| Sand tiger shark | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Order: | Lamniformes |
| Family: | Odontaspididae |
| Genus: | Carcharias |
| Species: | C. taurus |
| Binomial name | |
| Carcharias taurus Rafinesque, 1810 |
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| Range of the sand tiger shark | |
The sand tiger shark (Carcharias taurus), grey nurse shark, spotted ragged tooth shark, or blue-nurse sand tiger is a species of shark that inhabits coastal waters worldwide. It lives close to the shorelines and sandy beaches of North America, hence the name sand tiger shark. It also dwells in the waters of Japan, Australia, and South Africa. Despite its fearsome appearance and strong swimming ability, it is a relatively placid and slow-moving shark. This species has a sharp, pointy head, and a bulky body. The sand tiger's length can reach 3.0 to 3.4 meters (9.8 to 11.2 ft). They are grey with reddish-brown spots on their backs. The sand tiger prefers to hunt close to shore, and shivers (groups) have been observed to hunt large schools of fish. Their diet consists of bony fish, crustaceans, squid, and skates. Unlike other sharks, the sand tiger can gulp air from the surface, allowing it to be suspended in the water column with minimal effort. During pregnancy, the most developed embryo will feed upon its siblings,a reproductive strategy known as intrauterine cannibalism. The sand tiger is categorized as vulnerable on the International Union for Conservation of Nature Red List. It is the most widely kept shark in public aquariums owing to its large size and tolerance for captivity.
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The sand tiger shark's classification, Carcharias taurus, was originally determined by Rafinesque, a Turkish naturalist, after catching a specimen off the coast of Sicily. Its taxonomic classification has been long disputed by shark experts. Twenty-seven years after Rafinesque's original naming, Müller and Henle, German biologists, changed the genus name from C. taurus to Triglochis taurus. The following year, Swiss-American naturalist Jean Louis Rodolphe Agassiz reclassified the shark as Odontaspis cuspidata based upon examples of fossilized teeth. Agassiz's name was used until 1961 when three paleontologists and ichthyologists, W. Tucker, E. I. White, and N. B. Marshall, requested the shark be returned to the genus Carcharias. The experts' request was rejected and Odontaspis was approved by the International Code of Zoological Nomenclature (ICZN). When experts concluded that taurus belongs after Odontaspis, the name was changed to Odontaspis taurus. In 1977, a South African shark expert, Leonard J. V. Compagno, challenged the Odontaspis taurus name and substituted Eugomphodus, a somewhat unknown classification, for Odontaspis. Many taxonomists questioned his change stating there was not a significant difference between Odontaspis and Carcharias. After changing the name to Eugomphodus taurus, Compagno successfully advocated in establishing the sharks current classification as Carcharias taurus. Carcharias taurus means "a shark with sharp jagged teeth". The ICZN approved this name, and today the name is used among shark experts.[2]
The eyes of the sand tiger shark tend to be small, lacking eyelids, one of the shark's many distinct characteristics.[3] The head is rather pointy, as opposed to round, while the snout is flattened with a conical shape. Its body is stout and bulky and its mouth extends beyond the eyes. The sand tiger shark usually swims with its mouth open displaying three rows of protruding, smooth-edged, sharp-pointed teeth. Adult sharks tend to have reddish-brown spots scattered around their entire body.[3] Juvenile sand tiger sharks have yellow-brown spots on their bodies.[4] The sand tiger shark has a grey back and white underside. The males have grey claspers with white tips located on the underside of their body. The caudal fin is elongated and has a long upper lobe. They have two large, broad-based grey dorsal fins set back beyond the pectoral fins.[5] The pectoral fins are triangular, and the tail is almost one-third as long as the shark's head. The sand tiger's length on average can reach up to 3.0 to 3.4 meters (9.8 to 11.2 ft); they can weigh 159 kg (350 pounds).[6]
In August 2007, an albino specimen was photographed off South West Rocks, Australia.[7]
The sand tiger shark is an active night feeder.[8] It is the only shark known to gulp air and store it in the shark's stomach, allowing the shark to maintain near-neutral buoyancy which helps it to hunt motionlessly and quietly so as not to alert its prey.[9][8] The sand tiger shark has been observed to gather in hunting groups with other sand tiger sharks when preying upon large schools of fish.[10] The sand tiger shark also gathers in numbers when hunting large prey or when mating.[11] As the shark matures, it tends to eat larger prey including other sharks, dolphins, and swordfish. Biologists have observed that the shark will usually swallow its prey whole, which if the prey is too large can lead to health problems for the shark such as esophagus, heart, and liver damage.[12]
The diet of the sand tiger shark often consists of fish, young sharks, rays, crustaceans, and bluefin tuna trapped in nets. The sand tiger hunts a variety of fish along the Atlantic coast of North America, including skates, mackerel, menhaden, butterfish, flounder, weakfish, bonito, alewives, and silver hake.[13][14] However, the sand tiger prefers bony fish such as eels, mullets, and sea basses.[9]
People associate the sand tigers with having a vicious demeanor because their teeth protrude from their mouths when their jaws are closed, but they are generally not a threat to humans. Sand tigers roam the surf of the Atlantic coast, sometimes in close proximity to humans, but of 29 reported attacks, only two were fatal.[9] There have been only a few instances of unprovoked sand tiger shark attacks on humans.[15] Spearfishing may lead to aggressive behavior.[9] When the sharks become aggressive they tend to steal the fish or bait rather than attacking humans. Owing to its large size and docile temperament, the sand tiger is commonly displayed in aquariums around the world.[8]
Sand tiger sharks roam the epipelagic and mesopelagic regions of the ocean[9], sandy coastal waters, estuaries, shallow bays, and rocky or tropical reefs, at depths of up to 19 meters (62 ft). However, sand tiger sharks inhabiting even deeper depths have been recorded. Sand tiger sharks have only been seen in Canadian waters three times: in the Minas Basin of Nova Scotia; near St. Andrews, New Brunswick; and off Point Lepreau, New Brunswick. [16] The sand tiger shark can be found in the Atlantic, Pacific and Indian Oceans, and in the Mediterranean and Adriatic Seas.[9]
In the Western Atlantic Ocean, the sand tiger shark is found in coastal waters around from the Gulf of Maine to Florida, in the northern Gulf of Mexico around the Bahamas and Bermuda, and from southern Brazil to northern Argentina. The sand tiger shark is also found in the eastern Atlantic Ocean from the Mediterranean Sea to the Canary Islands, at the Cape Verde Islands, along the coasts of Senegal and Ghana, and from southern Nigeria to Cameroon. In the western Indian Ocean, the shark's habitat ranges from South Africa to southern Mozambique, but it does not live around Madagascar. The sand tiger shark has also been sighted in the Red Sea and may be found as far east as India. In the western Pacific, it has been sighted in the waters around the coasts of Japan and Australia, but not New Zealand.[1] The sand tiger dwells in warmer waters, and migrates according to its hemisphere's seasonal changes (south for the winter; north for the summer). When migrating, the species tends not to travel great distances.[17]
Males reach sexual maturity at about six to seven years old and approximately 1.8 meters (6 ft) in length. Females reach maturity when approximately 2 meters (7 ft) long at about nine to ten years of age.[3] Mating occurs around the months of March and April in the northern hemisphere.[3] During mating, the male sand tiger grasps the female's fins with his teeth. This can leave deep cuts that normally heal within a week. The male shark uses claspers (modified pelvic fins), to inseminate the female.[18] The sand tiger shark has one of the lowest reproduction rates of all species of sharks, therefore, they are easily affected by population pressures.[8] Female sharks have two uteri. During early embryonic stages the young absorb nutrients from a yolk sac and possibly consume uterine fluids. At approximately 10 centimeters (4 in) in length, developing embryos in the mother's uteri are killed and devoured by two surviving pups, a process called intrauterine cannibalism. There are reports of biologists probing the bellies of landed females and having their fingers nipped by the cannibalistic young with their fully developed teeth.[19] The surviving embryos (one in each uteri) continue to feed on a steady supply of yolk capsules that contain 7-23 unfertilized ova.[20] After a lengthy labour, the female gives birth to 1 meter (3 ft) long, fully independent offspring. The gestation period is approximately eight to nine months.[3] Hydroids grow on the mother's teeth during pregnancy because she stops feeding.[21]
This species is listed as vulnerable on the International Union for Conservation of Nature Red List,[1] and as endangered under Queensland's Nature Conservation Act 1992. It is a U.S. National Marine Fisheries Service Species of Concern, which are those species that the U.S. Government’s National Oceanic and Atmospheric Administration, National Marine Fisheries Service (NMFS), has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act. According to the National Marine Fisheries Service, any shark caught must be released immediately with minimal harm, and is considered a prohibited species, making it illegal to harvest any part of the sand tiger shark on the United States' Atlantic coast.[3] The population of the sand tiger has been reduced over twenty percent in the past ten years, which means the shark is considered vulnerable by the World Conservation Union. There are several factors contributing to the decline in the population of the sand tigers. Sand tigers can be caught by fishing trawls, although they are more commonly caught with a fishing line. Sand tigers' fins are a popular trade item in Japan.[1] Shark liver oil is a popular product in beauty products such as lipstick. [3] Thus, overfishing is a major contributor to the population decline. In northern Australia, nets are put in place to protect swimmers from sharks. Many sand tigers are caught in the nets, and then either strangled or taken by fishermen.[1] Estuaries along the United States of America's eastern Atlantic coast houses many of the young sand tiger sharks. These estuaries are susceptible to non-point source pollution that is harmful to the pups.[3]
Because the sand tiger is worldwide in distribution it has many common names. The grey nurse shark, the name used in Australia and the United Kingdom, is the second-most-used name for the shark. Other names include spotted ragged tooth (South Africa) and blue-nurse sand tiger (India).[22]
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