Sharp-toothed sand shark

For the first time, the species was scientifically described under the name Squalus ferox by the Italian-French naturalist Antoine Rissot in 1810 on the basis of a specimen caught off the coast of Nice, France ^[2] . In 1950, Gilbert Percy Whiteley based on an Australian sample, described Odontaspis herbsti separately from Odontaspis ferox , justifying this by differences in teeth and lack of stains. In 1984, Leonard Compagno synonymous these two names ^[3] . The name of the genus comes from the words Greek. ὀδούς - “tooth” and Greek. ασπιδος - “shield” ^[4] , and the specific name from the word lat. ferox - "ferocious."

Phylogenetic studies based on mitochondrial DNA have established that a sharp-toothed sand shark and a closely related species of large-eyed sand shark are associated more with fox sharks than with an ordinary sand shark , which they are very similar in appearance. In fact, this may indicate that the similarity arose as a result of convergent evolution ^[5] .

The fossilized teeth of a sharp-toothed sand shark found in Italy and Venezuela belong to the Lower Pliocene period (5.3–3.6 million years ago) ^[6] - ^[7] .

The sharp-toothed sand sharks live in almost all tropical seas and warm temperate waters. In the Western Atlantic, they are found off the coast of Mexico ( Bank of Campache ), USA ( North Carolina ) and Brazil. In the East Atlantic, they live in the Bay of Biscay , off the coast of Madeira , Morocco , Western Sahara, and in the Mediterranean Sea . In the Indian Ocean, they can be found from South Africa ( Kwazulu-Natal ) to Madagascar , as well as the Maldives, Sri Lanka , Sumatra and the northern coast of Australia . In the eastern part of the Pacific Ocean, these sharks are observed in the waters of Japan, Australia ( New South Wales ), New Zealand and near the island arc Kermadek . In the central part of the Pacific Ocean, they live off the coast of Hawaii , and in the western part - the USA (southern California ), Mexico ( Gulf of Mexico and Baja California ) and Colombia ( Malpelo Island ) ^[8] .

Usually sharp-toothed sand sharks are found at a depth of up to 880 m. Usually they stay at the bottom along which stone boulders are scattered, on the continental shelf or in the upper part of the continental slope. These sharks are sometimes found near a cliff on rocky or coral reefs , as well as around seamounts and ridges. In the Mediterranean Sea, sharp-toothed sand sharks are observed at a depth of up to 250 m, including the depths available to divers ^[3] . The preferred temperature range is from 6 to 20 ° C. In hot climates, they are kept under a thermal wedge, where the water is cooler ^[3] .

The sharp-toothed sand sharks have a stocky body with a long head and a slightly flattened snout. Eyes of medium size with a large round pupil, in contrast to the slit-like pupils of ordinary sand sharks. The third eyelid is absent. Each tooth is equipped with a long central tip and 2-3 lateral teeth. On the upper jaw 46–48, and on the lower 36–46 dentitions ^[8] . The bases of the dorsal fins are wide, the fins themselves are rounded. The first dorsal fin is larger than the second, shifted backward; its base is closer to the base of the pectoral than the ventral fins. The anal fin is the same or larger than the dorsal fins. The caudal fin is asymmetrical; the upper lobe is much longer than the lower. There are no lateral carinae on the caudal stem. There is a precaudal notch on the caudal peduncle. The height of the anal fin is from 4.6 to 6% of the total body length. The trailing edge is bent. ^[8] .

Coloring is gray or gray-brown, light belly. Some individuals have dull spots on their sides. In young sharks, the edges of the fins are slightly darker than the main color ^[8] .

The maximum recorded length is 450 cm and the weight is 289 kg ^[9] .

The sharp-toothed sand sharks are active predators. They are found both in small flocks, and individually. Probably, they are able to overcome long distances, following along underwater ridges ^[3] . They have a very large liver with a high fat content, which allows them to maintain neutral buoyancy in the water column with minimal effort. Along the shores of Beirut , Lebanon , at a depth of 30–45 m there is an area where sharp-toothed sand sharks sail every year in the summer ^[10] . Some individuals return to the same place from year to year ^[3] . The purpose of these migrations is unknown, probably mating. Adult sharp-toothed sand sharks have no enemies in natural conditions. Lithobothrium gracile tapeworms are parasitic on them, and Brazilian luminous sharks can be a predator.

Little is known about the breeding of sharp-toothed sand sharks. So far, not a single pregnant female has been caught. A female from the Gulf of California is described, the right ovary of which was full of small eggs. Probably, like other lamellar, these sharks reproduce by oviparous birth with oophagy ^[8] . The size of newborns is 1-1.1 m. Young sharks are kept at a greater depth compared to adults. Probably, in this way they avoid meeting with large predators that live in shallow water, for example, with a white shark .

Males reach puberty when they reach a length of 2–2.5 m, and females 3–3.5 m. Scars on the bodies of some individuals can be obtained during courtship ^{[3] [8]} .

Compared to ordinary sand sharks, sharp-toothed sand sharks have a not so impressive set of teeth adapted to tear and crush, which suggests that they prey on relatively small prey ^[8] . They feed on bony fish , for example, sea ​​bass , invertebrates, including squid , isopods, crustaceans and cartilaginous fish ( stingrays and chimeras ). The largest recorded prey of a sharp-toothed sand shark was a black shark 1.3 m long, found in the stomach of a male 2.9 m long off the coast of New Caledonia ^[3] .

The shark as a whole is considered non-aggressive, numerous divers who have seen these sharks under water indicate that they are timid and do not show aggression, even when they are approached for a short distance ^[8] . They by-catch gillnets, bottom trawls and longlines, especially in the Mediterranean Sea and off the coast of Japan. As a rule, they are thrown overboard, with the exception of Japan, where meat is eaten, although it is considered low-grade compared to the meat of ordinary sand sharks ^[8] . In addition, fins, jaws and cartilage are appreciated ^[9] .

In the early 1970s, sharp-toothed sand sharks were discovered in shallow water. This discovery raised concern about the ability of this species to withstand anthropogenic impact . There is insufficient data to assess conservation status around the world, however, in Australian waters, the International Union for Conservation of Nature has assigned this species a “Vulnerable” status due to a 50% reduction in the production of these sharks off the coast of New South Wales since the 1970s. It is believed that the size of the Mediterranean population has also declined due to the deterioration of habitat, overfishing , pollution and human impact ^[11] . In Australia, sharp-toothed sand sharks have been under state protection since 1984, but it is currently difficult to assess the effectiveness of these measures ^[3] .