Bull shark

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Bull shark
Bullshark Beqa Fiji 2007.jpg

Bull shark ( Carcharhinus leucas )

Systematics
without rank: Sharks (selachii)
Superordinate : Galeomorphii
Order : Ground Sharks (Carcharhiniformes)
Family : Requiem sharks (Carcharhinidae)
Genre : Carcharhinus
Type : Bull shark
Scientific name
Carcharhinus leucas
( Müller & Henle , 1839)

The bull shark or common ground shark - sometimes also called bull shark or Zambezi shark ( Carcharhinus leucas ) - is a shark from the family of Requiem sharks (Carcharhinidae).

anatomy

The bull shark owes its name to its physique. This looks compressed with a weight of up to 230 kg and a length of 330 cm, and the more wide than long snout reinforces this bullish impression. The bull shark is easy to distinguish from other sharks by its almost right-angled dorsal fin and the lack of an interdorsal ridge between the anterior and posterior dorsal fin.

distribution

Bull shark in the riparian zone
Distribution areas of the bull shark

It can be found in both fresh and salt water. He prefers shallow water near the banks and in the estuary of the rivers and thus takes advantage of the poor underwater visibility, which occurs even in the slightest swell and through the mixing of fresh and salt water. Its habitat is in all warmer coastal areas of

where he ventures deep into the interior of the rivers and can also be found in lakes. So it got over the Río San Juan into the Central American Nicaragua Lake , where larger populations have formed over time.

Physiologically, in contrast to many other sharks, the bull shark is able to operate an adapted osmoregulation via the kidneys . When the shark swims from the sea water into the fresh water of a river, the metabolism of the kidneys continuously adapts to the extent that fewer salts and, in return, more urea are filtered out of the blood. This reversal of the normal osmoregulation for the shark enables it to survive in freshwater for longer periods of time.

Freshwater forms

Nicaragua shark

The bull sharks found in Lake Nicaragua have been described as a separate species, Carcharhinus nicaraguensis , but have not been scientifically recognized.

In the 1960s, it was found that Nicaraguan sharks, like salmon, can negotiate the rapids of the San Juan River and thus have an exchange with the Caribbean Sea. Sharks tagged in Lake Nicaragua were caught in the Caribbean 7 to 11 days later. Thomas B. Thorson from the University of Nebraska observed the migration cycle of the Nicaraguan shark in long-term studies from 1960 to 1982. The greatest population density exists in the lower reaches of the San Juan and the mouth of the Rio Colorado in Costa Rica . The reproduction takes place in brackish water and not in the lake. Only 10 to 12% of the bull sharks that soar in the San Juan end up in Lake Nicaragua, as many animals are caught by professional fishermen for their skin, dorsal fins and meat. In 1975 the government of Costa Rica issued numerous protective measures for the bull shark, the catch quota in 1980 was 113 tons / year. The populations have declined rapidly since then, as it would probably take 20 years for the population to recover due to the reproduction cycle, the long gestation period and the low progeny.

Zambesi shark

In contrast to the Nicaragua shark, the Zambesi shark is a local subspecies of the bull shark. The Zambesi shark occurs in the warmer, heavily clouded coastal rivers of the regions of KwaZulu-Natal , Eastern Cape and Mozambique . During floods in the Transkei , zambesi sharks find rich prey from dead grazing animals that are washed downstream and penetrate far into the river systems. The bull shark is known to be an opportunistic predator who does not specialize in any particular prey on their hunting trips. In the summer months it is also considered a threat to humans. In the Breede River , whose estuary near Witsand in St. Sebastian Bay is considered a breeding area for juvenile fish, a pregnant female of a zambezi shark, 4 m long and weighing 600 kg, was caught in 2008, which is an absolutely exceptional size.

Ganges bull shark

Another subspecies of the bull shark occurs in the lower reaches of the Ganges in India , which is often confused with the gangeshai ( Glyphis gangeticus ). The frequent flooding and Indian funeral rites can lead to accidents as bull sharks swim up the rivers looking for carcasses.

Reproduction

A pregnant bull shark on Shark Reef, Fiji

The litter size is 1 to 13 live-born pups, the gestation period 10 to 11 months. Males become sexually mature at 14 to 15 years of age, females at around 18 years of age.

food

It feeds on bony fish , other sharks, but also crustaceans , rays and molluscs .

Bull shark and human

The bull shark, along with the tiger shark and the great white shark, is one of the sharks that are blamed for most of the shark attacks on humans. The Florida Museum of Natural History's International Shark Attack Files lists 75 unprovoked attacks and 23 deaths. Many experts believe that many of the great white shark-related attacks on humans actually come from the bull shark. The main reason for possible mix-ups is assumed to be the similar teeth and thus hardly distinguishable bite marks of the two species.

literature

  • Henry B. Bigelow, William C. Schroeder: Carcharhinus Nicaraguensis, a Synonym of the Bull Shark , C. Leucas Harvard University
  • Edward Marriott, Savage Shore: Life and Death with Nicaragua's Last Shark Hunters , Metropolitan Books Travel ISBN 0-8050-5555-X
  • Erich Ritter: Haie - people - encounters , Shark School ISBN 978-3-00-033388-0

Web links

Commons : Bull Shark  - Collection of images, videos and audio files

supporting documents

  1. Shark Savers :: How Bull Sharks Survive in Fresh Water. Retrieved June 11, 2018 .
  2. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1035&context=ichthynicar
  3. Main shark page - Sharks in south africa ( Memento from December 15, 2007 in the Internet Archive )
  4. Breede A 'Nursery' For Zambezi Sharks. (No longer available online.) Archived from the original on August 9, 2009 ; accessed on June 16, 2018 (English).
  5. Huge Zambezi shark caught in Breede River: Treevolution
  6. ^ Shark Science & Intern Opportunities l South African Shark Conservancy . In: South African Shark Conservancy . ( sharkconservancy.org [accessed June 16, 2018]).
  7. Bull Shark (Carcharhinus leucas) Information and Classification ( Memento of July 14, 2011 in the Internet Archive )
  8. Fact Sheet: Bull sharks at sharkinfo.ch