Borneo shark
Rare requiem shark with unique mouth pores, found only off northwestern Borneo.
The Borneo shark (Carcharhinus borneensis) is a type of requiem shark belonging to the family Carcharhinidae. This extremely rare animal has only been found in shallow coastal waters near Mukah, on the northwestern coast of Borneo, although it may have lived across a broader area in the past. A small, gray shark that grows to 65 centimeters (26 inches) in length, it stands out as the only species in its genus that has a distinct row of enlarged pores just above the corners of its mouth. Its body is slender, with a long, pointed snout and a low second dorsal fin that sits behind the start of the anal fin.
Very little is known about the Borneo shark’s life history. Like other requiem sharks, it gives birth to live young, with females producing litters of six pups that develop inside the mother through a placental connection. The International Union for Conservation of Nature last classified this species as Critically Endangered. Although a living population has since been confirmed, the shark remains a conservation concern because its range is extremely limited and lies within waters that are heavily fished.
**Taxonomy and phylogeny** The Borneo shark was first described by Dutch ichthyologist Pieter Bleeker in 1858, based on a newborn male just 24 centimeters (9.4 inches) long that was caught off Singkawang in western Kalimantan, Borneo. He named it *Carcharias (Prionodon) borneensis* in the journal *Acta Societatis Regiae Scientiarum Indo-Neêrlandicae*. Later scientists placed it in the genus *Carcharhinus*. Before 2004, only five specimens—all immature and collected before 1937—were known. In April and May of that year, researchers from Universiti Malaysia Sabah found several more specimens while surveying fisheries in Sabah and Sarawak.
The evolutionary relationships of the Borneo shark remain unclear. In a 1982 morphological study, Jack Garrick did not link it closely to any other *Carcharhinus* species. Leonard Compagno, in 1988, tentatively grouped it with the smalltail shark, blackspot shark, spottail shark, creek whaler, whitecheek shark, hardnose shark, and Pondicherry shark. The Borneo shark shares certain traits with sharpnose sharks (*Rhizoprionodon*), such as the enlarged pores near its mouth, but other features of its body firmly place it within *Carcharhinus*.
Quick Facts
- Genus
- Carcharhinus
- Species
- borneensis
Facts from the source article.
Lore & Background
Dutch ichthyologist Pieter Bleeker originally described the Borneo shark as Carcharias (Prionodon) borneensis in an 1858 issue of the scientific journal Acta Societatis Regiae Scientiarum Indo-Neêrlandicae, based on a newborn male 24 cm long caught off Singkawang in western Kalimantan, Borneo. Before 2004, only five specimens were known, all immature and collected before 1937. In April and May 2004, researchers from Universiti Malaysia Sabah discovered additional specimens while surveying fishery resources of Sabah and Sarawak.
The Borneo shark is slim-bodied with a long, pointed snout and oblique, slit-like nostrils. It has a row of enlarged pores above the corners of its mouth, unique within the genus. The first dorsal fin is fairly large and triangular, while the second dorsal fin is small and low, originating over the middle of the anal fin base. The species is slate-gray above, darkening towards the tips of the dorsal fins and upper caudal fin lobe, with a white underside. The largest known specimen measures 65 cm long.
All recent specimens have been collected solely from fishery landing sites at Mukah in Sarawak, despite thorough surveys across the rest of Borneo. Its range may now be restricted to shallow, inshore waters in northwestern Borneo. Fossils are known from as early as the Late Miocene, found at Ambug Hill in Brunei alongside remains of blacktip sharks and other genera.
Reader's Guide
The Borneo shark is assessed as Critically Endangered by the International Union for Conservation of Nature. Although an extant population has since been found, the species continues to merit conservation concern given its highly limited range within heavily fished waters. It is caught by line gear and used for meat, though it has minimal commercial significance. The evolutionary relationships of the Borneo shark are uncertain; Jack Garrick in his 1982 morphological study did not place it close to any other member of the genus, while Leonard Compagno in 1988 tentatively grouped it with several other requiem sharks. The Borneo shark resembles sharpnose sharks in certain traits, such as the enlarged pores by its mouth, but other aspects of its morphology firmly place it within Carcharhinus. Its conservation status remains precarious due to its very small range in waters subjected to intensive artisanal and commercial fishing.
Did You Know?
- The Borneo shark is the only member of the genus Carcharhinus with a row of enlarged pores above the corners of its mouth.
- Only five specimens were known before 2004, all immature and collected before 1937.
- The largest known Borneo shark measures 65 cm (26 in) long.
- Fossils of the Borneo shark are known from as early as the Late Miocene.
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