It inhabits the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Nepal, India, and Bangladesh. This vast area has been altered by the construction of more than 50 dams and other irrigation-related projects, with dire consequences for the river dolphins.
The Ganges River dolphin lives in one of the world's most densely populated areas, and is threatened by removal of river water and siltation arising from deforestation, pollution and entanglement in fisheries nets. In addition, alterations to the river due to barrages are also separating populations. Total population of the Ganga river dolphin is estimated to be between 2,500-3,000 in its entire distribution range, out of which more than 80% is within the Indian territory.
This dolphin is among the four "obligate" freshwater dolphins - the other three are the baiji now likely extinct from the Yangtze river in China, the bhulan of the Indus in Pakistan and the boto of the Amazon River in Latin America. Although there are several species of marine dolphins whose ranges include some freshwater habitats, these four species live only in rivers and lakes.
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'.
Dolphin is an indicator species. The presence of dolphin in a river system signals a healthy ecosystem. Since the river dolphin is at the apex of the aquatic food chain, its presence in adequate numbers symbolizes greater biodiversity in the river system and helps keep the ecosystem in balance.
Main threats to the Ganges River dolphin
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.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 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. 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.
Efforts have been made in India to test shark liver and sardine oil and fish offal to find an alternative for dolphin products. The latter appears promising.
Ganga river dolphins are listed in Schedule-1 of the wild life protection act thereby according them the highest degree of protection during hunting.
To mitigate the identified threats, WWF encourages local communities along a 164km-stretch of important dolphin habitat in the upper Ganges River to use natural fertilizers; not to dispose of domestic sewerage in the river; to improve sewerage management; to reforest the river bank; and to ban commercial fishing and sand-mining activities. WWF also monitors dolphin populations and threats in important dolphin habitats in other areas of the country.
Dolphin conservation has not figured in earlier attempts to clean the river — the Ganga Action Plan phase-I and phase-II were more focused on sewage treatment — though it was being run as a separate programme. The dolphin was also named the ‘National Aquatic Animal’ of India in 2009.
Nearly 50 per cent of the total population of dolphins in Ganga is now in Bihar.
Uttarakhand, Uttar Pradesh, Bihar, and West Bengal — have Dolphins Jharkhand, the other state through which the Ganga flows, does not have dolphins. Dolphin conservation was entirely dependent on the progress of the Ganga cleaning exercise. Dolphins breed in deep waters and feed in shallow waters. In the Ganga, excessive siltation has reduced the depth. A number of barrages and hydropower projects has interrupted the flow of water. In addition, the destruction of floodplains has affected the population of small fish which form the main diet of dolphins.
Irrawady river dolphins
They can survive both in fresh water and marine water. A small number of these are found in Myanmar, Indonesia and the Mekong river delta of south-east Asia. A few of them are in Bangladesh and in Orissa’s Chilka lake.
Dolphins do not breed in large numbers. On an average, a dolphin gives birth to five or six offspring during its life span, which is about 25 to 28 years.