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Ganges and Indus River Dolphin (Platanista gangetica) - Wiki
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Ganges and Indus River Dolphin
From Wikipedia, the free encyclopedia
[Photo] Ganges River Dolphin (Platanista gangetica gangetica). Photographer:Brian D. Smith. Source: http://www.iucn.org/themes/ssc/actionplans/cetaceans/images.htm
The Ganges River Dolphin (Platanista gangetica gangetica) and Indus River Dolphin (Platanista gangetica minor) are two sub-species of freshwater or river dolphins found in Bangladesh, India, Nepal and Pakistan. The Ganges River Dolphin is primarily found in the Ganges and Brahmaputra Rivers and their tributaries in India, Bangladesh and Nepal while the Indus River Dolphin is only found in the Indus river in Pakistan. From the 1970s until 1998 they were regarded as separate species, however in 1998 their classification was changed from two separate species to subspecies of a single species (see taxonomy below).
Other names
Both subspecies: South Asian River Dolphin, Blind River Dolphin, Side-swimming Dolphin
Ganges subspecies: Gangetic Dolphin, Ganges Susu, Shushuk
Indus subspecies: Bhulan, Indus Dolphin, Indus blind dolphin
Taxonomy
The species was described by two separate authors Lebeck and Roxburgh in the year 1801 and it is unclear to whom the original description should be ascribed. Until the 1970s the Indus and Ganges River Dolphins were regarded as a single species. The two populations are geographically separate and have not interbred for many hundreds if not thousands of years. Based on differences in skull structure, vertebrae and lipid composition scientists declared the two populations as separate species in the early 1970's. In 1998 the results of these studies were questioned and the classification reverted to the pre-1970 consensus of a single species containing two subspecies until the taxonomy could be resolved using modern techniques such as molecular sequencing. Thus, at present, there are two subpecies recognized in the genus Platanista, Platanista gangetica minor (the Indus dolphin) and Platanista gangetica gangetica (the Ganges River dolphin).
Physical description
The Ganges and Indus River Dolphins are essentially identical in appearance. They have the long, pointed snout 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 echo-location. The body is a brownish colour and stocky at the middle. The species has only a small triangular lump in the place of a dorsal fin. The flippers and tail are thin and large in relation to the body size, which is about 2-2.2 metres in males and 2.4-2.6 m in females. The oldest recorded animal was a 28 year old male 199 centimetres in length. Mature adult females are larger than males. Sexual dimorphism 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.
The species feeds on a variety of shrimp and fish, including carp and catfish. Dolphins are usually encountered on their own or in loose aggregations, they do not form tight obviously interacting groups.
Population and distribution
The Ganges subspecies can be found in the Ganges River as well as the Brahmaputra, Meghna, Karnaphuli and Sangu river systems of India, Bangladesh, Nepal and Bhutan. Relatively high population densities have been observed near the Vikramshila Gangetic Dolphin Sanctuary in India and in the Sangu River in southern Bangladesh. Very few individuals (perhaps 20) are present in Nepal in the Karnali River. The total population is unknown, but certainly numbers in the hundreds and there are perhaps as many as a few thousand (but see "Human interaction" below).
The River Chambal originating in western India joins the Ganges River near Allahabad. Singh and Sharma (1985) estimated the presence of at least 45 dolphins between Batesura and Pachhnada (total 320 km) in the River Chambal during 1983-1985 (Fig.1). This is an observed density of one adult per about 6.5 km.
The Indus subspecies resides in the Indus River in Pakistan. In the nineteenth century dolphins were found in the Indus River from the estuary into the foothills of the Himalayas and in the Sutlej, Ravi, Chenab and Jhelum tributaries of the Indus. Today dolphins are present in only 1000 km of the Indus River in five subpopulations separated from one another by irrigation barrages. Approximately 99% of the dolphin population occurs in 690 km of river length which represents a range decline of 80% since distribution was mapped in the 1870s.
A comprehensive population census of the Indus Dolphin that was completed in 2001 by WWF-Pakistan concluded that there are approximately 1,100 individuals alive today. A pronounced increase in dolphin abundance and encounter rate was observed in each subsequent downstream subpopulation (except the last). The three largest subpopulations were between Chashma and Taunsa Barrages (84 dolphins; 0.28/km), Taunsa and Guddu Barrages (259 dolphins; 0.74/km) and Guddu and Sukkur Barrages (602 dolphins; 3.60/km).
Human interaction
Both subspecies have been very adversely affected by human use of the river systems in the sub-continent. Entanglement in fishing nets 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 and as bait for catfish. Irrigation has lowered water levels throughout both subspecies' 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 more than 50 dams along many rivers, causing the segregation of populations and a narrowed gene pool in which dolphins can breed. There are currently three sub-populations of Indus Dolphins considered capable of long-term survival if protected.
Both subspecies are listed by the IUCN as endangered on their Red List of Threatened Species.
The immediate danger for the resident population of P. gangeticus in National Chambal Sanctuary is the decrease in river depth and appearance of sand bars dividing the river course into smaller segments.
http://en.wikipedia.org/wiki/Ganges_and_Indus_River_Dolphin
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Scientific Name: Platanista gangetica (Roxburgh, 1801)
Common Names:
English – Ganges River Dolphin, Indus River Dolphin, Blind River Dolphin, Ganges Susu, Ganges Dolphin, South Asian River Dolphin
French – Plataniste Du Gange, Sousou
Spanish – Delfín Del Ganges
Synonyms:
Platanista gangetica (Roxburgh, 1801)
Platanista minor Owen, 1853 |
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