| Indus river dolphin | |
|---|---|
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| Size compared to an average human | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Platanistidae |
| Genus: | Platanista |
| Species: | P. minor |
| Binomial name | |
| Platanista minor Owen, 1853 | |
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| Ranges of theIndus river dolphin andGanges river dolphin | |
TheIndus river dolphin (Platanista minor) is a species offreshwater dolphin in the familyPlatanistidae. It isendemic to the rivers of theIndus basin inPakistan and northwesternIndia.[1] This dolphin was the first discovered side-swimming cetacean. In Pakistan, it occurs in theIndus river, patchily distributed in five small sub-populations that are separated by irrigation barrages. In India, a very small isolated population at a very high risk of extinction lives in theBeas river.
From the 1970s until 1998, theGanges 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 theSouth Asian river dolphin. However, more recent studies support them being distinct species. It is listed as the national mammal of Pakistan and the state aquatic animal ofPunjab, India.
The Indus river dolphin was described in 1853 byRichard Owen under the namePlatanista gangetica, var. minor, based on a dolphin skull, which was smaller than skulls of the Ganges river dolphin.[2]
The Indus and Ganges river dolphins were initially classified as a single species,Platanista gangetica. In the 1970s, they were considered to be distinct species, but again grouped as a single species in the 1990s. However, more recent studies of genes, divergence time, and skull structure support both being distinct species.[3]
The Ganges river dolphin split from the Indus river dolphin during thePleistocene, around 550,000 years ago.[4]
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 eyelens, rendering it effectivelyblind, although it may still be able to detect the intensity and direction of light. Navigation and hunting are carried out usingecholocation.The body is a brownish color and stocky at the middle. The species has a small triangular lump in place of adorsal fin. The flippers and tail are thin and large in relation to the body size, which is about 2–2.2 m (6 ft 7 in – 7 ft 3 in) in males and 2.4–2.6 m (7 ft 10 in – 8 ft 6 in) in females. The oldest recorded animal was a 28-year-old male 199 cm (78 in) in length.[5] Mature adult females are larger than males.Sexual dimorphism is expressed after females reach about 150 cm (59 in); the femalerostrum continues to grow after the male rostrum stops growing, eventually reaching approximately 20 cm (7.9 in) longer.[citation needed]
The Indus river dolphin occurs in the Indus River system.[1][6] Its range once stretched over about 3,400 km (2,100 mi) of the Indus River and its tributaries, but today, it only occurs in about 690 km (430 mi) of the river, and its range has declined by 80% since 1870; it is not present anymore in the tributaries.[6]A remnant population is present in theBeas River andHarike Wetland located inPunjab, India.[7]
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 theSutlej andYamuna changed their channels in ancient times while retaining their dolphin populations.[8]
It is thought that the Indus river dolphin swims on its side to efficiently navigate shallow waters during the dry season.[9]
The Indus river dolphin has been very adversely affected by human use of the river systems in the subcontinent. Entanglement infishing nets can cause significant damage to local population numbers. Some dolphins are still caught each year for their oil and meat that is used as a liniment, as anaphrodisiac and as bait forcatfish. Irrigation has also lowered water levels throughout their ranges.Water pollution 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 narrowedgene pool in which dolphins can breed. There are currently three sub-populations of Indus dolphins considered capable of long-term survival if protected.[6]The Beas River population is also threatened by extensive fishing that reduces prey availability, and accidental entangling in fishing nets causes fatalities.[10]
The Indus river dolphin is protected under Appendix I of theConvention on the International Trade of Endangered Species which prohibits the commercial international trade of the species (including parts and derivatives).[6]It is listed asEndangered on theIUCN Red List,[1] and by the U.S. governmentNational Marine Fisheries Service under the U.S.Endangered Species Act. 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).[11] 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 it no longer occurs.[12] According to an estimate conducted by the Wildlife Institute of India, only three individuals remain in theBeas River.[13]A satellite tagging effort was initiated in 2022.[14]
