Dugong
| Dugong | ||||||||||||
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Dugong in the Bay of Marsa Murena , in the Red Sea off Egypt |
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| Systematics | ||||||||||||
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| Scientific name of the genus | ||||||||||||
| Dugong | ||||||||||||
| Lacépède , 1799 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Dugong dugon | ||||||||||||
| ( Statius Müller , 1776) |
The Dugong ( Dugong dugon rare), also dugongidae or Seeschwein called, is the only one still living representative of dugongs (Dugongidae), which together with the manatees or manatees, the order of manatees form (Sirenia). While the manatee species occasionally visit fresh water, the dugong is almost exclusively in salt water. Its current range includes the coasts of the Indian Ocean and parts of the western Pacific . The populations off Australia are significant - the rest are very small.
morphology
The dugong is up to four, usually three meters long and weighs between 230 and 900, usually 400 kilograms, which makes it larger than the Amazon manatee , but remains smaller than the other two species of manatee. Females are slightly larger. The smooth, brown to dark gray skin of the dugong has short whisker hairs at intervals of two to three centimeters. The 35 to 45 centimeter long forefins are used by the young animals for locomotion (propulsion), while adult animals use the so-called flippers almost exclusively for steering and leave the propulsion to the tail fin (fluke). The flippers are also used to "prop up" on the ground when grazing, not to inspect the food as animals did in captivity. Unlike the manatees, the caudal fin is not round, but straight or curved at the rear edge, making the fork-shaped tail a striking distinction between the dugong and manatees. The snout is short and wide and characterized by downwardly curved, movable lower lips and a slit-shaped mouth.
The dugong also differs from the manatees in the structure of its skull : the premaxillary forms a kinked, conspicuous rostrum , flanked by very robust zygomatic arches , which is the attachment surface for the masseter muscle . The nasal bone is missing. The dugong's dentition is characteristic: males form an incisor (I²) that protrudes and forms a tusk when they are nine to ten years old, i.e. during puberty, but in females it remains in the tooth socket. The tooth formula for an adult female is I 0/0 C 0/0 P 0/0 M 2-3 / 2-3. The molars are cylindrical, thick, have no roots and no enamel. The last molar is double-cylindrical. In young animals, two molars are missing per jaw half , which break through late and grow steadily. The young animals also have a few premolars , which, however, move further forward in the jaw with increasing age, where they ultimately disappear due to wear.
The dugong has seven cervical vertebrae (manatees only have six), 18 to 19 thoracic vertebrae (relatively high number), four to five lumbar vertebrae (rather small number), at most one sacral vertebra and 28 to 29 tail vertebrae . The shoulder blade is sickle-shaped; it has a short acromion . The breastbone is reduced, as is the pelvic girdle ; the collarbone is entirely absent, and the pubic bone is absent. The coracoid is well developed. The carpal bones show a tendency to fuse in the dugong.
Occurrence
The current range of the Dugong includes the coasts of 40 to 48 countries, depending on the source, stretching from East Africa to Vanuatu . To the north and south, its range is limited by the 26th north and 27th south latitude. Only in Australian coastal waters there are larger contiguous populations (especially in Shark Bay ); in the rest of the distribution area there are small, threatened populations separated by large areas. In most of the range, dugongs are mainly known from few sightings, stories from seafarers or from found drowned animals. In historical times, dugongs were roughly common in all seagrass - covered Indo-Pacific waters. They may have been known to the ancient Egyptians from the Red Sea. Every now and then a few dugongs are found in the Mediterranean , whereby these animals have entered the Mediterranean through the artificial Suez Canal . Like most manatees, the dugong also lives in rather shallow coastal waters, which are usually quite cloudy.
Way of life
General
Not much is known about the way of life of the dugongs, as, among other things, they often live in murky waters, are shy and flee whenever they are disturbed. Since only the top of the head and nostrils are lifted out of the water when breathing, they are not easy to see. However, when the water is very clear, a dugong often swims over 100 meters away from seemingly harmless divers or ships in order to examine them. Occasionally there are animals that seek direct contact with divers and play with them for hours. After the curiosity has been satisfied, the dugong zigzags away, probably in order to be able to keep an eye on the object being examined with one eye at a time. The curiosity of the dugongs suggests that they have few natural enemies, especially as adults, although it is reported that even large dugongs have been attacked by killer whales and sharks . In addition to their size, dugongs are also protected by robust skin, dense bone structure and more coagulable blood that quickly closes wounds. In addition, dugongs have already been observed in shallow water, which together pushed a shark with their snouts and thus escaped an enemy in cooperation - a highly developed social behavior.
Dugongs can move at about 10 km / h, in a hurry about twice as fast. The animals breathe every 40 to 400 seconds while grazing. The length of the breathing interval increases with increasing depth. Sometimes they look around while breathing; but mostly only the nostrils protrude from the water. Often when they exhale they utter a sound that could be onomatopoeically expressed as “p-haa” and that can be heard quite far.
Migratory behavior
Animals marked with transponders have shown that dugongs are essentially sedentary animals whose roaming areas are only a few dozen square kilometers in size. Occasionally, however, dugongs go on sudden hikes of hundreds of kilometers, the reasons for which are not yet fully understood.
Migratory behavior was researched in Australia, where 60 animals were monitored with transponders and satellites . The movements depend on the tides , and in areas with a pronounced tidal range the animals move frequently, as they usually graze at a depth of two to six meters and a minimum of one meter is required. Dugongs move little in places with little tidal range, as well as where the seagrass grows outside the intertidal zone.
Especially in the northern parts of their distribution area in Australia, dugongs migrate annually to warmer winter waters. In Shark Bay , Western Australia , the dugongs there are forced in winter by the low temperatures to leave their summer grazing grounds and thus their preferred source of food and, after a hike of 160 kilometers, to reach the western, winter-warm part of the bay, where they can remove the leaves of the hard-stemmed, shrubby seagrass Amphibolis antarctica . In Moreton Bay , the dugongs make “round trips” of 15 to 40 kilometers between their pastures and the open sea. The migrations of some animals around the Great Barrier Reef and the Gulf of Carpentaria are less well explained : They cover 100 to 600 kilometers in a few days (counting the way there and back). An attempt to explain the hikes is based on the examination of the seagrass meadows, as these often disappear shortly after their formation or after storms.
Social behavior
Occasionally, dugongs form large herds of several hundred animals, but most animals live in smaller groups of a maximum of twelve animals, which include one or more females and their calves. Numerous dugongs are loners. 60 to 100 animals often gather in very productive areas with seagrass. They communicate, among other things, by twittering, trilling and whistling. Through these sounds, conspecifics are warned of dangers or contact is maintained between the calf and mother. Empathy with dugongs was observed by Ernst Christoph Barchewitz , when a female was caught and killed, the male also had himself killed.
nutrition
Dugongs are purely herbivorous (herbivorous) and feed on seaweed. They mainly eat the carbohydrate-rich rhizomes of the seagrass, which are rooted out of the soil substrate; however, they do not only feed on the subterranean parts of the plants, which are often devoured whole. They often graze at depths of two to six meters. However, the typical shallow, winding furrows or gullies that they leave when grazing were also found at a depth of 23 meters. To get to the rhizomes or roots, dugongs have developed special techniques. The rhizomes are dug up. Dugongs reach roots in the following sequence of movements: The uppermost layer of sediment is removed with lateral muscle contractions of the horseshoe-shaped upper lips, then the roots are loosened from the soil, cleaned by shaking and eaten. The seaweeds preferred by dugongs are small, delicate and often come from the genera Halophila and Halodule . Although they contain only a small amount of fiber , they contain numerous, easily digestible nutrients .
It is interesting that the seagrass beds often heavily on dugongs affected are; Seagrass areas often grazed by dugongs show over time more and more low-fiber , higher -nitrogen plants. If a seagrass meadow is not used by dugongs, the proportion of fiber-rich species increases again.
Reproduction
The tropical climate enables long mating seasons, which in the case of the Dugong extend to four to five months. In one area the males always met at an advertising space; this is probably the same in other areas as well. The males emit lure calls. Senior males perform movements comparable to land sit-ups . This makes the dugong the only marine mammal that exhibits classic advertising behavior.
After a gestation period of about 13 months, the females go to shallow water to give birth. After that, the almost always single, 100 to 120 centimeter long and 20 to 35 kilogram heavy calf stays close to the mother for about two years (at least 18 months) and looks for cover behind its back if there is danger. However, young manatees begin to eat seaweed on their own shortly after birth. For the first time, cows give birth when they are ten to 17 years old. Sometimes females who suckle a young are pregnant before the young are weaned, with an average of three to seven years between two births.
Dugongs are likely to live to be over 60 years old. The oldest known female dugong was estimated to be 73 years old after her death based on the growth of her tusks.
Systematics
The dugong is the only representative of the monotypical family of fork tailed manatees (Dugongidae) still alive today . In historical times there was another, gigantic representative of the fork-tailed manatee with Steller's manatee , but this species died out in 1768 due to hunting.
Dugongs and people
Dugongs belong to the endangered species mainly because of their hunting. Newer threats arise from pollution, the destruction of ecosystems and collisions with ships. Six dugongs are currently (April 2014) kept in human care in underwater parks and aquariums in Japan, Singapore, Indonesia and Australia.
etymology
The name comes from a Malayo-Polynesian language (cf. Malay duyung ). Georges-Louis Leclerc de Buffon introduced it to zoology in 1765 , here still in the form of dugon . Buffon again referred to a travel report by Ernst Christoph Barchewitz published in 1751 , according to which the animal on the island of Lethi was called dugung . Buffon identifies this island with the Philippine island of Leyte ; however, there is probably a mix-up here, because Barchewitz was stationed as an officer of the Dutch East India Company not on Leyte, but rather on the " southwest island " Leti near Timor . The form dugong in use today is first found in 1788 by Johann Friedrich Gmelin .
The dugong as a hunting object
The dugong was hunted by the indigenous people of Australia and other areas, but later "western" hunters were also involved. Around 1,000 dugongs were shot annually on Torres Street. Today the dugongs are no longer often hunted, sometimes hunting them is a criminal offense.
Most of the time, the dugong was hunted for its food, which is said to resemble soft veal. High quality leather can be made from the hide. Oil is also extracted from the animals, a total of 24 to 56 liters per adult specimen, which is used as lubricating oil etc. In addition, bones and teeth are used, from which jewelry, sculptures and other things are made. It can also be used to produce high-quality coal for sugar refinement. Asian cultures caught the dugong to make "medicine" and aphrodisiacs .
More threats
Seagrass meadows are very sensitive ecosystems and are currently not only threatened by bottom trawls , but also by sewage, environmental toxins, heavy metals and waste. Storms can also destroy hundreds of square kilometers of seagrass meadows, which, however, regenerate quickly if the environmental conditions remain unchanged. Loss of food and habitat is one of the threats to the dugong. They are also damaged and poisoned by chemicals. Between 1996 and 2000, a total of 53 dugongs stranded dead on the Queensland coast were examined . In 59% of the animals, DDT could be detected in the blubber .
Fishing nets (especially trawls ) are perhaps one of the greatest threats to dugongs today. The animals get caught in the nets and drown. In the meantime, sound-based warning systems have been developed for dugongs, which can significantly reduce mortality . Between 1962 and 1995, 837 dugongs were caught in shark nets to protect beach tourists, the majority of which died.
Collisions with ships are also a threat to the dugongs. Ship propellers often fatally injure the animals. Dugongs in shallower waters are particularly affected.
Inventory development
The dugong is now threatened in many places by hunting and other dangers ; they have now completely disappeared from the Mascarene , the Laccadives and the Maldives . They have become very rare off Guam , Yap , the Ryūkyū Islands and the coasts of East Asia. In general, the populations around India, Africa, Madagascar and Southeast Asia are severely threatened. In 1979 the total was estimated at 30,000 individuals in the wild, but aerial surveillance from 1994 came to much higher results: About 10,000 animals live in Shark Bay, 12,000 around the Great Barrier Reef, 17,000 in the Gulf of Carpentaria, at least 14,000 in the rest of the Northern Territory from Australia and at least 24,000 on Torres Strait. In total there are around 80,000 animals around Australia. This is the only area where dugongs are still common. The largest population outside of Australia is in the Persian Gulf; it includes more than 7000 animals.
Dugongs in literature
During his stay on Leti Island as a commanding officer from 1714 to 1720 , the Erfurt East India traveler and author Ernst Christoph Barchewitz reported on the mourning of a male Dugong after his female had been captured and killed
- [...] Once I saw two large Dugungs or sea cows, they came very close to the rocks on my pleasure house. I quickly had the man called and showed him the sea cows walking around and eating the green moss that grows on the reef. [...] they stung one of them, that was the woman [. ..]. When the latter was caught, the other, who was the male, came by himself, looked for the female, did not go away, and was also stung; So they both brought them ashore [...]. Each of these miracle fish was over six cubits long, but the male was slightly larger than the female. They had heads like an ox, two large ones, one span long, and teeth as thick as a thumb, which protruded from their throats, like those of wild pigs. These teeth were as white as the most beautiful ivory. The woman had two breasts like a woman's picture, and the man a patrimony as a man-person, her entrails were like those of a bark, and the meat tasted the same as the beef.
The French author Jules Verne included the dugong in his work 20,000 Leagues Under the Sea , in which the protagonists encounter a dugong whose size, at seven meters in length, is clearly exaggerated. However, it corresponds to the larger species of this family that became extinct through hunting in the second half of the 18th century. The sharp decline in the Red Sea population due to intensive hunting is addressed.
- [...] His flesh, a real flesh, is extremely valued, [...]. That is why one hunts this excellent animal so fiercely that, like the manatee, its tribal member, it is becoming increasingly rare.
Also there the animal is called by one of the protagonists
- Genus manatees, family mammals, order vertebrates, class chordates
classified, which clearly shows the great uncertainty of the classification and the differences between today's and the then systematics. The animal is harpooned in the story, whereupon it flees. Eventually, even with today's knowledge rather unlikely, the dugong attacked the boat. In the end, the dugong is killed and consumed. In the novel The Mysterious Island , the dugong is also portrayed as an aggressive animal that attacks a dog and ultimately falls victim to a larger sea creature.
swell
- David MacDonald (Ed.): The Great Encyclopedia of Mammals . Könemann im Tandem Verlag, Königswinter 2004, ISBN 3-8331-1006-6 . (Translation of the original English edition from 2001)
- Paul K. Anderson, Jane M. Packard, Galen B. Rathbun, Daryl Domning, Robin Best: Manatees . Pp. 278-287.
- Helene Marsh: On green seagrass meadows. Pp. 288-289 (Ingestion of the dugongs).
- F. Kurt: The dugong. In: Bernhard Grzimek (Ed.): Grzimeks Tierleben Mammals 3 . Bechtermünz Verlag, Augsburg 2000, ISBN 3-8289-1603-1 , pp. 529-532. (Reprint of the original dtv edition from 1979/80)
- Sandra L. Husar: Dugong dugon. In: Mammalian Species . 88, The American Society of Mammalogists 1978 (PDF; 882 kB)
- Martin S. Fischer: Sirenia, manatees. In: W. Westheide, R. Rieger: Special Zoology. Part 2: vertebrates or skulls. Spektrum Akademischer Verlag, Munich 2004, ISBN 3-8274-0307-3 .
- Ronald M. Nowak: Walker's Mammals of the World . Johns Hopkins University Press, 1999, ISBN 0-8018-5789-9 .
- Dugong dugon in the Red List of Threatened Species of the IUCN 2006. Posted by: H. Marsh, 2006. Retrieved on January 20 of 2007.
Web links
- IUCN report on the status of the Dugong (PDF file; 11.69 MB)
- The dugong hunt , section from 20,000 leagues under the sea
- Knowledge before eight - nature ∙ The first: Strange animal beings: the dugong. Retrieved March 10, 2020 .
Individual evidence
- ↑ Sir Henry Yule: Hobson-Jobson: A Glossary of Colloquial Anglo-Indian Words and Phrases, and of Kindred Terms, Etymological, Historical, Geographical and Discursive . J. Murray, London 1903. p. v. dugong, s. ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (P. 330)
- ^ Oeuvres complètes de Buffon, suivies de ses continuateurs . Th. Lejeune, Brussels 1830. Volume IV, p. 367.
- ↑ OED Online , s. v. dugong, n. Oxford University Press, 2008. << http://www.oed.com/view/Entry/58283?redirectedFrom=dugong > (restricted access, accessed April 21, 2013); see Jo Frid. Gmelin [di Johann Fridrich Gmelin]: Caroli a Linné systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis ... Editio decima tertia, aucta, reformata . Georg Emanuel Beer, Leipzig 1788–1793. Volume 1, Part 1: Mammalia . P. 60. ( Digitized on the pages of the Biodiversity Heritage Library ).
- ^ Ernst Christoph Barchewitz. Newly augmented East Indian travel description…. His eleven-year stay on Java, Banda and the Southwestern Islands…. Erfurt 1751, pp. 381-382
