Separate Species of South Asian River Dolphins

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Recently, the detailed analysis of South Asian river dolphins has revealed that the Indus and Ganges River dolphins are not one, but two separate species.

About the Study

• The landmark study was carried out for 20 years and has been published in the Marine Mammal Science.
• The international team studied body growth, skull morphology, tooth counts, colouration and genetic makeup.
• Challenges in the Study
  • Researchers did not have access to fresh tissue samples so they used DNA out of skulls and skeletons, which were 20 to 30 to even 150 years old.
  • Both species occur in neighboring countries separated by an unfriendly international border so sharing of samples or data was a challenge.
  • Due to the protection status of Ganges Dolphin, one cannot transfer any tissue or sample to foreign countries without getting the Convention on International Trade in Endangered Species (CITES) permission from the Competent Authority of Government of India.
  • Finding dead animals was uncommon because they either float downstream or sink, and museum collections worldwide contain only a few specimens and most of them are damaged.
• Findings
  • It estimates that Indus and Ganges river dolphins may have diverged around 550,000 years ago.
  • The dolphins in the Indus river basin and those in the Ganges-Brahmaputra river basins are sufficiently distinct to be classified as species in their own right and the older status needs revision.

                                                                                              (Image Courtesy: WOL)

South Asian River Dolphins

• Presently, both are classified as two subspecies under Platanista gangetica.
  • The two subspecies Indus and Ganges river dolphins (P. g. minor and P. g. gangetica) belong to the family Platanistidae.
• These are often referred to as blind dolphins because they live in naturally muddy rivers and, over millions of years of evolution, have lost their eyesight and instead rely on a sophisticated sonar or echolocation system to navigate and catch prey.
• The population of Ganges river dolphins is declining and estimated at several thousand individuals spread across rivers systems in Bangladesh, India and Nepal.
• Meanwhile, Indus river dolphins, which occur primarily in Pakistan, have achieved an impressive recovery over the last 20 years, with an 80 per cent decline in the extent of their range.

Concerns

• Physical barriers such as dams and barrages created across the river reduced the gene flow to a great extent making the species vulnerable.
• River flow is also declining very fast as river water is being diverted through the barrages and this has affected the dolphin habitats.
• Previously, fishermen used to hunt dolphins and use their oil as bait. Now the practice of direct killing has stopped but they end up being accidental catches.
• Mechanised boats and fishing nets also cause accidental injury to the dolphins.
• Both point and nonpoint sources of pollution affect the dolphin habitat.

• Conservation
  • Both are classified as ‘Endangered’ species under the International Union for Conservation of Nature (IUCN) Red List.
  • Dolphins have been included in Schedule I of the Indian WildLife (Protection) Act 1972, in Appendix I of the CITES, in Appendix II of the Convention on Migratory Species (CMS).
• Suggestions
  • Though the Indian government has given legal protection to the dolphin, more ground action and close work with local communities are needed to help them survive.
  • The freshwater systems they inhabit must be managed with biodiversity as a top priority.

                                                                                                (Image Courtesy: WWF)

Source: TH