Irrawaddy river shark
Encyclopedia
The Irrawaddy river shark (Glyphis siamensis) is a species
of requiem shark
, family
Carcharhinidae, known only from a single museum specimen originally caught at the mouth of the Irrawaddy River in Myanmar
. A plain gray, thick-bodied shark with a short rounded snout, tiny eyes, and broad first dorsal fin
, the Irrawaddy river shark is difficult to distinguish from other members of its genus without anatomical examination. Virtually nothing is known of its natural history; it is thought to be a fish-eater with a viviparous mode of reproduction. The International Union for Conservation of Nature (IUCN) has assessed this species as Critically Endangered
, as its distribution is extremely limited and suffers heavy fishing pressure and habitat degradation.
ichthyologist Franz Steindachner
, in Annalen des Naturhistorischen Museums in Wien (volume 11, 1896). 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.
of the Irrawaddy River near Yangon
, Myanmar
, apparently inhabiting brackish water
in a large, heavily silt
-laden river lined with mangrove forests.
The first dorsal fin
is broad and triangular, originating over the rear pectoral fin bases with its free rear tip ending in front of the pelvic fin origins. The second dorsal fin is half as tall as the first, and there is no ridge between the dorsal fins. The trailing margin of the anal fin has a deep notch. The coloration is a plain grayish brown above and white below, without conspicuous fin markings. This shark most closely resembles the Ganges shark
(G. gangeticus), but has more vertebrae (209 versus 169) and fewer teeth (29/29 versus 32–37/31–34).
l connection, as in other requiem sharks.
ting but also line and electrofishing
, occurs in the stretch of river where the sole Irrawaddy river shark specimen was caught. Habitat degradation poses a further threat to this shark, including water pollution
and the clearing of mangrove trees for fuel, construction materials, and other products. This shark may be naturally rare, which along with its highly restricted range, probable overfishing
, and loss of habitat, has led the International Union for Conservation of Nature (IUCN) to list it as Critically Endangered
. Despite fishing and scientific surveys in the area, no more Irrawaddy river sharks have been recorded in the hundred-plus years since the first.
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 museum specimen originally caught at the mouth of the Irrawaddy River in Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
. A plain gray, thick-bodied shark with a short rounded snout, tiny eyes, and broad 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...
, the Irrawaddy river shark is difficult to distinguish from other members of its genus without anatomical examination. Virtually nothing is known of its natural history; it is thought to be a fish-eater with a viviparous mode of reproduction. The International Union for Conservation of Nature (IUCN) has assessed this species as Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
, as its distribution is extremely limited and suffers heavy fishing pressure and habitat degradation.
Taxonomy
The only known Irrawaddy river shark was collected in the 19th century and described as Carcharias siamensis by AustrianAustrians
Austrians are a nation and ethnic group, consisting of the population of the Republic of Austria and its historical predecessor states who share a common Austrian culture and Austrian descent....
ichthyologist Franz Steindachner
Franz Steindachner
Franz Steindachner was an Austrian zoologist.- Work and career :Being interested in natural history, Steindachner took up the study of fossil fishes on the recommendation of his friend Eduard Suess...
, in Annalen des Naturhistorischen Museums in Wien (volume 11, 1896). However, subsequent authors doubted the validity of this species, regarding it as an abnormal bull shark
Bull shark
The bull shark, Carcharhinus leucas, also known as Zambezi shark or unofficially known as Zambi in Africa and Nicaragua shark in Nicaragua, is a shark common worldwide in warm, shallow waters along coasts and in rivers...
(Carcharhinus leucas), until in 2005 shark systematist 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,...
recognized it as distinct member of the genus Glyphis.
Distribution and habitat
The Irrawaddy river shark is found in the deltaRiver delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
of the Irrawaddy River near Yangon
Yangon
Yangon is a former capital of Burma and the capital of Yangon Region . Although the military government has officially relocated the capital to Naypyidaw since March 2006, Yangon, with a population of over four million, continues to be the country's largest city and the most important commercial...
, Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
, apparently inhabiting brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
in a large, heavily silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
-laden river lined with mangrove forests.
Description
The sole Irrawaddy river shark specimen is a 60 cm (23.6 in) long immature male, suggesting an adult length of 1–3 m (3.3–9.8 ft). Like other river sharks, its body is robustly built with a high back that slopes down to a broadly rounded snout shorter than the mouth is wide. The eyes are minute, and the nares are small and widely spaced. The mouth contains 29 tooth rows in the upper and lower jaws, and has short furrows at the corners. The upper teeth are broad, triangular, and upright, with serrated margins, while the lower teeth at the front are more finely serrated with a pair of small cusplets at the base.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 broad and triangular, originating over the rear pectoral fin bases with its free rear tip ending in front of the pelvic fin origins. The second dorsal fin is half as tall as the first, and there is no ridge between the dorsal fins. The trailing margin of the anal fin has a deep notch. The coloration is a plain grayish brown above and white below, without conspicuous fin markings. This shark most closely resembles the Ganges shark
Ganges shark
The Ganges shark is a rare species of requiem shark found in the Ganges River of India. It should not be confused with the Bull shark, which also inhabits the Ganges River and is sometimes incorrectly referred to as the Ganges shark....
(G. gangeticus), but has more vertebrae (209 versus 169) and fewer teeth (29/29 versus 32–37/31–34).
Biology and ecology
The small teeth of the Irrawaddy river shark suggests that it mainly preys on fish, while its small eyes are consistent with the extremely turbid water in which it hunts. Reproduction is presumably viviparous, with the young sustained by a placentaPlacenta
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, as in other requiem sharks.
Human interactions
Intensive artisanal fishing, mainly gillnetGillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
ting but also line and electrofishing
Electrofishing
Electrofishing uses electricity to stun fish before they are caught. Electrofishing is a common scientific survey method used to sample fish populations to determine abundance, density, and species composition...
, occurs in the stretch of river where the sole Irrawaddy river shark specimen was caught. Habitat degradation poses a further threat to this shark, including water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
and the clearing of mangrove trees for fuel, construction materials, and other products. This shark may be naturally rare, which along with its highly restricted range, probable overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
, and loss of habitat, has led the International Union for Conservation of Nature (IUCN) to list it as Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
. Despite fishing and scientific surveys in the area, no more Irrawaddy river sharks have been recorded in the hundred-plus years since the first.