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The Indus river dolphin (''Platanista minor''), also known as the ''bhulan'' in
Urdu Urdu (;"Urdu"
'' Sindhi, is a species of
toothed whale The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species o ...
in the family Platanistidae. It is
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to the Indus River Basin of
Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-la ...
and northwestern
India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...
. This dolphin was the first discovered side-swimming cetacean. It is patchily distributed in five small, sub-populations that are separated by irrigation barrages. From the 1970s until 1998, the Ganges River dolphin (''Platanista gangetica'') and the Indus dolphin were regarded as separate species; however, in 1998, their classification was changed from two separate species to subspecies of a single species. However, more recent studies support them being distinct species. It has been named as the national mammal of Pakistan, and the state aquatic animal of
Punjab, India Punjab (; ) is a state in northern India. Forming part of the larger Punjab region of the Indian subcontinent, the state is bordered by the Indian states of Himachal Pradesh to the north and northeast, Haryana to the south and southeast, an ...
.


Taxonomy

The Ganges river dolphin split from the Indus river dolphin during the
Pleistocene The Pleistocene ( , often referred to as the '' Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed i ...
, around 550,000 years ago. This species and the Indus river dolphin, were initially classified as a single species, ''Platanista gangetica'', but in the 1970s both were split into distinct species. However, in the 1990s, both species were again grouped as a single species. However, more recent studies of genes, divergence time, and skull structure support both being distinct species. Alternative names for the Indus River Dolphin include the Indus blind dolphin, side-swimming dolphin, and ''bhulan''.


Distribution

The Indus river dolphin presently only occurs in the Indus River system. These dolphins occupied about 3,400 km of the Indus River and the tributaries attached to it in the past. But today, its only found in one fifth of this previous range. Its effective range today has declined by 80% since 1870. It no longer exists throughout the tributaries, and its home range is only 690 km of the river. This dolphin prefers a freshwater habitat with a water depth greater than 1 meter and that have more than 700 meters squared of cross-sectional area. Today this species can only be found in the Indus River's main stem, along with a remnant population in the
Beas River The Beas River ( Sanskrit: ; Hyphasis in Ancient Greek) is a river in north India. The river rises in the Himalayas in central Himachal Pradesh, India, and flows for some to the Sutlej River in the Indian state of Punjab. Its total length i ...
. Since the two originally inhabited river systems – between the Sukkur and Guddu barrage in Pakistan's Sindh Province, and in the Punjab and Khyber Pakhtunkhwa Provinces – are not connected in any way, how they were colonized remains unknown. The river dolphins are unlikely to have travelled from one river to another through the sea route, since the two estuaries are very far apart. A possible explanation is that several north Indian rivers such as the
Sutlej The Sutlej or Satluj River () is the longest of the five rivers that flow through the historic crossroads region of Punjab in northern India and Pakistan. The Sutlej River is also known as ''Satadru''. It is the easternmost tributary of the I ...
and
Yamuna The Yamuna ( Hindustani: ), also spelt Jumna, is the second-largest tributary river of the Ganges by discharge and the longest tributary in India. Originating from the Yamunotri Glacier at a height of about on the southwestern slopes of ...
changed their channels in ancient times while retaining their dolphin populations.


Description

The Indus dolphin has the long, pointed nose characteristic of all river dolphins. The teeth are visible in both the upper and lower jaws even when the mouth is closed. The teeth of young animals are almost an inch long, thin and curved; however, as animals age the teeth undergo considerable changes and in mature adults become square, bony, flat disks. The snout thickens towards its end. The species does not have a crystalline eye lens, rendering it effectively blind, although it may still be able to detect the intensity and direction of light. Navigation and hunting are carried out using echolocation. The body is a brownish color and stocky at the middle. The species has a small triangular lump in place of a
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through co ...
. The flippers and tail are thin and large in relation to the body size, which is about 2-2.2 meters in males and 2.4–2.6 meters in females. The oldest recorded animal was a 28-year-old male 199 centimeters in length. Mature adult females are larger than males.
Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
is expressed after females reach about 150 cm; the female rostrum continues to grow after the male rostrum stops growing, eventually reaching approximately 20 cm longer. Calves have been observed between January and May and do not appear to stay with the mother for more than a few months. Gestation is thought to be approximately 9–10 months.


Diet

The species feeds on a variety of crustaceans and fish, including prawns, carp, catfish, gobies, etc.


Human interaction

The Indus river dolphin has been very adversely affected by human use of the river systems in the subcontinent. Entanglement in
fishing net A fishing net is a net used for fishing. Nets are devices made from fibers woven in a grid-like structure. Some fishing nets are also called fish traps, for example fyke nets. Fishing nets are usually meshes formed by knotting a relatively ...
s can cause significant damage to local population numbers. Some individuals are still taken each year and their oil and meat used as a liniment, as an
aphrodisiac An aphrodisiac is a substance that increases sexual desire, sexual attraction, sexual pleasure, or sexual behavior. Substances range from a variety of plants, spices, foods, and synthetic chemicals. Natural aphrodisiacs like cannabis or cocain ...
and as bait for
catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species aliv ...
. Irrigation has lowered water levels throughout their ranges. Poisoning of the water supply from industrial and agricultural chemicals may have also contributed to population decline. Perhaps the most significant issue is the building of dozens of dams along many rivers, causing the segregation of populations and a narrowed
gene pool The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. Description A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can su ...
in which dolphins can breed. There are currently three sub-populations of Indus dolphins considered capable of long-term survival if protected.


Conservation status

The Indus river dolphin is listed by the
IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natur ...
as endangered on their Red List of Threatened Species and by the U.S. government National Marine Fisheries Service under the U.S.
Endangered Species Act The Endangered Species Act of 1973 (ESA or "The Act"; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of ec ...
. It is the second most endangered cetacean in the world. As of 2017 it is estimated that there are only about 1,800 individuals remaining (up from 1,200 estimated in 2001). A demonstrable increase in the main river population of the Indus subspecies between 1974 and 2008 may have been driven by permanent immigration from upstream tributaries, where the species no longer occurs. There are many threats to their survival. Reckless and extensive fishing that reduces their prey availability is a large factor. Also, they are sometimes accidentally entangled in the fishing nets which can cause fatalities. Deforestation that occurs along the river basin is causing sedimentation which degrades the dolphin's habitat. Another factor in their decline is the construction of cross-river structures such as dams and barrages. These are a problem because they cause more isolation in the already small sub-populations. Lastly, human induced water pollution is a major threat factor. This pollution is usually in the form of either industrial and human waste, or agricultural run-off containing high amounts of chemical fertilizers and poisonous pesticides. Studies suggest that a better understanding of this species ecology is needed in order to develop good conservation plans. Regular monitoring is also a necessity to assess the population's status and factors causing its decline. There are currently several organizations that are helping to conserve the Indus dolphin. The
World Wildlife Fund The World Wide Fund for Nature Inc. (WWF) is an international non-governmental organization founded in 1961 that works in the field of wilderness preservation and the reduction of human impact on the environment. It was formerly named the Wor ...
(WWF) is involved in rescue missions and helping to reduce pollution in the river. A satellite tagging effort was begun in 2022. In addition
WWF Pakistan
is assisting in educating the public, and have arranged training courses for many institutions. The species is protected under Appendix I of the Convention on the International Trade of Endangered Species which prohibits the commercial international trade of the species (including parts and derivatives).


See also

*
South Asian river dolphin South Asian river dolphins are toothed whales in the genus ''Platanista'', which inhabit fresh water habitats in the northern Indian subcontinent. They were historically considered to be one species (''P. gangetica'') with the Ganges river d ...


References


Further reading

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External links

{{DEFAULTSORT:Indus River dolphin River dolphins Mammals of Pakistan Mammals of India National symbols of Pakistan EDGE species Mammals described in 1853 Taxa named by Richard Owen Taxobox binomials not recognized by IUCN