Ганговая акула: Критически исчезающий вид и пересмотр таксономии.

Species of shark

The Ganges shark (Glyphis gangeticus) is a critically endangered species of requiem shark found in the Ganges River (Padma River) and the Brahmaputra River of India and Bangladesh. It is often confused with the more common bull shark (Carcharhinus leucas), which also inhabits the Ganges River and is sometimes incorrectly referred to as the Ganges shark. The genus is currently considered to contain three recent species; genetic evidence has shown that both the Borneo river shark (G. fowlerae) and Irrawaddy river shark (G. siamensis) should be regarded as synonyms of the Ganges shark, expanding the range of the species to Pakistan, Myanmar, Borneo, and Java. While the other members of the genus Glyphis occur in coastal marine waters as well as rivers, the Ganges shark is found only in fresh water, making it the world's only exclusively freshwater shark. The species remains poorly known and very rare.

Formerly the Borneo river shark (Glyphis fowlerae) and the Irrawaddy river shark (Glyphis siamensis) were considered to represent two other species in the genus Glyphis. They have recently been reclassified as G. gangeticus based on genetic studies, and their scientific names are treated as synonyms. The Borneo river shark is known only from the Kinabatangan River in Borneo. It can reach a length of Only 13 specimens are known to science, all collected in 1996. Expeditions in 2010 and 2011 failed to find any, and while fishermen recognised the shark, they have not been seen for many years. However, subsequent authors doubted the validity of this species, regarding it as an abnormal bull shark (Carcharhinus leucas), until in 2005 shark systematist Leonard Compagno recognized it as distinct member of the genus Glyphis. A possibly undescribed species of Glyphis is known from Mukah in Borneo, as well as Bangladesh. The status of a Borneo specimen from Sampit remains unclear. Its size at birth is , growing to an estimated at maturity, with a maximum size of about The size at birth or maturity is unknown for any other Glyphis species. A typical requiem shark in its external appearance, it is stocky, with two spineless dorsal fins and an anal fin. The first dorsal fin originates over the last third of the pectoral fins, with a free rear tip that is well in front of the pelvic fins. The second dorsal fin is relatively large, but much smaller than the first (about half the height). The anal fin is slightly smaller than the second dorsal fin and the pectoral fins are broad. A longitudinal upper precaudal pit is seen, but no interdorsal ridge. It is uniformly grey to brownish in color, with no discernible markings.

G. gangeticus can be identified by the first few lower front teeth, which have cutting edges along entire cusp, giving the cusps a claw like shape, and low cusplets. Also, a second dorsal fin that is about half the height of first dorsal is distinct to this species.

The Ganges shark, as its name suggests, is largely restricted to the rivers of eastern and northeastern India, particularly the Hooghly River of West Bengal, and the Ganges, Brahmaputra, and Mahanadi in Bihar, Assam, and Odisha, respectively. It is typically found in the middle to lower reaches of a river. One found in 2018 in a Mumbai fish market may have come from somewhere along the banks of the Arabian Sea. In theory, G. gangeticus could occur in shallow marine estuaries; however, no marine records of the species have been verified to date. Originally, the species was assigned a wide range in the Indo West Pacific, but this was found to be mostly based on other species of requiem sharks, particularly members of the genus Carcharhinus.

G. gangeticus is known to inhabit only freshwater, inshore marine, and estuarine systems in the lower reaches of the Ganges Hooghly River system. Their feeding habits are mostly unknown. The shark's small eyes and slender teeth suggest that it is primarily a fish eater and is adapted to turbid water.

It is probably viviparous, with a yolk sac placenta (speculation through analogy to related species of carcharhinids). The litter size and gestation period are unknown. However, this is not thought to be for breeding, as the case in anadromous and catadromous species. The presence of newborn individuals in the Hooghly River suggests that the young may be born in fresh water.

G. gangeticus was originally known only from three 19th century museum specimens, one each in the National Museum of Natural History in Paris, Natural History Museum, Berlin in Berlin, and the Zoological Survey of India in Calcutta. No records exist between 1867 and 1996, and the 1996 records have not been confirmed as G. gangeticus. A specimen collected upstream of the mouth of the Hooghly River at Mahishadal in 2001 was identified as G. gangeticus, but on photographs of the jaw only.

G. gangeticus is one of 20 sharks on the International Union for Conservation of Nature and Natural Resources Red List of endangered shark species. The species is currently classified as critically endangered. According to the organisation, fewer than 250 Ganges sharks are believed to exist. The need is urgent for a detailed survey of the shark fisheries of the Bay of Bengal. It is also believed to be part of the Asian shark fin trade.

In 2001, the Indian government banned the landing of all species of chondrichthyan fish in its ports. However, shortly afterwards, this ban was amended to cover only 10 species of chondrichthyans. These, including G. gangeticus, are protected under Schedule I, Part II A of the Wildlife Protection Act of India. Doubt exists about the effectiveness of this measure, however, because of difficulties in enforcement. A widespread, albeit widely dispersed, artisanal fishery exists for both local consumption and international trade. Compagno (1997) recommends an in depth survey of fishing camps and landing sites, along with a sampling program in the Ganges system to determine the current status of this shark along with other Gangetic elasmobranchs such as stingrays and sawfish. but most of the attacks attributed to it are probably the result of confusion with the bull shark Carcharhinus leucas. The biological differences between the Ganges shark and bull shark also point to a lower likelihood of attacks on humans by the Ganges shark. G. gangeticus has much narrower, higher, upper teeth and slender cusped, less heavily built lower teeth than C. leucas. Such small sharp teeth are more suitable for fish impaling, and less useful for dismembering tough mammalian prey than the stout teeth of the bull shark.