Context: In a recent research, detailed analysis of South Asian river dolphins has revealed that the Indus and Ganges River dolphins are not one, but two separate species.

• Currently, they are classified as two subspecies under Platanista gangetica and this needs a revision.

Key Findings

• The study estimates that Indus and Ganges river dolphins may have diverged around 550,000 years ago.
• The ancient DNA were studied out of skulls and skeletons, which were 20 to 30 to even 150 years old.
• Studying the sequences in the DNA made it clear that the Ganges dolphins and the Indus dolphins were quite different.

Conservation status of dolphins

• The Indus and Ganges River dolphins are both classified as ‘Endangered’ species by the International Union for Conservation of Nature (IUCN).
• The physical barriers such as dams and barrages created across the river has reduced the gene flow to a great extent making the species vulnerable.
• The river flow is also declining very fast as river water is being diverted through the barrages and this has affected the dolphin habitats.
• Mechanised boats are also causing accidental injury to the dolphins.

Key Points

• River dolphins are aquatic mammals that reside exclusively in freshwater or brackish water.
• The Ganges River dolphins live in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems spanning three countries; Nepal, India and Bangladesh.
  They can only live in freshwater and is essentially blind. 
• There are only five extant species of river dolphins left and all of them are endangered or critically endangered. They are found in regions of Asia and South America.
• The Ganges River Dolphin is a type of South Asian river dolphin and is found in the Ganga and Brahmaputra rivers and their tributaries.
• It is classified as ‘endangered’ in the IUCN Red List.
• It has been declared the ‘national aquatic animal of India’.
• It is also the official animal of the city of Guwahati.
• South Asian river dolphins have poor eyesight and rely on echolocation to catch prey.

Echolocation is a phenomenon in which animals emit calls out to the environment and listen to the echoes of those calls that return from various nearby objects. They use these echoes to locate and identify objects.

• Echolocation is also known as biosonar.
• Dolphins and sperm whales use echolocation to navigate dark oceans and catch prey.
• River dolphins are at risk because of pollution, dams, shipping and bycatch.
• Dolphins are important indicators for the health of the rivers they live in.

Irrawaddy Dolphins

• They are a species of oceanic dolphins found in discontinuous subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.
• The Sunderban delta is a unique ecological space where Gangetic as well as Irrawaddy Dolphin are present, spread over India as well as Bangladesh.
• The government had announced the initiation of a Project Dolphin along the lines of Project Tiger in order to enhance the number of river dolphins.