Ganges river dolphin

The Ganges river dolphin split from the Indus river dolphin during the Pleistocene, around 550,000 years ago.[1] The earliest fossil identified as belonging to the species is only 12,000 years old.[10]

The Ganges river dolphin was formally classified as Delphinus gangeticus two separate times in 1801, by Heinrich Julius Lebeck[11] and William Roxburgh. They both likely used the type specimen, caught near Calcutta in late 1797 and sent to the Hunterian Museum in London. It may have been destroyed during World War II, but castings were previously made of the rostrum and parts of the lower jaw, which survive at the Natural History Museum.[12] Whether Lebeck or Roxburgh should be given credit has been debated over the centuries, but research by Kinze (2000) found that Lebeck's description was published on the 24 August while Roxburgh's was likely published no earlier than September, thus giving Lebeck the priority.[12][13] Elisha Gray coined the species name Platanista gangetica in 1835.[12]

This species and the Indus river dolphin, were initially classified as a single species, Platanista gangetica, but in the 1970s both were split into distinct species. However, in the 1990s, both species were again grouped as a single species. However, more recent studies of genes, divergence time, and skull structure support both being distinct species.[14][12]

Etymology

The species has multiple common names throughout its range. It is known as susu as a popular name; soons, soans, or soos in Hindi; shushuk in Bengali; hiho or hihu in Assamese; bhagirath (as a reference to the character of the same name from Hindu mythology); and shus or suongsu in Nepali. Its Sanskrit name in medieval times was likely shishumar, and during the Mughal era, it was known as pani suar.[12]

In Sundarbans, Bangladesh

It lives along the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India, and the Sapta Koshi and Karnali Rivers in Nepal.[15][16] The Ganges river dolphin favours deep pools, eddy countercurrents located downstream of the convergence of rivers and of sharp meanders, and upstream and downstream of midchannel islands.[16][17]

The Ganges river dolphin has a rectangular, ridgelike dorsal fin and females tend to be larger than males.[18] Ganges river dolphins usually are tan, chocolate brown, dark grey or light blue. They have an elongated, slender snout with sharp and very pointed teeth, similar to most river dolphins. The river dolphin has a rounded belly which, combined with their rectangular dorsal fin, makes them look particularly stocky in build compared to other dolphins. Their flippers and tail flukes are large and broad.[19] They have a large melon head used for echolocation, because they cannot see well. Their eyes are usually small due to the cloudy water.[18] Ganges river dolphins are usually 2.2-2.6 meters long (7–8 ft). The oldest recorded animal was a 28-year-old male, 199 cm in length, although they are estimated to live up to 30 years old.[19][20]

The Ganges river dolphins usually swim alone or in pairs and are not known to do acrobatic maneuvers near boats.[18] Little is known about their behavior because they are usually shy around boats and are hard to observe.[18] They are known to breach; however this is rare.[18]

The dolphin does not have a specific mating season. When a calf is born, 8–12 months after conception, it will stay with its mother for one year.[25]

Ganges river dolphins use echolocation to find food. They eat crustaceans such as prawns and fish including carp, mahseer, and even sharks such as the Ganges shark (Glyphis gangeticus). They may also take birds and turtles.[25]

Gangetic dolphin, 1894 book illustration

Ganga on a makara by Kalighat (1875)

The Ganges River dolphin has been listed as endangered under the IUCN Red List since 1996. Human activity has played a large role in the reduction of both their native range and population size. The Ganges river dolphin and other freshwater dolphin species have faced declines in population from stressors such as noise pollution, ship traffic, and fishery bycatch. Anthropogenic activity like dam construction and hydroelectric power plants also contribute to their endangered status.[26] They are also endangered due to pollution and overfishing for oil.[4][2] Entanglement in fishing nets as bycatch can cause significant damage to local populations, and individuals are taken each year by hunters; their oil and meat are used as a liniment, as an aphrodisiac, and as bait for catfish. Poisoning of the water supply from industrial and agricultural chemicals may also have been a contributing factor towards population decline, as these chemicals are biomagnified in the bodies of the dolphins.[27] An immediate danger for the species in National Chambal Sanctuary is the decrease in river depth and appearance of sand bars dividing the river course into smaller segments, as irrigation has lowered water levels throughout their range.[28]

A 2017 population assessment estimated that less than 3,500 individuals of Platanista gangetica exist throughout the species' range. The underlying surveys are temporally patchy and believed to contain uncertainty.

The Ministry of Environment and Forest declared the Gangetic dolphin the national aquatic animal of India. A stretch of the Ganges River between Sultanganj and Kahlgaon in Bihar has been declared a dolphin sanctuary and named Vikramshila Gangetic Dolphin Sanctuary, the first such protected area.

The Uttar Pradesh government in India is propagating ancient Hindu texts in hopes of raising the community support to save the dolphins from disappearing. One of the lines being versed from Valimiki's Ramayana, highlighted the force by which the Ganges emerged from Shiva's locks and along with this force came many species such as animals, fish, and the Shishumaar—the dolphin.[30]

On 31 December 2020, a dead adult dolphin was found at the Sharda canal in the Pratapgarh district in India. A video circulated on social media showing a dozen men beating the dolphin with sticks and an axe. On 7 January 2021, three people were arrested.[31] Similarly, there is another news in which a few fishermen caught one Gangetic dolphin and feasted upon it leading to arrest by Kaushambhi police in Uttar Pradesh.[32]

The species is protected from international trade by its listing in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. This makes commercial international trade prohibited.[3]

Bangladesh has established six sanctuaries in the Sundarbans.[33]

• Media related to Platanista gangetica at Wikimedia Commons