Although they now live in separate Asian river systems, the Ganges and Indus River dolphins look identical because they share a common ancestor.
They are currently categorised as subspecies and scientists are considering the evidence that they have evolved into two species. Sadly, both are endangered; there are only one to two thousand Indus River dolphins and less than five thousand Ganges River dolphins left in the world.
Other names: Ganges River dolphin or Susu; Indus River dolphin or Bhulan or Shushuk
IUCN conservation status: Endangered
What do South Asian river dolphins look like?
This greyish-brown dolphin has an unusual looking head and face; their teeny eyes are only visible as pin-prick sized openings just above the end of their upturned mouth line. The very long, slender snout is lined with lots of sharp, pointy teeth which get longer towards the tip and are visible on the outside of the mouth. The dorsal fin is more of a low hump and the belly is rounded which gives these dolphins a stocky appearance. The triangular-shaped flippers are large and broad; they are squared-off at the end and have a crenulated trailing edge. The tail flukes are also large and wide.
What’s life like for a South Asian river dolphin?
South Asian River dolphins are not demonstrative or acrobatic; they usually surface quickly and unobtrusively although they do sometimes stick their snout right out of the water. They are generally found alone or in pairs, and occasionally in small groups. They tend to gather in places along the river where the best fishing spots are; in counter-current pools created near channel convergences, mid-channel islands, sharp meanders and man-made structures such as bridge pilings. These features help to concentrate nutrients and fish in the river.
South Asian river dolphins are blind; their eyes are tiny and lack lenses. Their vision is likely to have degenerated as a result of poor visibility in murky, sediment-laden river water. Unlike most dolphins, they have very flexible necks as their neck vertebrae are not fused. They are able to turn their heads sweeping back and forth in a scanning motion, while using echolocation to navigate and search for prey. They can swim upside down and on their sides, using one flipper to help feel for prey in the muddy river bed.
South Asian river dolphins are thought to reach sexual maturity at between 6 and10 years old. Each pregnancy lasts about a year and the calves stay with their mothers for a year before they are weaned. Lifespan is estimated at up to 30 years.
What do South Asian river dolphins eat?
South Asian river dolphins eat a variety of fresh water fish and invertebrates. Their long, thin snouts are designed for quick snapping actions to capture fast prey.
Where do South Asian river dolphins live?
Ganges River dolphins live in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems spanning three countries; Nepal, India and Bangladesh. They can be found in rivers flowing all the way from the foothills of the Himalayas downstream to the Bay of Bengal. The Indus River dolphin lives only in the Indus River, Pakistan.
During high water seasons created by monsoon rains, South Asian river dolphins are able to spread out and live in seasonal tributaries and lakes as well as the main river channels.
What's in a name?
South Asian river dolphins have many local names throughout the countries where they live. Most are related to the sound people hear when the dolphins surface to breathe. These include bhulan (Urdu and Sindhi); Sus and Swongsu (Nepali); Susu, Soonse and Sunsar (Hindi); Hiho and Shihu (Assamese); and Shusshuk, Foomach and Sishumaach (Bengali).
An endangered species
South Asian river dolphins are rated by IUCN as Endangered due not only to the huge reduction in their overall numbers, but also the ongoing shrinking of their habitats and freshwater places they are able to live.
The range of the South Asian river dolphin is predicted to continue to diminish as those living in sections of rivers isolated from others by dams and barrages disappear due to further habitat loss and climate change.
The Indus River dolphin is now limited to a 700 km stretch of the Indus mainstream which is about one-fifth of their historical range. More tragically, the last surviving dolphins are separated into three subpopulations and isolated from each other by barrages and this isolation makes them more vulnerable to other threats.
The Ganges River dolphin lives in one of the world’s most densely populated areas. Their overall range has shrunk and the remaining dolphins are divided into four subpopulations, isolated from one another by barrages.
South Asian river dolphins share their river habitats with crocodiles (gharials), freshwater turtles and wetland birds.
South Asian river dolphins are legally protected from hunting in all four countries they live in.
Compared to other river dolphins, South Asian river dolphins have smaller brains but the part of the brain used for acoustic functions is well developed.
Although they cannot see images as their eyes lack lenses to focus, they do have an optic nerve and retina and so can detect light and dark.
The ear opening is above the eye which is unlike that of other dolphins whose ear openings are just behind the eye.
Unfortunately these dolphins sometimes become stranded and trapped in irrigation canals as water levels fall in the dry season and their only hope is human rescue.
South Asian river dolphins need your help
The main threats...
- Dams and Barrages - the biggest threat South Asian river dolphins face is the existence of dams and barrages altering rivers for human needs. These structures are insurmountable physical barriers to the dolphins and prevent their free movement and seasonal migration in rivers. They have reduced the complexity of natural river flow and ecosystems and reduced habitats available for the dolphins. The surviving dolphins are now divided into isolated and vulnerable subpopulations. Dolphins trapped upriver of some dams have already disappeared. More dams and barrages are under construction or planned, driven by higher demands for fresh water supplies for agriculture, industry and urban areas and so South Asian river dolphin populations will continue to decline.
- Fishing nets - South Asian river dolphins get caught accidentally and die in gillnets. Both fishermen and dolphins fish in the same parts of the river where nutrients are richest and the fish are concentrated.
- Pollution- levels of pollution in rivers of South Asia are increasing and can be expected to carry on increasing as development is ongoing and there are few controls on pollutant discharges. Rivers are less able to dilute pollutants because water is increasingly removed to supply agricultural and industry demands.
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