blue whale
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blue whale |
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| ( Linnaeus , 1758) |
The blue whale ( Balaenoptera musculus ) is a baleen whale in the family of furrow whales (Balaenopteridae). With a body length of up to 33 meters and a body mass of up to 200 tons , the blue whale is the heaviest known animal in the history of the earth . As a cosmopolitan this is kind in all the oceans of the earth spread .
features
anatomy
Blue whales are on average 26 meters long, whereby the specimens living in the waters of the southern hemisphere are usually larger than their counterparts in the northern hemisphere . Individual animals often reach a length of 30 meters, and the largest scientifically measured blue whale was 33.6 meters (1922). This may make the blue whale not only the heaviest but also the longest animal that has ever lived. Few dinosaurs, such as B. the Seismosaurus , were possibly even longer.
Blue whales exhibit a sexual dimorphism in size: females are on average up to six percent larger and can weigh up to 200 tons after the end of the feeding season. The heart of the blue whale weighs on average about 600 kg to a ton, the aorta (the main artery) has a diameter of about 20 cm. The normal heart rate is two to eight beats per minute when descending, but up to 37 times after ascending. The volume expelled by the heart is between 2000 and 5000 liters per minute. The total volume of the blood is 7000-7500 liters.
The blue whale has a streamlined and slender body that is dark blue-gray in color. It is also speckled with lighter spots all over the body. The slightly lighter belly side can also be yellowish in color in animals that have lived in polar waters for a long time. This is due to a vegetation with the harmless diatom Cocconeis ceticola ; Whales with this color are called sulfur bellies. The fin (dorsal fin) is comparatively small with a maximum height of 45 centimeters, it is located on the rearmost quarter of the back. The caudal fin, also known as the fluke , is very broad and notched in the middle. The flippers (pectoral fins), which are pale blue on the underside , are very narrow and have a length that corresponds to about 14 percent of the total length of the animal.
Compared to other furrowed whales, the head of the blue whale is very broad with a very flat snout (rostrum). A web runs from the tip of the snout to the blowhole; the blowhole itself, consisting of two nostrils, is surrounded in front and on the sides by a fleshy wall. There are hairs in different parts of the head, especially on the chin, on both sides of the lower jaw and on the top. A blue whale has 300 to 400 whales in its mouth on each side , colored black and 50 to 100 centimeters long. They have very coarse, species-typical fringes. On the underside there are 50 to 90, according to other sources up to 120, ventral furrows from the mouth to the navel, which represent the eponymous feature of the furrow whales and allow the mouth to expand when eating.
In 1966 the dwarf blue whale ( B. m. Brevicauda ) was described as a subspecies of the blue whale. It should reach a maximum length of 24 meters, as the body section behind the dorsal fin is shorter. The beards are also smaller. However, some zoologists question the validity of this subspecies and consider the specimens to be juveniles, but the increased number of caudal vertebrae of these animals speaks against this view.
genetics
Karyotype
There are different studies to determine the chromosome number of the blue whale with different results. In 1955 it was found on preserved reproductive tissue that blue whales have 2n = 48 chromosomes (i.e. two sets of 24 each). In 1974 the number was also determined on various other whales, including the fin whale , the sei whale and the gray whale , all of which, like the blue whale, have 2n = 44 chromosomes.
DNA
Research on mitochondrial DNA has shown that fin whales and blue whales are able to produce hybrids , although the lines of evolution of the two species have been separate for at least five million years. Female hybrids can even be fertile. The similarities in the karyotype help reduce incompatibilities in meiosis and increase the likelihood of fertility.
Life expectancy
The effective life expectancy of the blue whale is difficult to determine. After investigations of hunted or stranded animals, an achievable age of approx. 100 years can be regarded as certain. However, it is difficult to say how old these animals could have lived had they died of natural causes.
In 2007, scientist Jeffrey Bada from the Scripps Institute for Oceanography in La Jolla , California , was able to determine the age of a harpooned bowhead whale to be 211 years based on the eyeballs of killed whales . This finding suggests that the much larger blue whale can reach an age of at least a similar age, since there is an allometric relationship between body mass and life expectancy in mammals and birds .
distribution and habitat
The blue whale occurs in all of the world's oceans, migrating between polar and moderate latitudes in an annual rhythm. It spends the winter in the temperate and subtropical seas, such as in the area around the Azores , in which its breeding areas are also located; he spends the summer in polar waters where he finds plenty of food. Due to the time lag from north winter to south winter, the following applies: Southern hemisphere whales are closer to the equator in waters when northern hemisphere whales are in the vicinity of the North Pole; conversely, when the northern hemisphere whales are in temperate latitudes, the southern hemisphere whales are near the south pole. The migration routes and the feeding grounds of the whales are very constant, but the specific breeding areas are largely unknown.
As an ocean dweller, the blue whale rarely comes to the coastal areas. However, in the polar waters it follows the receding ice, at the edges of which the largest numbers of krill crabs live. For this reason, blue whales are regularly trapped in the ice when the weather changes suddenly. This is reported regularly, especially from the St. Lawrence River in Canada .
The minke blue whale is found mainly in the southern hemisphere and in the northern Indian Ocean . A large group apparently lives permanently in the sub-Antarctic , other groups have been spotted off Sri Lanka , Chile and the Kerguelen .
Way of life
The evolution of the body size of blue whales was traced back in a specialist publication in 2018 to the fact that their early ancestors - originally much smaller and warm-blooded, land-living mammals - had to compensate for the significantly greater heat loss in the water during the transition to a permanently aquatic way of life. Since heat production ultimately depends on the number of body cells, larger animals can produce and store more heat than small ones. The increase in size is limited by the available food, which is particularly abundant in the sea for blue whales.
nutrition
Like all baleen whales , the blue whale feeding on plankton , which he using its baleen filters out the seawater. Despite its rather coarse bristled Barten he preferred in this small crabs in the centimeter or millimeter range and specializes in the Antarctic to the Antarctic krill . It is thus in direct food competition with other baleen whales, especially the sei and fin whales and the northern and southern minke whales . He is one of the whales that visit the feeding grounds first and hunt closest to the edge of the ice. In addition to krill, it also uses larger schools of copepods and, in rare cases, schools of fish as a source of food. His foraging usually takes him to a depth of about 100 meters.
In the summer months, a blue whale eats an estimated 40 million small crabs per day with a total weight of three and a half tons. The main part of the stomach alone holds a ton of crabs. In the winter months he does not eat at all and lives on his fat reserves.
Locomotion
The blue whale can be recognized on the high seas by its very high blow , i.e. the condensing fountain of air that occurs when you exhale. This can reach heights of nine meters. Normally the animal appears every two minutes, but after long dives the breathing rate increases to up to six breaths per minute. The longest dives reach times of over 20 minutes, but they are usually significantly shorter with an average of three to ten minutes. The caudal fin is seldom lifted out of the water when diving, the fin is hardly visible due to its small size.
The swimming speeds when eating are between 2 and 6.5 km / h, when the animals migrate it can increase to 5 to 33 km / h and maximum speeds of 48 km / h.
A specialist article published in 2016 described the behavior of a minke blue whale off the coast of Western Australia in more detail using GPS data. Accordingly, the examined animal showed different behavioral patterns during its dives. In search of food it dived to a maximum depth of 506 m. In terms of food intake, a distinction was made between deep dives, which on average led to a depth of 338 m, and shallow dives, in which the blue whale was only 16 m below the water surface. When migrating, the whale moved an average of only 13 m under water, which is below the assumed diving depth of 12 m, under which swell has a significant influence on the flow resistance, and dived for about 5.2 minutes each time. The mean speed of the whale over the observed period was only 2.8 km / h, and in 94% of the investigated time it stayed at a depth of less than 24 m, which according to the authors represents a danger as this is the case maximum draft of container cargo ships in Chinamax dimension is.
Social behavior
Blue whales occur mainly as single animals or as mother-child groups, larger group formations are the exception for them and can be traced back to accidental accumulations in the nutritional reasons. There is no social bond within this collection. There are no larger groups on the hikes either; adult animals occasionally lead their young. Pregnant females are the first to migrate to the feeding areas in spring and the last to leave them.
Communication among blue whales is not very pronounced. Stanza- like whale songs like those of the humpback whales are not found in them. The sound repertoire ranges from low-frequency moaning sounds to throbbing, rasping and humming and also includes the occasional ultra-frequent clicks. It is not known whether tail flapping and jumping are also used for communication.
Sound recordings of blue whales:
Reproduction and development
Blue whales are likely to reach sexual maturity between five and six years of age, with a length of 22 meters for males and 24 meters for females. Minke blue whales are sexually mature at a length of 19 meters.
The mating behavior of blue whales is largely unknown; it is likely that they are mating occasionally in the breeding waters. The blue whale calf is born after a gestation period of about eleven months with a length of about seven meters and a weight of about 2.5 tons. Before giving birth, the female migrates to warm, temperate to subtropical waters. The calf is suckled for six to seven months and weaned as it migrates to the feeding grounds, when it is approximately 12.8 meters in length.
A female is pregnant about every two years. In the case of the minke blue whales, it is also assumed that there are two mating seasons in the course of the year, with a main mating time in winter and a secondary mating time in summer. Diseases and parasites are considered to be natural causes of death, as well as attacks by great sharks and the killer whale on young animals and weakened and wounded adults.
Systematics
Robert Sibbald described the blue whale for the first time in 1692 in his Phalainologia nova sive observationes de rarioribus quibusdam balænis in Scotiæ littus nuper ejectis ... , the official first description was in 1758 by Carl von Linné under the scientific name Balaena musculus in the 10th edition of the Systema naturae .
The blue whale is one of eight known species of furrow whales within the genus Balaenoptera , whereby molecular biological studies show a closer relationship of the blue whales to the humpback whales and the gray whales than to other representatives of the genus. On the other hand, there are currently eleven documented cases of blue whale / fin whale crossbreeding in the wild. A separation of the Balaenopteridae from other Waltaxa is assumed for the middle Oligocene , no data are given for the species separation within the taxon .
Within the blue whale, the named two subspecies are assumed, the blue whale Balaenoptera musculus musculus and the dwarf blue whale Balaenoptera musculus brevicauda . In addition, there may be a subspecies called Balaenoptera musculus intermedia , which is said to include the population of the southern oceans; However, this is largely rejected and could not be confirmed even after genetic analyzes.
Whaling and Protection
While the hunt for blue whales was too difficult in earlier centuries because of the size and speed of the animals, they were hunted regularly from the middle of the 19th century . This was mainly due to the development of the harpoon cannon , a harpoon that is fired by means of a kind of cannon and carries an explosive device at its tip. They were, like all other great whales also mainly used as meat and fat suppliers, also the bones (were whalebone ) and the baleen ( whalebone ) used as materials. In the 20th century, about 350,000 blue whales were killed. After 1930, the number of catches fell steadily, as there were hardly any blue whales left, but it wasn't until 1972 that international protection regulations came into force. These are still adhered to internationally today.
Around 1920, the world population of blue whales was estimated at over 220,000 animals, around 90% of them in the southern seas. 40 years later there were only 1,000–3,000 animals. Today the total population is estimated to be around 10,000–20,000 individuals, of which around 6,000 are minke blue whales. It is difficult to precisely record the stocks.
literature
- SG Brown: Balaenoptera musculus (Linnaeus 1758) - blue whale , in Jochen Niethammer, Franz Krapp (ed.): Handbook of Mammals in Europe. Volume 6: Marine mammals, part I whales and dolphins - Cetacea, part IB: Ziphidae, Kogiidae, Physeteridae, Balaenidae, Balaenopteridae. Aula-Verlag Wiesbaden 1995, ISBN 3-89104-560-3 .
- Mark Carwardine: Whales and Dolphins in European Waters . Delius Klasing Bielefeld 2003, ISBN 3-7688-1456-4
- Ralf Kiefner: Whales & Dolphins worldwide. Pacific Ocean, Indian Ocean, Red Sea, Atlantic Ocean, Caribbean, Arctic, Antarctica . Jahr-Top-Special-Verlag, Hamburg 2002, ISBN 3-86132-620-5
- RR Reeves, BS Stewart, PJ Clapham, JA Powell: Sea Mammals of the World. A Complete Guide to Whales, Dolphins, Seals, Sea Lions and Sea Cows. Black, London 2002, ISBN 0-7136-6334-0 (guide with numerous pictures).
- Maurizio Würtz, Nadio Repetto:: Wale & Delphine. Biography of the marine mammals . Year, Hamburg 1998, ISBN 3-86132-264-1 .
Web links
- Balaenoptera musculus in the endangered Red List species the IUCN 2008. Posted by: SB Reilly u. a., 2008. Retrieved December 31, 2008.
- The dilemma of the blue whales , article at www.spektrum.de
- Life-size banner of a blue whale ( Flash , may slow down the browser)
Individual evidence
- ↑ a b c Brown 1995
- ↑ Der Spiegel 49/2019, p. 102: 4 to 8
- ^ GP Dobson: On being the right size: heart design, mitochondrial efficiency and lifespan potential. In: Clinical and experimental pharmacology & physiology. Volume 30, Number 8, August 2003, pp. 590-597, ISSN 0305-1870 . PMID 12890185 .
- ↑ Grzimeks Tierleben, Kindler Verlag, 1972, Volume 11 "Mammals II", p. 471
- ↑ Urania Tierreich, Urania Verlag, 1992, volume "Säugetiere" p. 260
- ↑ a b Würtz, Repetto 1993
- ↑ BJA Nowosielski-Slepowron, AD Peacock: Chromosome number in the blue, fin and sperm whales. Proceedings of the Royal Society Edinburgh, B 65/1955; 358-368
- ↑ Ú. Árnason: Comparative chromosome studies in Cetacea. Hereditas 77/1974; 1-36
- ↑ a b Árnason, Ú. and Gullberg, A. (1993). Comparison between the complete mtDNA sequences of the blue and the fin whale, two species that can hybridize in nature. Journal of Molecular Evolution , 37 (4): 312-322.
- ^ Bérubé, M. and Aguilar, A. (2006). A new hybrid between a blue whale, Balaenoptera Musculus , and a fin whale, B. Physalus : frequency and implications of hybridization. Marine Mammal Science , 14 (1): 82-98.
- ↑ Sabine Gmeinwieser: Animals: Bowhead whale killed by whalers at the age of 211. In: welt.de . May 25, 2007. Retrieved October 7, 2018 .
- ↑ Andreas Feigenspan: Principles of Physiology. Basic mechanisms and evolutionary strategies. Springer Spectrum, Berlin / Heidelberg 2017, pp. 98-100; see also power laws: Why small animals don't get as old as big ones on science.orf.at.
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^ William Gearty, Craig R. McClain and Jonathan L. Payne: Energetic tradeoffs control the size distribution of aquatic mammals. In: PNAS . Online pre-publication of March 26, 2018, doi: 10.1073 / pnas.1712629115
Sea mammals are huge for a reason. On: sciencemag.org of March 26, 2018 - ↑ Kylie Owen et al .: A week in the life of a pygmy blue whale: migratory dive depth overlaps with large vessel drafts . In: Animal Biotelemetry . tape 4 , no. 17 , 2016, doi : 10.1186 / s40317-016-0109-4 .
- ↑ Full title: Phalainologia nova sive observationes de rarioribus quibusdam balænis in Scotiæ littus nuper ejectis in quibus nuper conspectæ balænæ per genera & species, secundum characteres from ipsa naturâ impressos distribuuntur, quædam nunc primum describuntur; errores etiam tirea descriptas deteguntur, & breves de dentium, spermatis ceti, & ambræ griseæ ortu, naturâ & usu dissertationes traduntur.
- ^ Carl von Linné : Systema naturae. 10th edition, Volume 1, 1758, p. 75 ( digitized version ).
