Tuesday Mar 23, 2021
After two decades of research, scientists have recognised the endangered Indus and Ganges river dolphins as separate species – raising the number of river dolphin species worldwide to six.
Since the 1990s, river dolphins in South Asia were considered to constitute a single threatened species, but a study published today in Marine Mammal Science concludes that the dolphins in the Indus River and in the Ganges-Brahmaputra Rivers are sufficiently distinct to be classified as species in their own right.
The work, which took 20 years to complete, was led by Dr Gill Braulik of the Sea Mammal Research Unit at the University of St Andrews, who travelled across India and Pakistan to gather data for the study, including searching for dolphin skulls to measure. The research shows that the two river dolphin species have different numbers of teeth, colouration, growth patterns and skull shapes as well as clear genetic differences.
“Recognising the differences between Indus and Ganges river dolphins is extremely important, as only a few thousand individuals of each species remain,” said Dr Braulik. “They have long been regarded as two of the world’s most threatened mammals. My hope is that our findings will bring much-needed attention to these remarkable animals, which will help to prevent them from sliding towards extinction.”
The research involved a long-term collaboration between the University of St Andrews, WWF-Pakistan, Patna University in India, and the Southwest Fisheries Science Centre of the National Oceanic and Atmospheric Administration in the US as well as many other researchers in South Asia.
The Indus and Ganges river dolphins 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. Both species are threatened by accidental entanglement and drowning in fishing nets, by the construction of hydropower dams and irrigation barrages, and pollution of their waterways – and are listed as "endangered" on the International Union for Conservation of Nature (IUCN) Red List.
According to Dr Braulik, “The rapid decline and extinction of the Yangtze River dolphin this century was a very clear warning: we need to act quickly to protect the remaining species of river dolphins, including the Indus and Ganges, all of which are seriously threatened. The freshwater systems they inhabit must be managed with biodiversity as a top priority”.
The population of Ganges river dolphins is estimated at around 3,500 to 4,500 across Bangladesh, India, and Nepal and is still declining. Meanwhile, the Indus dolphins have achieved an impressive recovery over the last 20 years, with numbers going up from approximately 1,200 in 2001 to more than 1,900 in 2017, despite huge challenges including an 80 per cent decline in the extent of their range.
While almost all Indus river dolphins are found in Pakistan, a tiny population still survive in the Beas – a tributary of the Indus – in India.
“The Indus river dolphin recovery in Pakistan is due to decades of dedicated on-the-ground work with authorities and communities and shows what is possible when we work together to conserve them,” said Dr Uzma Khan, Asia Coordinator of the WWF River dolphin initiative.
“Serious challenges still face this incredible species and all other river dolphin populations, but we can save them – and by doing so we’ll save so much more since hundreds of millions of people and countless other species depend on the health of river dolphin rivers.”
Javed Ahmed Mahar, Conservator, Sindh Wildlife Department, said that it was encouraging to note the fruits of long term research are near to harvest.
The final decision on the validity of the new species will be made by the Committee on Taxonomy of the Society for Marine Mammalogy in the next few months.