River dolphins

Plataniste or Ganges river dolphin (<i>Platanista gangética</i>), Karnaphuli river, ... rel=
Plataniste or Ganges river dolphin (Platanista gangética), Karnaphuli river, Bangladesh.
© WWF-Canon / François Xavier PELLETIER

Key Facts

  • Status

    IUCN: Vulnerable to Critically Endangered

  • Population

    Fewer than 100 to tens of thousands, depending on the species

  • Habitat

    Coastal, brackish, and fresh waters

Less famous than their marine cousins, river dolphins are rapidly disappearing - along with their natural river habitats

River dolphins and porpoises swim in some of the world's mightiest rivers, including the Ganges, Indus, Yangtze, Mekong, and Amazon. But these river basins are also home to over 15 per cent of our planet's people and include some of the most densely populated, and poorest, areas on Earth.

Dam-building, entanglement in fishing nets, boat traffic, and pollution have led to drastic declines in dolphin populations over the last several decades. Several Asian species are now amongst the most endangered of all cetaceans. Urgent action is needed to prevent these charismatic animals, about which we still know very little, from becoming extinct.

There are seven species of freshwater cetacean:

1. Also known as the pink river dolphin or boto, the Amazon river dolphin can only live in freshwater. It is found throughout much of the Amazon and Orinoco River Basins in Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela. It is the most abundant freshwater cetacean and probably numbers in the tens of thousands. However, it is classified as Vulnerable, with several dams having already fragmented the Amazonian population, and many more proposed.

2. The tucuxi lives in both salt- and freshwater and is found on the east coast of Central and South America. A riverine sub-species, S. f. fluviatilis, is found in the Amazon River and its main tributaries in northern Brazil, Peru, Colombia, and Ecuador, as well as in the lower Orinoco River in Venezuela. Classified as Data Deficient, its population is not known but it is not thought to be immediately threatened.

3. The Yangtze river dolphin, or baiji, was declared "functionally extinct" in 2006 after scientists failed to locate any remaining animals. Baiji once lived in the lower and middle reaches of the Yangtze River, Fuchun River, and in Dongting and Poyang Lakes, China.

4. The Endangered Ganges river dolphin, or susu, can only live in freshwater and is essentially blind. It once ranged throughout the Ganges-Brahmaputra- Meghna and Karnaphuli-Sangu river systems of Nepal, India, and Bangladesh, from the Himalayan foothills to the Bay of Bengal. Today its population is divided by dams into isolated groups and has a much reduced range. The lowest estimate for the total population is 1,200–1,800 individuals.

5. Closely related to the Ganges river dolphin, the Endangered Indus river dolphin, or bhulan, is found in Pakistan’s Indus River. One hundred years ago, the sub-species lived throughout the 3,500km-long river and its tributaries. Today around 1,100 individuals survive in a 1,375km-stretch of the Indus, divided into isolated populations by six barrages (a type of dam).

6. The Irrawaddy dolphin lives in both salt- and freshwater, and is found in a few locations in South and Southeast Asia. There are three exclusively freshwater populations: about 70–100 individuals live in a 190km-stretch of the Mekong River (Lao PDR, Cambodia); 33–50 live in a 420km-stretch of the Mahakam River (Indonesia); and about 59 live in a 370km-stretch of the Ayeyarwady River (Myanmar). In addition, very small numbers survive in the partially freshwater Songkhla Lake (Thailand) and the brackish Chilka Lake (India). The freshwater populations are all classified as Critically Endangered, as is the Songkhla Lake population.

7. The finless porpoise is the only porpoise species that can live in freshwater. It is found in coastal waters Southeast and East Asia, with a sub-species, N. p. asiaeorientalis, found in the Yangtze River and its adjacent lake systems. Classified as Endangered, a 2006 survey estimated the population of this freshwater sub-species at just 1,200-1,400.

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