Smooth tooth blacktip shark
Encyclopedia
The smoothtooth blacktip shark (Carcharhinus leiodon) is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...

, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Carcharhinidae, known only from a single 75 cm (29.5 in) immature specimen from the Gulf of Aden
Gulf of Aden
The Gulf of Aden is located in the Arabian Sea between Yemen, on the south coast of the Arabian Peninsula, and Somalia in the Horn of Africa. In the northwest, it connects with the Red Sea through the Bab-el-Mandeb strait, which is about 20 miles wide....

. It resembles the blacktip reef shark
Blacktip reef shark
The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...

 (C. melanopterus) in shape and color, having black tips on all fins, but has a more pointed snout and narrow, smooth-edged teeth in both jaws. Its natural history is unknown. The International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...

 on the basis of its small range.

Taxonomy and phylogeny

The sole specimen of the smoothtooth blacktip shark was an immature male caught by Wilhelm Hein in 1902, and scientifically described by New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 ichthyologist Jack Garrick in a 1985 National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 (NOAA) Technical Report. He gave it the specific epithet leiodon, from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 leios meaning "smooth", and odon meaning "tooth". Like many Carcharhinus species, the evolutionary relationships of this species are uncertain. In 1988, Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...

 placed it in an informal phenetic group with the spinner shark
Spinner shark
The spinner shark is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean...

 (C. brevipinna), blacktip shark
Blacktip shark
The blacktip shark is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean...

 (C. limbatus), graceful shark
Graceful shark
The graceful shark or Queensland shark is a species of requiem shark, family Carcharhinidae, found in the tropical Indo-Pacific from the Gulf of Aden to northern Australia. It is a midwater species that has been recorded to a depth of...

 (C. amblyrhynchoides), and the finetooth shark
Finetooth shark
The finetooth shark is a species of requiem shark, family Carcharhinidae, found in the western Atlantic Ocean from North Carolina to Brazil. It forms large schools in shallow, coastal waters and migrates seasonally following warm water...

 (C. isodon). However, the affinity between the spinner, blacktip, and finetooth sharks have been refuted by later molecular phylogenetic techniques.

Distribution and habitat

The locality of the sole specimen was given as the Gulf of Aden
Gulf of Aden
The Gulf of Aden is located in the Arabian Sea between Yemen, on the south coast of the Arabian Peninsula, and Somalia in the Horn of Africa. In the northwest, it connects with the Red Sea through the Bab-el-Mandeb strait, which is about 20 miles wide....

 near "Gischin", which likely refers to the town of Qishn
Qishn
Qishn is a coastal town in Al Mahrah Governorate, southern Yemen. It is located at around . Its population is estimated at more than 80000. It has a landing strip, which is currently not in use....

 in eastern Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....

. It was probably taken close to shore.

Description

Superficially, the smoothtooth blacktip shark resembles a blacktip reef shark
Blacktip reef shark
The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...

 (C. melanopterus) with a more pointed snout and different dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...

. It has 16 tooth rows on either side of the upper jaw and 15 tooth rows on either side of the lower jaw, along with three small teeth at the upper and lower symphyses (center). The teeth have narrow, erect cusps, and lack serrations; finetooth shark
Finetooth shark
The finetooth shark is a species of requiem shark, family Carcharhinidae, found in the western Atlantic Ocean from North Carolina to Brazil. It forms large schools in shallow, coastal waters and migrates seasonally following warm water...

s (C. isodon) and juvenile spinner shark
Spinner shark
The spinner shark is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean...

s (C. brevipinna) are the only other representatives in the genus with similar upper teeth. The nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

s are slit-like and preceded by small, pointed flaps of skin. The five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...

s are fairly long.

The pectoral fins are rather short, pointed, and slightly falcate (sickle-shaped), originating between the fourth and fifth gill slits. The first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 is medium-sized with a pointed apex, and originates over the posterior half of the inner pectoral fin margin. The second dorsal fin and anal fins are relatively large and placed about opposite each other. There is no mid-dorsal ridge between the dorsal fins. The dermal denticles are oval and slightly overlapping, with three prominent horizontal ridges leading to three or five marginal teeth. The color of the preserved specimen is yellowish-brown above and lighter below, which extends in a pale band onto the flanks. All fins have clearly delineated black tips, which extend to the entire trailing margin on the caudal fin. The specimen is 75 cm (29.5 in) long.

Biology and ecology

Nothing is known of the smoothtooth blacktip shark's history. It is presumably viviparous like other members of its family.

Human interactions

Because of its apparently restricted range in heavily fished waters and small population, the International Union for Conservation of Nature (IUCN) has assessed the smoothtooth blacktip shark as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...

. It is likely caught locally as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

.
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