Whale shark

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Whale shark
Whale shark near Dharavandhoo (Indian Ocean), an island in the Maldives in the Baa Administrative Atoll

Whale shark near Dharavandhoo (Indian Ocean), an island in the Maldives in the Baa Administrative Atoll

Systematics
Superordinate : Galeomorphii
Order : Nurse Shark (Orectolobiformes)
Subordination : Orectoloboidei
Family : Whale sharks
Genre : Whale sharks
Type : Whale shark
Scientific name of the  family
Rhincodontidae
Müller & Henle , 1839
Scientific name of the  genus
Rhincodon
A. Smith , 1829
Scientific name of the  species
Rhincodon typus
A. Smith , 1828

The whale shark ( Rhincodon typus ) is the largest shark and also the largest fish today. It is the only species of the genus Rhincodon , which in turn is the only genus within the family Rhincodontidae . The whale shark belongs to the order of the nurse shark-like .

The longest specimen of a whale shark measured so far was 13.7 m. There are reports based on sightings of specimens up to 18 or 20 m long, but these are probably based primarily on an overestimation and exaggeration, which is particularly common in large animals. In February 2012, Pakistani fishermen pulled an approximately 13 m long specimen ashore in the port of Karachi. Whale sharks can weigh over 12 tons. They feed similar to basking sharks and giant sharks mouth of plankton and other micro-organisms (krill), which they by sucking the water filter . According to recent studies, however, they also eat fish up to the size of mackerel and small tuna , i.e. up to about one meter. Because of its food specialization, this shark is harmless to humans, so snorkeling trips with whale sharks are offered in the north of Western Australia , for example . However, accidents can occur due to the size and strength of the animals, so a minimum distance must be maintained.

Synonyms are R. typicus Müller & Henle, 1839, R. pentalineatus Kishinouye, 1891, R. typus Smith, 1829, R. typus Smith, 1828 and Micristodus punctatus Gill, 1865.

features

Whale sharks are greyish, brownish or bluish in color. The belly is brightly colored, the back is covered with bright stripes and spots arranged in transverse lines. The large mouth extends the full width of the flattened and blunt snout. It is the only representative of the sharks to have a terminal mouth . The approximately 3600 small teeth are arranged in more than 300 close rows. The animals have five gill slits, two dorsal fins and pectoral and anal fins. The upper lobe of the caudal fin is about a third longer than the lower. With a thickness of up to 15 cm, its skin is the thickest of all living things on earth.

Distribution and way of life

distribution

Rhincodontidae prefer a water temperature of 21 to 25 ° C and can be found in almost all warm, tropical and subtropical waters worldwide, although there are regions in which they occur more frequently. As a rule, these are areas with seasonal plankton bloom or regions in which plankton-rich, colder upwelling water can be observed. Whale sharks often migrate between offshore and offshore areas. Male whale sharks cover considerable distances, female only shorter ones; they seem to return regularly to the area of ​​their birth. Male sharks also return to certain spots on a regular basis. They occur singly, but also in groups. Such gatherings can bring together over 400 individuals, feeding on large clusters of fish larvae.

Whale sharks actively suck in the water (up to 6000 l / h) and squeeze it out again through their gills, which are equipped with a sponge-like filter device. This is formed from cartilage clasps that connect the individual gill arches like a grid and on which matted skin teeth sit. In order to meet their enormous food needs, they filter not only plankton but also small fish and other marine life from the water. Often they "stand" vertically in the water, their heads pointing towards the surface of the water, or they move the head protruding from the water from one side to the other and open and close their mouths (7–28 times per minute).

Reproduction

Size comparison to humans
Whale shark in the Gulf of Thailand
Whale shark at Isla Blanca , Quintana Roo , Mexico (Video, 30s.)

The discovery of an egg with a size of approximately 30 × 14 × 9 cm with a 36 cm large whale shark embryo in 1953 in the Gulf of Mexico seemed to confirm the earlier assumption that whale sharks were one of the egg-laying shark species. It was not until a pregnant female was caught off Taiwan in 1995 and the scientific investigation of this specimen revealed that whale sharks can give birth to up to 300 live cubs. However, these young are not all at the same stage of development as many other shark species are. Rather, different young and older forms of embryonic development exist in parallel. The more developed they are, the closer the young are to the birth opening. The female can probably control the development and thus the birth for many years and only gives birth if she estimates the chances of her young to survive as high. This is presumably closely related to the availability of food, the currents and the temperatures of the water. These assumptions are not yet adequately proven, but the most likely explanation for this peculiarity. The egg found was probably one that was lost prematurely. Usually, the sharks hatch in the uterus with a size of 58 to 64 cm. The smallest specimen found was about 40 cm in length and was found in shallow water near the coastal town of Donsol in the Philippine province of Sorsogon . The sea area near Donsol is possibly a breeding area for whale sharks.

One can only guess where the boys develop after birth until they reach sexual maturity. It is likely that they will develop further at greater depths. Possibly below a depth of 300 meters, since above that they could still represent food competitors for their adult conspecifics. This would be a disadvantage for young and old. They may be venturing into deeper layers of water that their parents cannot reach.

The whale shark only reproduces between the ages of 10 and 30 years and can live up to 100 years.

Tribal history

A predecessor of today's whale shark was described with the Palaeorhincodon . The genus goes back to J. Herman from 1974 and is based on finds from the Brussels and Leder sands in Belgium , which date to the Middle Eocene . Other remains come from Dormaal , also Belgium. But they should already belong to the Lower Eocene. Generally, the remains of Palaeorhincodon rare but widely distributed fairly and were both in southwestern France and in North America -a-days, where they, among other things from Fishburne formation in South Carolina , and from the Hardie mine local fauna in Georgia , both United States , exist . Around 40 teeth have been recovered from the phosphate-rich deposits of the Ouled Abdoun Basin in Morocco . They date from the Upper Paleocene to the Lower Eocene. Further teeth have been reported from the Eocene phosphate basin of Kpogamé-Hahotoé in Togo . The teeth of Palaeorhincodon are strongly pressed and relatively small, maximum 4 mm high. The main tip is bent backwards (frontal teeth) or to the side (lateral teeth) depending on the position in the mouth. At the side, the main peak is usually accompanied by a smaller secondary peak. The latter distinguishes Palaeorhincodon from today's whale shark, in which the secondary tips are missing.

threat

The IUCN classified the whale shark as critically endangered in 2016 . It is therefore on the red list. The population trend is pointing down. The whale shark is threatened by fishing, aquaculture, oil drilling, shipping and people who come too close to it during recreational activities.

Sources and further information

Individual evidence

  1. ↑ Pakistan: Fishermen heave huge whale sharks out of the docks. In: Spiegel Online . February 7, 2012, accessed January 22, 2017 .
  2. ↑ Planet Earth , average report
  3. ↑ Alberto Siliotti and others: Memofish Book - The fish of the Red Sea , Geodia Verlag Verona, 2002, ISBN 88-87177-43-0 .
  4. ^ Exmouth Visitor Center , Official Tourist Office website
  5. ↑ a b c FAO Fisheries and Aquaculture Department
  6. ^ The modern animal dictionary , Bertelsmann Publishing Group, Volume 11, 1981.
  7. ↑ The Shark's Body Structure - The Skin ( Memento from June 17, 2010 in the Internet Archive )
  8. ↑ a b c whale shark on Fishbase.org (English)
  9. ^ R. de la Parra Venegas, R. Hueter, J. González Cano, J. Tyminski, J. Gregorio Remolina, M. Maslanka, A. Ormos, L. Weigt, B. Carlson & A. Dove (2011): An Unprecedented Aggregation of Whale Sharks, Rhincodon typus, in Mexican Coastal Waters of the Caribbean Sea PLoS ONE, 6 (4) doi : 10.1371 / journal.pone.0018994 .
  10. ↑ Premiere: Fishermen find living whale shark baby. In: Spiegel Online . March 9, 2009, accessed January 22, 2017 .
  11. ↑ J. Herman: Compléments paléoichthyologiques à la faune Eocene de la Belgique. 1. Palaeorhincodon, genre nouveau de l'Eocène belgium. Bulletin de la Société Belge de Géologié 83 (1), 1974, pp. 7-13 ( [1] )
  12. ^ Richard Smith: Elasmobranches nouveaux de la transition Paléocène-Eocène de Dormaal (Belgique). Bulletin de l'institut royal de sciences naturelles de belgique 69, 1999, pp. 173-185
  13. ^ A b Gerard R. Case, Todd D. Cook and Mark VH Wilson: A new elasmobranch assemblage from the early Eocene (Ypresian) Fishburne Formation of Berkeley County, South Carolina, USA. Canadian Journal of Earth Sciences 52 (12), 2015, pp. 1121-1136
  14. ↑ Dennis Parmley and David J. Cicimurri: Late Eocene sharks of the Hardie Mine local fauna of Wilkinson County, Georgia. Georgia Journal of Science, 61, 2003, pp. 153-179
  15. ↑ a b Abdelmajid Noubhani and Henri Cappetta: Les Orectolobiformes, Carcharhiniformes et Myliobatiformes (Elasmobranchii, Neoselachii) des bassins à phosphate du Maroc (Maastrichtien-Lutétien basal). Systématique, biostratigraphie, évolution et dynamique des faunes. Palaeo Ichthyologica 8, 1997, pp. 1-327
  16. ↑ Rhincodon typus (Whale Shark). In: iucnredlist.org. March 31, 2016, accessed January 22, 2017 .
  17. ^ The IUCN Red List of Threatened Species. Retrieved October 17, 2018 .

Web links

Commons : Whale Shark  - Collection of pictures, videos and audio files
Wiktionary: Whale shark  - explanations of meanings, word origins, synonyms, translations