River dolphins are a group of fully aquatic mammals that reside exclusively in freshwater or brackish water.
Important characteristics of river dolphins
1 . River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents.
2 . They range in size from the 5-foot long South Asian river dolphin to the 8-foot Amazon river dolphin.
3 . River dolphins use their conical-shaped teeth and long beaks to capture fast-moving prey in murky water.
4 . They have well-developed hearing that is adapted for both air and water.
5 . Dolphins send out high frequency clicks from an organ known as a melon. This allows river dolphins to produce biosonar for orientation. They are so dependent on echolocation that they can survive even if they are blind.Beyond locating an object, echolocation also provides the animal with an idea on the object’s shape and size.
6 . They do not really rely on vision since the water they swim in is usually very muddy.
7 . These species are well-adapted to living in warm, shallow waters, and, unlike other cetaceans, have little to no blubber.
8 . River dolphins are not very widely distributed; they are all restricted to certain rivers or deltas. This makes them extremely vulnerable to habitat destruction.
9 . River dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.
River Dolphins in the world
There are seven important species of river dolphins in the world –
1 . Amazon River Dolphin(Boto)-They are the pink river dolphin and are Vulnerable. They are found only in freshwater
2 . Tucuxi –They are found in Amazon and its tributaries, can live in both salt and freshwater.
3 . Yangtze river dolphin (Baiji) – They are found in China but has been declared “functionally extinct” in 2006.
4 . Yangtze/Finless Porpoise – They are Endangered and are found in the Yangtze River and its adjacent lake systems.
River Dolphins found in India
5 . Indus Dolphin (Bhulan) – They are endangered and functionally blind species of dolphins . Except for a small population of about 30 in India’s Beas River (185 km stretch between Talwara and Harike), Indus river dolphins live exclusively in the Indus river in Pakistan.Recently the Punjab government along with WWF-India has conduvted the first organised census on population of Indus Dolphin.
6 . Ganges River Dolphin (Susu) – It is endangered, can only live in freshwater and is essentially blind.
It has been declared as national aquatic animal.
7 . Irrawaddy Dolphin – They are Crtitically Endangered and live in both salt- and freshwater in South and Southeast Asia. Three exclusively freshwater populations are found in Irrawaddy River (Myanmar), Mekong River (Lao PDR, Cambodia) and Mahakam River (Indonesia). In addition, very small numbers survive in the partially freshwater Songkhla Lake (Thailand) and the brackish Chilika Lake (India). Irrawaddy dolphin is the only salt water dolphin found in India.