Sand tiger shark

Appearance

The eyes of the sand tiger shark are small, lacking eyelids, one of the shark's many distinct characteristics. 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. Juvenile sand tiger sharks have yellow-brown spots on their bodies. 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. The pectoral fins are triangular, and the tail is almost one-third as long as the shark's head. The sand tiger's length at sexual maturity averages 1.9 to 1.95 m in males and 2.2 m in females, the latter being the larger-bodied sex. Large mature specimens can attain a length of 3.0 to 3.4 meters . A specimen of 50 kg in weight is considered "medium"-sized while a 95 to 110 kg specimen is considered "average"-sized. Sand tiger sharks have been reported to attain a maximum mass of 159 kg , however some sources claim the specimen can attain a weight of 300 kg .

In August 2007, an albino specimen was photographed off South West Rocks, Australia.

Naming

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'' and ''blue-nurse sand tiger'' .

Status

This species is listed as ''vulnerable'' on the International Union for Conservation of Nature Red List, 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 , 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. 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. Shark liver oil is a popular product in beauty products such as lipstick. 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. 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.

Behavior

The sand tiger shark is an active night feeder. 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. The sand tiger shark has been observed to gather in hunting groups with other sand tiger sharks when preying upon large schools of fish. The sand tiger shark also gathers in numbers when hunting large prey or when mating. 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.

Habitat

Sand tiger sharks roam the epipelagic and mesopelagic r the ocean, sandy coastal waters, estuaries, shallow bays, and rocky or tropical reefs, at depths of up to 19 meters . 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.
The sand tiger shark can be found in the Atlantic, Pacific and Indian Oceans, and in the Mediterranean and Adriatic Seas.

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. The sand tiger dwells in warmer waters, and migrates according to its hemisphere's seasonal changes . When migrating, the species tends not to travel great distances.

Reproduction

Males reach sexual maturity at about six to seven years old and approximately 1.8 meters in length. Females reach maturity when approximately 2 meters long at about nine to ten years of age. Mating occurs around the months of March and April in the northern hemisphere. 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 , to inseminate the female. The sand tiger shark has one of the lowest reproduction rates of all species of sharks, therefore, they are easily affected by population pressures. 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 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. The surviving embryos continue to feed on a steady supply of yolk capsules that contain 7-23 unfertilized ova. After a lengthy labour, the female gives birth to 1 meter long, fully independent offspring. The gestation period is approximately eight to nine months. Hydroids grow on the mother's teeth during pregnancy because she stops feeding.

Food

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 mackerel, menhaden, butterfish, flounder, weakfish, bonito, alewives, and silver hake. However, the sand tiger prefers bony fish such as eels, mullets, and sea basses.