Chocolate shark

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Chocolate shark
Dalatias licha.jpg

Chocolate shark ( Dalatias licha )

Systematics
Sharks (selachii)
Superordinate : Squalomorphii
Order : Spiny dogfish (Squaliformes)
Family : Dalatiidae
Genre : Bird's beak dogfish
Type : Chocolate shark
Scientific name of the  genus
Dalatias
Rafinesque , 1810
Scientific name of the  species
Dalatias licha
( Bonnaterre , 1788)

The chocolate shark ( Dalatias licha ) belongs to the Dalatiidae family and is the only species of the bird-billed dogfish ( Dalatias ) genus . It is found in various, demarcated areas of the deep sea worldwide and has an average body length of around 1.20 meters. The German common name “chocolate shark ” is derived from its deep brown color; in the English-speaking world this species is known as the kitefin shark (literally translated as dragonfin shark ).

The shark feeds mainly on bony fish and invertebrates . In addition, thanks to its jaw shape, it can bite pieces of meat from larger animals, such as large sharks and whales. The chocolate shark is primarily fished in Japan, Portugal and South Africa, mainly for the liver oil and the skin that is made into leather. The International Union for Conservation of Nature (IUCN) classified it as a type of warning list due to the fishing pressure worldwide and as endangered in the north-eastern Atlantic based on the available data.

features

Head of the chocolate shark with large eyes, a short snout and thick lips

The very slim chocolate shark reaches an average body length of 1.20 meters with an average weight of 8 kilograms, but in individual cases it can be up to 1.60 or 1.80 meters long. Its body is deep brown to gray, sometimes also light purple or black, on the back as well as on the flanks and the belly side, only the area around the mouth is white. Faint black spots may appear on the back, the edges of the fins are white or translucent, and the tip of the tail is black. In 2003 a partially albino specimen was caught in the Gulf of Genoa , with about 59 percent of the body surface missing the dark color. Unlike an earlier case of an albinotic Portuguese shark , the ability to catch prey was not affected by this discoloration.

The snout is very short and rounded, the mouth appears straight when viewed from below. The lips are thick and wrinkled or fringed. The large, three-pointed teeth of the lower jaw stand in 17 to 20 rows of teeth, each forming a saw-like structure with a common cutting edge. The elongated, curved upper jaw teeth are much smaller, have only one point and are in 16 to 21 rows of teeth. The very large eyes and nasal pits and also the rather large spray hole are striking . The five gill slits are all parallel in front of the attachment of the pectoral fin.

The shark has two conspicuous dorsal fins, which, unlike other dogfish species, have no fin spines. The rear dorsal fin is slightly larger than the front. The first dorsal fin arises behind the free end of the pectoral fins, while the second dorsal fin starts above the base of the pelvic fin. The pectoral fins are relatively small, but the pelvic fins are noticeably large and there is no anal fin. The caudal fin consists of two parts (lobi) and is asymmetrical, with a very short lower and a large upper lobe, which also has a large end lobe. The chocolate shark differs from the outwardly similar Portuguese shark ( Centroscymnus coelolepis ) mainly in the lack of fin spines. The skin flakes are small and flat and have a single horizontal ridge.

distribution

Distribution areas of the chocolate shark

The chocolate shark is common in the tropical and warm temperate seas worldwide; Only a small amount of gene exchange takes place between the numerous individual populations . The main distribution area is in the eastern Atlantic from the Scottish coast to Morocco and off Madeira and the Azores as well as in the western Atlantic in the area of ​​the Georges Bank in the Gulf of Maine and in the northern Gulf of Mexico . You can also find it in the Mediterranean , especially in the Aegean Sea , and as an errant also in the North Sea . From the southern Atlantic there is only one evidence from southern Brazil . It also lives in the Indian Ocean and the Pacific and can be found regularly off the coasts of Southeast Africa ( South Africa and Mozambique ), Australia , New Zealand , Japan and Hawaii . There are no finds for the northern part of the Indian Ocean or the eastern Pacific.

As a deep-sea species, the shark can normally be found at depths between 90 and 1800 meters, especially in the range of 200 to 600 meters. In the area of ​​the Azores there is a segregation of the species according to sex, with the females usually staying at a depth of about 230 meters and the males at depths between 412 and 448 meters. The chocolate shark inhabits the outer areas of the continental shelf and the upper area of ​​the continental slopes , it also lives in the area of ​​islands and seamounts. It is the only species in its family that is more commonly found near the sea floor than in the water column, but it can occasionally be caught well above the bottom.

Way of life

Chocolate sharks are relatively common in their areas of distribution. They are usually solitary but can also form small groups. They are slow swimmers and have a large liver with a high proportion of squalene , which gives them buoyancy due to its low density and thus enables them to swim and stand in the water column without any effort.

According to studies on the South African coast and in the Gulf of Genoa , the ratio of males to females in these places is 2: 1 to 5: 1; However, since corresponding distributions could not be detected in other locations, it is very likely that there are errors in the sampling or local phenomena.

nutrition

The chocolate shark's lower row of teeth forms a continuous cutting surface that allows it to bite pieces of meat from larger animals.

The chocolate shark is a strong and adaptable deep-sea hunter whose short and sturdy jaws give it great bite force. It feeds mainly on bony fish of the deep sea as gold salmon , Viper fish , Barten dragon fish , barracudina , green eyes , lantern fish , bristle mouths , cod , grenadiers , deep-sea scorpion fish , mackerel , snake mackerel , deepwater cardinal perch or sea toad . In addition to these, he preyed on a number of other prey, including rays , smaller sharks ( Galeus , Squalus , Etmopterus and Centrophorus ), octopus and other cephalopods, crustaceans , bristle worms and state jellyfish . Like the closely related cigar sharks , the chocolate shark is also able to bite pieces of meat from larger animals, including large species of sharks and whales . With evidence of fast swimming species in its diet, it is believed that chocolate sharks also eat carrion or have developed methods by which they can also prey on fast swimmers. In the Mediterranean, bony fish are the shark's main diet year round, followed by small sharks in winter and spring, crustaceans in summer and cephalopods in autumn. Among the captured animals, the males, in contrast to the females, usually have a full stomach; the reason for this difference is not known.

Predators and parasites

The chocolate shark is mainly preyed on by larger bony fish and sharks. It is also part of the food spectrum of the sperm whale ( Physeter macrocephalus ). Information about parasite infestation of this type is sparse. Two individuals who were caught off the coast of Ireland, three species were of nematodes are found, one of which as Anisakis simplex (L 3 -Larvenstadium) could be identified and another probably the larva of a Raphidascaris was -Art.

Reproduction and development

Chocolate sharks give birth to their young animals alive, whereby these develop without a placenta inside the womb (uterus) and are nourished by a yolk supply (aplacental viviparous ). The adult females have two functioning ovaries and two uteri that are not divided. There is no separate reproductive phase. In the Mediterranean, young animals are born all year round, with an increase in the birth rate in spring and autumn. The females probably have a break of about a year between gestation periods.

The number of juvenile sharks is between 10 and 16 and increases with the size of the females. At birth, after a development period of around two years, they are 30 to 45 centimeters long, which varies depending on the region.

The male sharks reach sexual maturity with a length of 77 to 121 centimeters, the females only with a body length of 117 to 159 centimeters. There is no connection between the individual size at birth, the size required to reach sexual maturity and the later maximum body length of the individual animals.

Evolution and systematics

The oldest fossil teeth that can be clearly assigned to the chocolate shark come from the Middle Eocene, such as those found in the Bortonia layers of New Zealand , which are estimated to be 43 to 37 million years old. In addition, were Dalatias -Zähne different ages in Europe , the former Soviet Union , Japan and western India found. The fossils assigned to this species today are historically described under a variety of different names.

The cigar shark ( Isistius brasiliensis ), known for eating chunks of meat from larger fish, is the chocolate shark's closest relative.

The first scientific description of the chocolate shark was made under the name Squalus licha by the French naturalist Pierre Joseph Bonnaterre in his Tableau encyclopédique et méthodique des trois regnes de la nature of 1788. The type specimen which, according to his description, came from "Le cap Breton", got lost. Later, the shark was classified in its own genus Dalatias through the description of the synonym Dalatias sparophagus by Constantine Rafinesque in 1810. On this basis, the current generic name is rejected by some scientists as the noun dubium and the third available name, Scymnorhinus , is preferred.

On the basis of phylogenetic studies it is now assumed that the closest relatives of the chocolate shark within the Dalatiidae are the cigar sharks (genus Isistius ), with which it shares a number of common features of teeth, skeleton and muscles.

 Dalatiidae  

 other Dalatiidae


  NN  

 Chocolate shark ( Dalatias licha )


   

 Cigar sharks (genus Isistius )




A separation of the two species is for the period shortly after the Cretaceous-Tertiary boundary adopted, before about 65.5 million years ago, as a result of adaptive radiation by adjusting the coming from the deep sea dogfish in relatively shallow marine zones and shallow water habitats.

Relationship to people

Because of the habitats in the deep sea on continental slopes as well as its small size, the chocolate shark is harmless to humans. The shark's teeth were found in deep-sea cables that the animals had probably bitten into.

Japanese scientists surveying a chocolate shark.

In Japan, South Africa as well as in Portugal and Spain in particular, the chocolate shark is used together with other shark species, above all the Portuguese shark ( Centroscymnos coelolepis ), in various ways as food fish (usually salted and cured) and as a supplier of liver oil or leather. The skin is used as real shagreen for various jewelry items and for a Spanish polished leather known as " boroso ". It is also processed into fish meal together with other types of bycatch . The shark is not used in the western Atlantic.

The increasing and continuous expansion of commercial fishing in the deep sea area has increasingly led to overfishing and a decline in these and other deep sea species, which usually have slow growth rates, long reproduction times and low numbers of offspring. As a result, commercial fishing for these and other species collapsed, especially in the Azores. Commercial fishing for the chocolate shark began here in the early 1970s to obtain the sharks' liver oil. In the early 1980s the fishing fleet was enlarged and industrialized through the use of bottom trawls . In 1984 a maximum of 937 tonnes was caught as a result, after which the shark catch fell rapidly and was less than 15 tonnes per year after 1991, which is why the fishery had to be stopped at the end of the 1990s while the liver oil price fell at the same time. A study of the populations has shown that the fishery has reduced the stocks of this species in the northwestern Atlantic to about half of the original biomass.

Portugal and Japan account for the largest share of chocolate shark catches, with the sharks being brought in mainly as bycatch in trawling and longline fishing. Portugal reported a catch of 282 tonnes in 2000 and 119 tonnes of chocolate sharks in 2003. In other areas of the north-eastern Atlantic this shark is comparatively rare and the stated catch numbers are often unusable due to confusion with other shark species. Some of the sharks are caught in the unspecific net fishery in the deep sea area west of the British Isles, where it is estimated that stocks have declined by up to 94 percent since the 1970s. The shark is not fished directly in the Mediterranean either and is usually landed as bycatch. Although they are usually thrown back into the water alive, most individuals do not survive. In the area of ​​Australia the catch numbers are increasing mainly due to the relaxation of the regulations for the maximum mercury content in fish and seafood. The chocolate shark is not affected by a quota system. In New Zealand, fishing for this species peaked between 1986 and 1997 and has since declined. The International Union for Conservation of Nature (IUCN) classified the chocolate shark accordingly worldwide as a type of the warning list (“near threatened”) and in the north-eastern Atlantic as endangered (“vulnerable”) based on the available data.

literature

Web links

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

Individual evidence

  1. ↑ a b c d Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean , Franckh-Kosmos Verlags-GmbH, Stuttgart 2005; Pp. 118-119. ISBN 3-440-10458-3
  2. ^ A b c d Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton Field Guides, Princeton University Press, Princeton and Oxford 2005; Page 125. ISBN 978-0-691-12072-0
  3. ↑ a b c d e f g h Bester, C. and Burgess, G. Biological Profiles: Kitefin Shark . Florida Museum of Natural History Ichthyology Department. Retrieved on June 15, 2009.
  4. ↑ Bottaro, M., Ferrando, S., Gallus, L., Girosi, L. and Vacchi, M. (2005). First record of albinism in the deep water shark Dalatias licha ( Memento from September 25, 2006 in the Internet Archive ) Reference No. 5115. JMBA2-Biodiversity Records.
  5. ↑ a b c d e f g h i Compagno, LJV: Sharks of the World: An Annotated and Illustrated Catalog of Shark Species Known to Date . Food and Agricultural Organization, Rome 1984, ISBN 9251013845 , pp. 63-64.
  6. ↑ a b c d Fowler, SL, Cavanagh, RD, Camhi, M., Burgess, GH, Cailliet, GM, Fordham, SV, Simpfendorfer, CA and Musick, JA: Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes . International Union for Conservation of Nature and Natural Resources, 2005, ISBN 2831707005 , pp. 230-231.
  7. ^ A b c d Soto, JMR and Mincarone, MM: First record of kitefin shark, Dalatias licha (Bonnaterre, 1788) (Chondrichthyes, Dalatiidae), in the south Atlantic . In: Mare Magnun . 1, No. 1, 2001, pp. 23-26.
  8. ↑ a b c d e f g Dalatias licha in the endangered species Red List of IUCN 2006. Submitted By: Blasdale, T., F. Serena, C. Mancusi, J. N. and Guallart Ungaro, 2008. Retrieved on. 6 April 2010.
  9. ↑ a b Kiraly, SJ, JA Moore and PH Jasinski: Deepwater and Other Sharks of the US Atlantic Ocean Exclusive Economic Zone . In: Marine Fisheries Review . 65, No. 4, 2003, pp. 1-63.
  10. ↑ a b c Carrier, JC, Musick, JA and Heithaus, MR: Biology of Sharks and Their Relatives . CRC Press, 2004, ISBN 084931514X , p. 58.
  11. ↑ a b c Capapé, C., Hemida, F. and Quignard, JP: Biological observations on a rare deep-sea shark, Dalatias licha (Chondrichthyes: Dalatiidae), off the Maghreb coast (south-western Mediterranean) . In: Pan-American Journal of Aquatic Sciences . 3, No. 3, 2008, pp. 355-360.
  12. ^ A b Musick, JA and McMillan B .: The Shark Chronicles: A Scientist Tracks the Consummate Predator . Macmillan, 2003, ISBN 0805073590 , pp. 122-123.
  13. ^ Gómez-Villota, F. (2007). Sperm whale diet in New Zealand. Master of Applied Science thesis. Auckland University of Technology.
  14. ↑ Henderson, AC, Flannery, K. and Dunne, J .: Biological observations on shark species taken in commercial fisheries to the west of Ireland . In: Biology and Environment . 103B, 2003, pp. 1-7.
  15. ↑ da Silva, HM (1988): Growth and reproduction of kitefin shark, Dalatias licha (Bonn 1788) in Azorean waters. ICES, Demersal Fish Committee CM 1988 / G: 21, pp. 1-16.
  16. ^ A b Keyes, IW: New records of fossil elasmobranch genera Megascyliorhinus , Centrophorus , and Dalatias (Order Selachii) in New Zealand . In: New Zealand Journal of Geology and Geophysics . 27, 1984, pp. 203-216.
  17. ↑ a b Adnet, S. and Cappetta, H .: A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes: Squaliformes) based on dental characters . In: Lethaia . 34, No. 3, September 2001, pp. 234-248. doi : 10.1111 / j.1502-3931.2001.tb00052.x .
  18. ↑ Shirai, S .: Phylogenetic Interrelationships of Neoselachians (Chondrichthyes: Euselachii) . In: Stiassny, MLJ, Parenti, LR and Johnson, GD (eds.): Interrelationships of Fishes . Academic Press, 1996, ISBN 0126709505 , pp. 9-34.
  19. ↑ a b ICES. (2007). Report of the Working Group Elasmobranch Fishes (WGEF), June 22-28, 2007, Galway, Ireland. ICES CM 2007 / ACFM: 27. pp. 52-55.
  20. ↑ a b Perrotta, R .: Kitefin shark, Dalatias licha (dalatiidae) fishery in the north eastern Atlantic and some recommendations for elasmobranchs exploitation . In: Revista de Investigación y Desarollo Pesquero . 16, 2004, pp. 97-101.
  21. ↑ Castro, JI, Woodley, CM and Brudek, RL (1999). A preliminary evaluation of the status of shark species. FAO Fisheries Technical Paper No. 380
This version was added to the list of articles worth reading on May 22, 2010 .