sand tiger sharks Carcarias taurus ), gray shark nurse , spotted ragged tooth shark , or blue-nurse sand tiger is a shark species that inhabit subtropical and subtropical waters around the world. It inhabits the continental shelf, from the sandy shoreline (hence the name of the tiger shark) and submerged coral to a depth of about 191 m (627 ft). They live in the waters of Japan, Australia, South Africa, the Mediterranean and the east coast of North and South America. Despite its name, it is not associated with the tiger shark Galeocerdo cuvier ; However, it is the cousin of the great white shark Carcharodon carcharias .
Despite its scary appearance and strong swimming ability, it is a relatively quiet and slow-moving shark without any confirmed human casualties. This species has a sharp, pointed head, and a large body. Long tiger sand can reach 3.2 m (10.5 feet). They are gray with reddish-brown spots on their backs. Shivers (groups) have been observed to hunt down large schools of fish. Their diet consists of bony fish, crustaceans, squid, roller skates and other sharks. Unlike other sharks, the sand tiger can swallow air from the surface, allowing it to be hung in the water column with little effort. During pregnancy, the most developed embryo will feed its siblings, a reproductive strategy known as intrauterine cannibalism that is "embryophagy" or, more colorfully, adelphophagy - literally "eating a brother". Sand tigers are categorized as vulnerable to the International Red List of Nature Conservation. This is the largest shark most kept in a public aquarium because of its tolerance to captivity.
Video Sand tiger shark
Taxonomy
Description of the tiger sand tiger as Carcharias taurus by Constantine Rafinesque comes from specimens captured off the coast of Sicily. Carcharias taurus means "bull shark". This taxonomic classification has long been disputed. Twenty-seven years after the original descriptions of Rafinesque, German biologists, MÃÆ'¼ller and Henle renamed the genus from C. taurus to Triglochis taurus . The following year, Swiss-American naturalist Jean Louis Rodolphe Agassiz reclassified sharks as Odontaspis cuspidata based on the example of dental fossils. The name Agassiz was used until 1961 when three paleontologists and ichthyologists, W. Tucker, E. I. White, and N. B. Marshall, requested that the sharks be returned to the genus Carcharias . This request was rejected and Odontaspis was approved by the International Code of Zoological Nomenclature (ICZN). When experts conclude that the taurus belongs after Odontaspis , the name is changed to Odontaspis taurus . In 1977, Compagno and Follet challenged the name of Odontaspis taurus and replaced Eugomphodus, a rather unknown classification for Odontaspis . Many taxonomists question the change, arguing that there is no significant difference between Odontaspis and Carcharias . After changing the name to Eugomphodus taurus , Compagno successfully advocated setting the current scientific name of the shark as Carcharias taurus . ICZN approves this name, and is used today among biologists.
Maps Sand tiger shark
Common names
Because sand tiger sharks are scattered all over the world, it has many common names. The term "sand tiger shark" actually refers to four different species of tiger sharks in the family of Odontaspididae. Furthermore, the name creates confusion with the tiger shark Galeocerdo cuvier , which is not associated with a sand tiger. The gray shark nurse , the name used in Australia and the UK, is the second most commonly used name for sharks, and in India it is known as the blue-nurse sand tiger . However, there are unrelated nurse sharks in the Ginglymostomatidae family. The least ambiguous and descriptive English name is probably one of South Africans,
Identify
There are four species of sand tiger sharks
- Sand tiger shark Carcharias taurus
- Indian sand tiger shark Carcharias tricuspidatus . Very little is known about this species, described before 1900, probably equal to (similar to) the tiger sand C. taurus
- Tiger shark's small toothed shark Odontaspis ferox . This species has a worldwide distribution, is rarely seen but usually inhabits deeper water than C. taurus .
- The large-eyed tiger shark Odontaspis noronhai , the deep water shark from America, is little known.
The most probable problem when identifying a sand tiger shark is when in the presence of one of two species of Odontaspis . First, the sand tiger is usually seen, especially in the back of the body. However, there are some other differences that may be more reliable:
- The bottom of the tail fin (tail fin) of the smaller sand tiger;
- The second dorsal fin (back) of the sand tiger is almost as large as the first dorsal fin (ie the front).
- The first dorsal fin (front) of the sand tiger is relatively asymmetrical;
- The first dorsal dorsal (front) fin of the sand tiger is closer to the abdominal fin than the pectoral fin (ie the first dorsal fin is positioned further back in the case of the sand tiger);
Description
Adult tigers range from 2 m (6.6 feet) to 3.2 m (10.5 feet) and 91 kg (200.6 kg) to 159 kg (350.5 pounds) by weight. The head is pointed, not round, while the muzzle is flat with a conical shape. His body was thick and bulky and his mouth widened beyond the eyes. Tiger shark eyes are small, lacking eyelids. A sand tiger usually swims with open mouth displaying three rows of protruding, sharp-pointed, sharp-pointed teeth. Males have gray claspers with white tips located at the bottom of their bodies. The tail fins are elongated with long upper lobes (ie very heterocercal). They have two large gray wide dorsal fins located behind the pectoral fins. The sand tiger shark has a grayish gray back and a pale bottom. Adults tend to have reddish brown spots that are scattered, mostly at the back of the body. In August 2007, an albino specimen was photographed from South West Rocks, Australia. This shark's teeth do not have transverse serrations (as have many other sharks) but they have large, smooth main cusps with small cusplets on each side of the main cusp. The upper front teeth are separated from the teeth at the side of the mouth by a small intermediate tooth.
Habitat and range
Geographic range
Tiger sharks roam the epicagis and mesopelagic areas of the ocean, sandy beach waters, estuaries, shallow bays and rocky or tropical corals, at a depth of up to 190 meters (623 feet).
Tiger sharks can be found in the Atlantic, Pacific and Indian Oceans, and in the Mediterranean Sea and the Adriatic Sea. In the Western Atlantic Ocean, it 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. It is also found in the eastern Atlantic Ocean from the Mediterranean Sea to the Canary Islands, in the Cape Verde Islands, along the coasts of Senegal and Ghana, and from southern Nigeria to Cameroon. In the western Indian Ocean, sharks range from South Africa to southern Mozambique, but exclude Madagascar. Sea tiger sharks have also been seen in the Red Sea and can be found in the east as far as India. In the western Pacific, it has been seen in the waters around the coast of Japan and Australia, but not in New Zealand.
Yearly migration
Sand tigers in South Africa and Australia carry out an annual migration that may cover more than 1,000 km (620 mi). They pup during summer in relatively cold water (temperatures around 16Ã, Â ° C). After the birth process, they swim north to a location where there are rocks or caves that match, often in the depths of the water. 20 m (66 ft), where they mate during and right after winter. Mating usually occurs at night. After mating, they swim further north even to the warmer water where the pregnancy occurs. In Autumn they return south to give birth in cold water. This round trip can cover up to 3,000 km (1,900 mi). Young sharks do not take part in this migration, but they are absent from normal birthplace during the winter: it is estimated that they move further into the sea. In Cape Cod (USA), adolescents migrate from coastal areas when water temperatures drop below 16 ° C (61 ° F) and day length decreases to less than 12 hours. Teenagers, however, return to their usual haunted summers and as they mature they begin a larger migration movement.
Behavior
Hunting
The sand tiger shark is a nocturnal feeder. During the day, they take shelter near rocks, overhangs, caves and corals often at relatively shallow depths (& lt; 20 m). This is a typical environment where divers are facing a sand tiger, hovering just above the bottom in a big sandy ditch and cave. However, at night they leave the shelters and hunt on the seabed, often far apart from their shelter. Sand tigers hunt in secret. It is the only known shark to swallow air and store it in the shark's belly, allowing sharks to retain almost neutral buoyancy that helps to hunt without moving and quietly. Aquarium observations show that when it comes close enough to the prey item, it catches with a quick side snap. Tiger sand sharks have been observed to gather in hunting groups when targeting large schools of fish.
Diet
The majority of prey items from sand tigers are demersal (ie from the seafloor), indicating that they are hunting extensively on the seafloas as far as the continental shelf. Reinforced fish (Teleosts) make up about 60% of the sand tiger food, the remaining prey consisting of sharks and rollerblading. In Argentina, prey includes most demersal fish, eg. weakly lined fish ( Cynoscion guatucupa ). The most important elasmobranch is the bottom hunter shark shark ( Mustelus sp. ). Benthic rays (ie free swimming) and roller skates are also taken. Stomach contents analysis showed that smaller sand tigers mainly focus on the seafloor and as they grow larger they begin to pick up more benthic prey. The perspectives of the sand tiger diet are consistent with similar observations in the northwest Atlantic and in South Africa where large tigers capture more species of sharks and skates as prey, from the surf zone to the continental shelf, indicating the opportunistic nature of feeding the sand tiger. Outside South Africa, a sand tiger of less than 2 m (6 ft 7 inches) in length feeds on a fish about a quarter of its own length; However, large sand tigers capture prey to half of its length. Prey items are usually swallowed as three or four pieces.
Dating and mating
The marriage takes place around March and April in the northern hemisphere and during August-October in the southern hemisphere. The dating and marriage of the tiger sand has been well documented from observations in large aquariums. At Oceanworld, Sydney, females tend to drift slightly above the sandy bottom ("protect") when they receive. This prevents men from approaching down to their cloaca. Often there is more than one male close to the dominant one remaining close to the woman, intimidating others with an aggressive look in which the dominant shark follows the subordinate's tail, forcing subordinates to accelerate and swim away. Male superior is dominant in smaller fish than other species. Men approaching women and two sharks protect the sandy bottom where they interact. The strong interest of men is indicated by the shallow bites in the female rectal and pectoral areas. The female responds by biting the man superficially. This behavior continued for several days in which the men patrolled the area around the female. Men regularly approach women in "nosing" behaviors to "kiss" female cloaca. If he is ready, he swims with the men, while the two spins twist their bodies so that the male right-hand jaw enters the female cloaca. The man bites the base of his right breast fin, leaving a scratch that is easily visible afterwards. After a minute or two, the marriage is complete and the two are separated. Women often mate with more than one man. Women marry only every second or third year. After mating, females remain behind, while the males move in search of other areas to feed, resulting in many observations of a population of sand tigers made up almost exclusively by females.
Reproduction and growth
Reproduction
The pattern of reproduction is similar to many of Lamnidae, the shark family owned by tigers of sand. Female tigers have two uterine horns that, during early embryonic development, may have as many as 50 embryos that obtain nutrients from their yolk sac and may consume uterine fluids. When one embryo reaches about 10 cm (4 inches) in length, it feeds all the smaller embryos so that only one large embryo is left in each uterine horn, a process called intrauterine cannibalism that is "embryophagy" or, more colorfully, adelphophagy - - literally "eat someone's brother." While many male sand tigers generally fertilize single females, adelphophagy sometimes excludes all but one of them gets offspring. The surviving embryo continues to feed on infertile supply of eggs. After a long labor, the females give birth to 1 m (3 ft) long, fully independent offspring. The pregnancy period is about eight to twelve months. These sharks only give birth every second or third year, resulting in an average overall reproductive rate of less than one child per year, one of the lowest reproductive rates for sharks.
Growth
In the north Atlantic, sand tiger sharks are born about 1 m in length. During the first year, they grow about 27 cm till it reaches 1.3 m. Thereafter, the growth rate decreases by about 2.5 cm each year until it stabilizes at about 7 cm/y. Men reach sexual maturity at the age of five to seven years and about 1.9 m (6 ft) in length. Women reach maturity when about 2.2 m (7 feet) long in about seven to ten years. They are usually not expected to reach lengths longer than 3 m. In the informal media, like YouTube, there are reports of tigers about 5m long, but none are scientifically verified.
Interaction with humans
Attack on humans
Sand tigers are often associated with demons or deadly, because of their relatively large and sharp size, teeth protruding from their jaws; However, this shark is quite tame, and not a threat to humans. Their mouths are not large enough to cause human deaths. Sand tigers roam the waves, sometimes close to humans, and there are only a few examples of unprovoked tiger shark attacks on humans, usually associated with spear fishing, in-line fishing, or feeding sharks. In 2013, the Shark Attack Rescue database did not include any casualties due to sand tiger sharks. When sharks become aggressive, they tend to steal fish or bait from fishing lines rather than attack humans. Due to its large size and benign temperament, sand tigers are usually displayed in aquariums around the world.
Nets around the swimming beach
In Australia and South Africa, one common practice in coastal vacation areas is to establish shark nets around beaches that are often used by swimmers. The net was erected about 400 m (1,300 ft) from the shore and acts as a gill net that entraps incoming sharks: this is the norm until around 2005. In South Africa, the mortality of sand tiger sharks causes a significant reduction in the length of these animals and it was concluded that shark nets pose a significant threat to this species with very low reproductive rates. Before 2000, this net claimed about 200 sand tiger sharks per year in South Africa, of which only about 40% survived and were released alive. The efficiency of shark nets for unwarranted shark attack prevention has been questioned, and since 2000 there has been a reduction in the use of these nets and alternative approaches are being developed.
Competition for food with humans
In Argentina, prey goods from sand tigers largely coincide with important commercial fishing targets. Humans affect the availability of food tiger sand and sharks, in turn, compete with humans for food which, in turn, has been greatly exploited by the fishing industry. The same is true for lower-sea catfish ( Galeichthys feliceps ), fisheries resources off the coast of South Africa.
The effects of scuba divers
Sand tiger sharks are often the target of divers who want to observe or photograph these animals. A study near Sydney in Australia found that shark behavior is influenced by the proximity of scuba divers. The activity of divers affects aggregation behavior, swimming, and shark breathing, but only on short time scales. The size of the scuba divers group is less important in influencing the tiger's sand behavior than the distance at which they approach the shark. Divers that approached in 3 m sharks affect their behavior but after the diver retreats, the sharks return to normal behavior. Other studies show that the Sand Tiger can become indifferent to divers. Scuba divers are usually obedient when it comes to observing Australian regulations for shark diving. In North America, shipwreck World War II ships off the coast of North Carolina provides habitat for sharks and opportunities for close encounters between sharks and divers.
In captivity
Its large and threatening appearance, combined with its relative calmness, has made sand tiger sharks among the most popular shark species featured in public aquariums. However, as with all the big sharks, keeping them in captivity is not without difficulty. The sand tiger shark has been found to be particularly vulnerable to developing spinal deformities, with as many as one out of every three affected prisoners, giving them a hunchback appearance. This deformity has been hypothesized to correlate with the size and shape of their tank. If the tank is too small, the sharks have to spend more time active swimming than in the wild, where they have room to glide. In addition, sharks in small round tanks often spend most of their time circling along the edges in only one direction, causing asymmetrical pressure on their bodies.
Conservation threat and status
Threat
There are several factors that contribute to the decline of the tiger sand populations. Sand tigers reproduce at an unbelievably low rate, due to the fact that they do not have more than two children at once and because they breed only every second or third year. These sharks are invaluable foods in the northern western Pacific, off the coast of Ghana and off India and Pakistan where they are caught by trawlers, although they are more often caught with fishing rods. Tiger sand fin is a popular trading item in Japan. Outside North America, this fish is taken for the skin and fins. Shark liver oil is a popular product in cosmetic products such as lipstick. This is sought by anglers in fishing competitions in South Africa and some other countries. In Australia, the number has been reduced by spear fishermen who use toxins and are now protected. It is also appreciated as an aquarium exhibit in the United States, Europe, Australia and South Africa due to its docile and strong nature. Thus, overfishing is a major contributor to population decline. All indications show that the world's population in tigers has been significantly reduced in size since 1980. Many sand tigers are caught in shark nets, and then strangled or taken by fishermen. Estuary along the eastern Atlantic coast of the United States home of many young sand tiger sharks. The estuary is vulnerable to pollution of non-point sources that are harmful to puppies.
Conservation status
The species is therefore listed as vulnerable to the International Red List of Nature Conservation, and as endangered under the Queensland Nature Conservation Act 1992. This is the US National Fisheries Service. [Caring Species] , which is a species provided by the US Marine Administration's National Marine Fisheries Service (NMFS), has some concerns about status and threats, but insufficient information is available to show the need to list species under the US Species Species Act. According to the National Marine Fisheries Service, every shark captured must be immediately released with little damage, and is considered a forbidden species, making it illegal to harvest any part of the tiger sand sharks on the Atlantic coast of the United States.
A recent PEW Charitable Trusts report suggests that a new management approach used for large mammals that have already declined in population can be promising for sharks. Because of the shark life characteristics, conventional fisheries management approaches, such as achieving maximum sustainable yields, may not be sufficient to rebuild a depleted shark population. Some of the more rigorous approaches used to reverse the decline in large mammals may be suitable for sharks, including restrictions on retention of the most vulnerable species and international trade regulation.
References
Bibliography
External links
- The tangled taxonomic history of the sand tiger shark - Additional taxonomic information
- Carcharias taurus , Tiger shark from FishBase
- The Tiger Shark Sand School
- Species Description of Carcharias taurus at www.shark-references.com
- Tiger Shark Sand
- Shark Info
- Scuba divers swimming between sharks
Source of the article : Wikipedia
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