nurse shark

nurse shark

Only Atlantic species (Ginglymostoma cirratum) of 25 carpet shark species (family Orectolobidae). Yellow- or gray-brown, sometimes with dark spots, it may grow to over 13 ft (4 m) long. It may attack swimmers, especially when provoked, but is not related to the dangerous gray nurse (Odontaspis arenarius), a sand shark.

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The grey nurse shark (Australia), spotted ragged-tooth shark (Africa) or sand tiger shark (US and UK), Carcharias taurus, is a large shark inhabiting coastal waters worldwide, with many different names in different countries in the world. Despite a fearsome appearance and strong swimming abilities, it is a relatively placid and slow moving animal. It is considered not aggressive unless provoked.

Anatomy and appearance

The body is stout, with two large dorsal fins and the tail is elongated and has a long upper lobe. The shark has a precaudal pit but no caudal keels. It grows to a length of 3.2 m (about 10.5 ft). Male grey nurse sharks mature at 2.1 m (about 6' 11"); and females mature at 2.2 m (about 7' 3"). This shark weighs 90 to 160 kg (200 to 350 lb).

The grey nurse shark usually has a grey back and white underside. In August 2007, an albino specimen was photographed off South West Rocks, Australia.

Diet

The diet of Carcharias taurus consists of bony fishes including mackerels, other sharks and rays, squids, crabs and lobsters.

Behaviour

The sharks typically congregate in coastal waters, at depths of between 60 and 190 m, although deeper depths have been recorded. Often they will shelter in caves or gutters during the day, and come out at night to feed. During the day they exhibit sluggish behavior, becoming more active during the night. The grey nurse shark is the only known shark to gulp and store air in its stomach in order to maintain neutral buoyancy while swimming.

While it is commonly reported that grey nurse sharks are harmless , data compiled by ISAF records 76 attacks on humans, of which 29 have been classified as unprovoked. Two of those unprovoked attacks have resulted in fatalities.

However, it can be calm during daytime and in aquariums it is a very common species.

Reproduction

The species is ovoviviparous, i.e. bearing live young from eggs which hatch inside the uterus. Female sharks have two uteruses. Inside the uterus the young sharks develop and eat each other, so typically only two young sharks are born for each gestation period, which lasts six to nine months. This process, also known as intrauterine cannibalism, is making it harder for the shark population to rebound from near extinction. As a result, scientists plan to artificially inseminate and breed the sharks, in order to increase their population. Another plan is to remove the shark embryos from the uterus before cannibalism can take place and then artificially gestate them.

Conservation status

It is listed as vulnerable on the IUCN Red List, and as endangered under Queensland's Nature Conservation Act 1992. For further information on conservation status and measures, see grey nurse shark conservation.

See also

Gallery

Footnotes

References

  • Database entry includes justification for why this species is vulnerable
  • Barry Bruce, John Stevens, Nick Otway: Site fidelity, residency times and activity space in grey nurse sharks in eastern Australia

External links

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