The Ganges River Dolphin (Platanista gangetica gangetica) is a freshwater mammal adapted to life in murky river environments. It has an elongated snout, which can reach up to 20% of its body length, a low, ridgelike dorsal fin, and large, paddle-shaped pectoral flippers. The dolphin’s eyes are small and lack a lens, making it functionally blind and reliant on echolocation for navigation and hunting in its opaque habitat.
Geographic Range: The Major River Systems
The Ganges River Dolphin primarily inhabits the extensive freshwater river systems of the Indian subcontinent. Its distribution spans the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems. These interconnected river basins cover parts of India, Bangladesh, and Nepal, extending from the Himalayan foothills to the Ganges Delta.
In India, dolphins are found in the Ganges River and its tributaries, including the Yamuna, Chambal, and Kosi Rivers. Significant populations exist in the main Ganges stem, particularly in Bihar, and in the Brahmaputra River system. In Nepal, their numbers are much smaller, with fewer than 100 individuals recorded in tributaries like the Karnali and Koshi river systems.
Microhabitats: Preferred Riverine Environments
Within these vast river systems, Ganges River Dolphins exhibit preferences for specific microhabitats that offer optimal conditions for foraging and survival. They commonly inhabit deeper sections of the river, particularly favoring areas with eddy countercurrents. These locations are often found downstream of river confluences, around sharp river bends, or near mid-channel islands.
These environments offer calmer waters and higher concentrations of fish, their primary prey. During the monsoon season, rising water levels allow dolphins to disperse into seasonal tributaries and flooded lowlands. They also prefer areas with complex riverbed structures, where they sweep the bottom with their flexible necks and snouts to locate prey.
Historical vs. Present Distribution
Historically, the Ganges River Dolphin’s range was more expansive, but human activities and environmental changes have led to significant habitat contraction and fragmentation. The construction of dams and barrages is a primary factor restricting dolphin movement and access to historical areas. These structures create physical barriers, preventing free migration, especially during seasonal water level changes.
Consequently, the species is now extinct from many former distribution ranges, and remaining populations are often isolated. For example, dolphins have not been reported in sections of the Yamuna River above the Chambal River confluence since 1967. The Ganges River Dolphin’s geographic range has diminished, with current populations severely fragmented across India, Nepal, and Bangladesh.