spinifera, Nyctiphanes symplex and Nematoscelis megalops; and in the Southern Hemisphere, Euphausia superba, Euphausia crystallorophias, Euphausia valentini, and Nyctiphanes australis.
An adult blue whale can eat up to 40 million krill in a day. The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms (7,900 lb) of krill in a single day. The daily energy requirement of an adult blue whale is in the region of 1.5 million kilocalories (6.3 GJ). Their feeding habits are seasonal. Blue whales gorge on krill in the rich waters of the Antarctic before migrating to their breeding grounds in the warmer, less-rich waters nearer the equator. The blue whale can take in up to 90 times as much energy as it expends, allowing it to build up considerable energy reserves.
Because krill move, blue whales typically feed at depths of more than 100 metres (330 ft) during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 21 minutes are possible. 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.
Life history
Mating starts in late autumn and continues to the end of winter. Little is known about mating behaviour or breeding grounds. In the fall, males will follow females for prolonged periods of time. Occasionally, a second male will attempt to displace the first, and the whales will race each other at high speed, ranging from 17 miles per hour (27 km/h) to 20 miles per hour (32 km/h) in New Zealand. This often causes the racing whales to breach, which is rare in blue whales. This racing behavior may even escalate to physical violence between the males. Scientists have observed this behavior in multiple parts of the world, including the Gulf of St. Lawrence in Canada and the South Taranaki Bight in New Zealand.
Females typically give birth once every two to three years at the start of the winter after a gestation period of 10 to 12 months. The calf weighs about 2.5 tonnes (2.8 short tons) and is around 7 metres (23 ft) in length. Blue whale calves drink 380–570 litres (100–150 U.S. gallons) of milk a day. Blue whale milk has an energy content of about 18,300 kJ/kg (4,370 kcal/kg). The calf is weaned after six months, by which time it has doubled in length. The first video of a calf thought to be nursing was made 5 February 2016.
Sexual maturity is typically reached at five to ten years of age. In the Northern Hemisphere, whaling records show that males averaged 20–21 m (66–69 ft) and females 21–23 m (69–75 ft) at sexual maturity, while in the Southern Hemisphere it was 22.6 and 24 m (74 and 79 ft), respectively. In the Northern Hemisphere, as adults, males averaged 24 m (79 ft) and females 25 m (82 ft) with average calculated weights of 90.5 and 101.5 tonnes (100 and 112 tons), respectively. Blue whales in the eastern North Pacific population were found to be on average 0.91 meters (3 ft) shorter, therefore with males averaging 23.3 meters (76 ft) and 80.5 tonnes (88.5 tons) and females 24 meters (79 ft) and 90.5 tonnes (100 tons). Antarctic males averaged 25 m (82 ft) and females 26.2 m (86 ft), averaging 101.5 and 118 tonnes (112 and 130 tons). Pygmy blue whales average 19.2 meters (63 feet) at sexual maturity, with males averaging 21 meters and females 22 meters (69 and 72 feet) when fully grown, averaging 76 and 90 tonnes (83.5 and 99 tons).
In the eastern North Pacific, photogrammetric studies have shown sexually mature (but not necessarily fully grown) blue whales today average 21.7 m (71 ft), and about 65.5 tonnes (72 tons) with the largest found being about 24.5 m (80.5 ft) – although a 26.5 m (87 ft) female washed ashore near Pescadero, California in 1979.
The weight of individual blue whales varies significantly according to fat condition. Antarctic blue whales gain 50% of their lean body weight in the summer feeding season, i.e. a blue whale entering the Antarctic weighing 100 tons would leave weighing 150 tons. Pregnant females probably gain 60–65%. The fattened weight is 120% the average weight and the lean weight is 80%.
Scientists estimate that blue whales can live for at least 80 years, but 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 eastern North Pacific.
The whales' only natural predator is the orca. Studies report that as many as 25% of mature blue whales have scars resulting from orca attacks. The mortality rate of such attacks is unknown.
Strandings
Blue whale strandings are extremely uncommon, and, because of the species' social structure, mass strandings are unheard of. 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 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.
In June 2015, a female blue whale estimated at 12.2 meters (40 feet) and 20 tonnes (22 tons) was stranded on a beach in Maharashtra, India, the first live stranding in the region. Despite efforts by the Albaug forest department and local fisherman, the whale died 10 hours after being stranded. In August 2009, a wounded blue whale was stranded in a bay in Steingrímsfjördur, Iceland. The first rescue attempt failed, as the whale (thought to be over 20 meters long) towed the >20 ton boat back to shore at speeds of up to 7 miles per hour (11 km/h). The whale was towed to sea after 7 hours by a stronger boat. It is unknown whether it survived. In December 2015, a live blue whale thought to be over 20 metres (65 feet) long was rescued from a beach in Chile. Another stranded blue whale, thought to be about 12.2 metres (40 feet) long, was rescued in India in February 2016. Boats were used in all successful cases.
Vocalizations
Estimates made by Cummings and Thompson (1971) suggest the 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. All blue whale groups make calls at a fundamental frequency 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, lasting about two minutes each, reminiscent of the well-known humpback whale songs. As this phenomenon has not been seen in any other populations, researchers believe it may be unique to the B. m. brevicauda (pygmy) subspecies. The loudest sustained noise from a blue whale was at 188 dB.
The purpose of vocalization is unknown. Richardson et al. (1995) discuss six possible reasons:
- Maintenance of inter-individual distance
- Species and individual recognition
- Contextual information transmission (for example feeding, alarm, courtship)
- Maintenance of social organization (for example contact calls between females and males)
- Location of topographic features
- Location of prey resources
Images for kids
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A blue whale skull measuring 5.8 meters (19 ft)
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The blow of a blue whale
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The small dorsal fin of this blue whale is just visible on the far left.
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Dead blue whale on flensing platform
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