Context-The annual Ganges river dolphin census, undertaken by World Wide Fund for Nature-India in collaboration with the Uttar Pradesh Forest Department along about 250-km-long riverine stretch of Upper Ganga between Hastinapur Wildlife Sanctuary and Narora Ramsar site began in Bijnor on Wednesday

New Method

• Unlike previous years, when direct counting method was used, this year the tandem boat survey method is being used.
• Tandem boat survey method developed by the renowned river and marine ecologist Gill Braulik, provides a more accurate count of the endangered species. Here the officials use two inflated boats which move in tandem to count the dolphins. After collating the data, statistical tools are employed to arrive at the final count. In this process, we don’t announce the number of sightings on a daily basis.” Ms. Braulik, who is known for her work on Indus river dolphins, is also participating in the census.

Obligate freshwater dolphin

Yangtze river dolphin (Baiji)

• Listed as critically endangered in IUCN redlist and now likely extinct from the Yangtze river in China. It is a type of freshwater dolphin thought to be the first dolphin species driven to extinction due to the impact of humans.

Indus river dolphin (Bhulan)

• Listed as endangered in IUCN redlist.Now it swims in the lower parts of the Indus River in Pakistan. Another small, isolated population can be found in the Beas River in India.

Amazon river dolphin (Boto or pink river dolphin)

• Listed as vulnerable in IUCN redlist.It swims throughout much of the famed South American river basin and the neighboring Orinoco river basin that stretches through Colombia and Venezuela.

Ganges river dolphin (Susu)

• Listed as endangered in IUCN redlist.
• Locally known as susu, which refers to the noise the dolphin is said to make when it breathes, this swimmer is essentially blind and can detect only the direction of light.

About Ganges river dolphin (Susu)

Physical description

• A long thin snout, rounded belly, stocky body and large flippers are characteristics of the Ganges River dolphin. Although its eye lacks a lens (this species is also referred to as the "blind dolphin"), the dolphin still uses its eye to locate itself. The species has a slit similar to a blowhole on the top of the head, which acts as a nostril
• Being a mammal, the Ganges River dolphin cannot breathe in the water and must surface every 30-120 seconds. Because of the sound it produces when breathing, the animal is popularly referred to as the 'Susu'.

Breeding

• The gestation lasts from 9 to 11 months, and one calf is usually born, once every 2 to 3 years. There is no specific birth period, although females usually give birth from October to March, with a peak in December and January at the onset of the dry season.

Diet

• The diet includes a variety of fish and invertebrates, namely prawns, clams, catfish, freshwater sharks, mahseers (except in India), gobies and carp. Ganges River dolphins normally chase surface dweller fishes and grovel mud dweller fishes in shallow water with the help of their long snout. They cannot chew and usually swallow their prey.

Threats

Habitat and subspecies under severe threat

• The survival of the Ganges River dolphin is threatened by unintentional killing through entanglement in fishing gear; directed harvest for dolphin oil, which is used as a fish attractant and for medicinal purposes; water development projects (e.g. water extraction and the construction of barrages, high dams, and embankments); industrial waste and pesticides; municipal sewage discharge and noise from vessel traffic; and overexploitation of prey, mainly due to the widespread use of non-selective fishing gear.

Habitat loss and degradation

• More than 50 dams and irrigation-related projects have had an adverse impact on the habitat of this species. These projects result in major changes in the flow, sediment load, and water quality of rivers, which affects the quality of waters downstream.
• As a result, there has been a serious decrease in fish production, while the extraction of river water and siltation from deforestation are also degrading the species' habitat. In some cases, habitat alterations have resulted in the genetic isolation of dolphin populations.

Pollution

• Pollution levels are a problem, and are expected to increase with the development of intensive modern industrial practices in the region. Compounds such as organochlorine and butyltin found in the tissues of Ganges River dolphins are a cause for concern about their potential effects on the subspecies.

Fisheries bycatch

• Bycatch in gillnets and line hooks is also a major source of mortality for this subspecies.

Directed take

• Although the killing of this dolphin for meat and oil is thought to have declined, it still occurs in the middle Ganges near Patna, in the Kalni-Kushiyara River of Bangladesh, and in the upper reaches of the Brahmaputra. In fisheries for large catfish in India and Bangladesh, dolphin oil and body parts are used to lure prey, and Ganges River dolphins are used to this end.