Borneo shark
The Borneo shark is a very rare and little-known 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, found in the shallow coastal waters of northwestern Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

 and possibly elsewhere in Southeast Asia. A small shark reaching 70 cm (27.6 in) in length, this species is the only member of its genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 with enlarged pores above the corners of its mouth. It has a slender body, colored gray above and white below, and a long, pointed snout. With only a handful of confirmed sightings and heavy fishing occurring within its range, the Borneo shark has been assessed as Endangered by the International Union for Conservation of Nature (IUCN).

Taxonomy and phylogeny

The Borneo shark was originally described as Carcharias (Prionodon) borneensis by Dutch ichthyologist Pieter Bleeker
Pieter Bleeker
Pieter Bleeker was a Dutch medical doctor and ichthyologist, famous for his work on the fishes of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877....

, in an 1858 issue of the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...

 Acta Societatis Regiae Scientiarum Indo-Neêrlandicae. He based his account on a 24 cm (9.4 in) long immature male caught off Singkawang
Singkawang is located at the province of West Kalimantan or Kalimantan Barat, Indonesia. It is located at about 145 km north of Pontianak, the provincial capital, and is surrounded by the Pasi, Poteng, and Sakok mountain...

, Borneo. Subsequent authors have recognized this shark as belonging to the genus Carcharhinus.

The evolutionary relationships of the Borneo shark 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 also containing the smalltail shark
Smalltail shark
The smalltail shark is a species of requiem shark, family Carcharhinidae, found in the western Atlantic Ocean from the northern Gulf of Mexico to southern Brazil. It inhabits shallow waters close to shore, particularly over muddy bottoms around estuaries. It tends to swim low in the water column...

 (C. porosus), blackspot shark
Blackspot shark
The blackspot shark, Carcharhinus sealei, is a requiem shark of the family Carcharhinidae, found in the Indo-West Pacific oceans between latitudes 24° N and 30° S, from the surface to 40 m. Its length is up to about 1.5 m....

 (C. sealei), spottail shark
Spottail shark
The spottail shark is a species of requiem shark, family Carcharhinidae, found in the Indo-West Pacific oceans waters between latitudes 31° N and 31° S, from the surface to 140 m. Its length is up to about 1.6 m....

 (C. sorrah), creek whaler
Creek whaler
The creek whaler, Carcharhinus fitzroyensis, is a requiem shark of the family Carcharhinidae, found in the southwestern Pacific Ocean between latitudes 10° S and 26° S, from the surface to at least 40 m. Its length is up to about 1.35 m....

 (C. fitzroyensis), whitecheek shark
Whitecheek shark
The whitecheek shark, Carcharhinus dussumieri, is a requiem shark of the family Carcharhinidae, found in the Indo-West Pacific Ocean between latitudes 34° N and 25° S. Its length is up to about 1.2 m....

 (C. dussumieri), hardnose shark
Hardnose shark
The hardnose shark is a species of requiem shark, family Carcharhinidae, found in the Indo-West Pacific oceans between latitudes 26° N and 11° S, from the surface to 170 m. Its length is up to about 1.1 m....

 (C. macloti), and Pondicherry shark
Pondicherry shark
The Pondicherry shark is a very rare and little-known species of requiem shark, family Carcharhinidae. It is mostly found in coastal and possibly brackish waters around the Indian subcontinent and Southeast Asia. This shark is small and stocky, with a rather long snout and a large first dorsal fin...

 (C. hemiodon). It also bears morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 similarities to Rhizoprionodon
Rhizoprionodon is a genus of requiem sharks, family Carcharhinidae, commonly known as sharpnose sharks because of their long, pointed snouts.-Species:* Rhizoprionodon acutus...

species, though it clearly belongs in Carcharhinus.

Distribution and habitat

All recent specimens of the Borneo shark have come solely from the shallow, inshore waters off Mukah
Mukah, Sarawak, Malaysia, is a coastal town which serves as the administrative center of the Mukah District in Mukah Division, Sarawak. It is located by the South China Sea, about 2.5 hours by road from the town of Sibu. Mukah is also accessible by air by MASwings from Kuching and Miri. The...

 in northwestern Borneo. Historically its range may have been wider, with two specimens known from Kalimantan
In English, the term Kalimantan refers to the Indonesian portion of the island of Borneo, while in Indonesian, the term "Kalimantan" refers to the whole island of Borneo....

 in the 1800s, one known from southern China in 1936, and unconfirmed records from the Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

 and Java
Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...



The Borneo shark is slim-bodied, with a long, pointed snout and oblique, slit-like nostrils preceded by narrow, nipple-shaped flaps of skin. The eyes are rather large and circular, and equipped with nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...

s (protective third eyelids). The corners of the sizable mouth bear short, indistinct furrows, and immediately above are a series of enlarged pores that are unique within the genus. There are 25–26 upper and 23–25 lower tooth rows. The upper teeth have a single narrow, oblique cusp with strongly serrated edges, and large cusplets on the trailing side. The lower teeth are similar, but tend to be more slender and finely serrated. 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 short.

The pectoral fins are short, pointed, and falcate (sickle-shaped), while the pelvic fins are small and triangular with a nearly straight trailing margin. 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 fairly large and triangular, with a blunt apex sloping down to a sinuous trailing margin; its origin lies over the free rear tips of the pectoral fins. The second dorsal fin is small and low, and originates over the middle of the anal fin base. There is no ridge between the dorsal fins. The caudal fin is narrow, with a well-developed lower lobe and a strong ventral notch near the tip of the upper lobe. The dermal denticles are small and overlapping, each with three horizontal ridges leading to marginal teeth. The Borneo shark is slate-gray above, darkening towards the tips of the dorsal fins and upper caudal fin lobe, and white below. There are faint, lighter edges on the pectoral, pelvic, and anal fins. The maximum known size is 70 cm (27.6 in).

Biology and ecology

Virtually nothing is known of the natural history of the Borneo shark. Like other members of its family, it is viviparous with the fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

es sustained by a placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

l connection. One recorded female contained six pups. Newborns measure around 24–28 cm (9.4–11 in) long; males mature at under 59 cm (23.2 in) long, and females at under 61 cm (24 in).

Human interactions

Until recently, only five confirmed specimens of the Borneo shark were known, all of them immature and collected before 1937. Several extensive surveys in the region since have failed to find it and the species was feared extinct, but in 2007 researchers from Universiti Malaysia Sabah
Universiti Malaysia Sabah
Universiti Malaysia Sabah or UMS is the ninth Malaysian public university located in Kota Kinabalu, Sabah, Malaysia and was established on November 24, 1994...

 rediscovered it during a survey of the fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

 resources of Sabah
Sabah is one of 13 member states of Malaysia. It is located on the northern portion of the island of Borneo. It is the second largest state in the country after Sarawak, which it borders on its southwest. It also shares a border with the province of East Kalimantan of Indonesia in the south...

 and Sarawak
Sarawak is one of two Malaysian states on the island of Borneo. Known as Bumi Kenyalang , Sarawak is situated on the north-west of the island. It is the largest state in Malaysia followed by Sabah, the second largest state located to the North- East.The administrative capital is Kuching, which...

. The Borneo shark is subject to heavy fishing pressure within its range, largely from the East Asian demand for fins
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...

, and it remains at high risk of extinction. The International Union for Conservation of Nature (IUCN) has listed it as Endangered.
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