Gangetic dolphins need deep water; minimal disturbance: Project Dolphin report
The survey under Project Dolphin was carried out by the Union environment ministry along with Wildlife Institute of India (WII) and other organisations
Dolphins thrive in areas with sufficient water depth and minimal anthropogenic disturbances, a first ever population estimation of river dolphins in India by the Union government stated.
The survey under Project Dolphin was carried out by the Union environment ministry along with Wildlife Institute of India (WII) and other organisations.
Under Project Dolphin, India completed a survey of river dolphins across eight states covering the entire range of the Ganges River dolphin in the Ganga and Brahmaputra, as well as the Indus River dolphin in the Beas River systems.
The population estimate reveals 6,324 Ganges River dolphins and only 3 Indus River dolphins, the report released by Prime Minister Narendra Modi on Monday said.
“The results suggest that dolphins thrive in areas with sufficient water depth and minimal anthropogenic disturbances,” the report stated.
India is home to 90% of Ganges River dolphin population which is “endangered”, according to the International Union for Conservation of Nature (IUCN).
Another significant finding of the survey is that they prefer tributaries, confluences, meanders, and mid-channel Islands.
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River dolphins surface for a very limited time, with an average of 1.26 seconds above water, and an average of 107.3 seconds underwater, making it very difficult to observe.
“Given the very low surfacing time, traditional monitoring and abundance estimation methods are difficult to implement. Having a pulse on the abundance and population trends is essential for effective conservation actions for the long-term survival of any species. Especially for dolphins, which inhabit the most threatened habitat in the world, and have a slow growth rate, stemming any population decline in its early stages will be crucial for its survival,” the report states.
According to a separate note by WII on its website, Gangetic dolphins are threatened by unintentional killing through entanglement in fishing gear; habitat destruction due to development projects (for instance, water extraction and the construction of barrages, high dams and embankments), pollution (industrial waste and pesticides, municipal sewage discharge and noise from vessel traffic). Fragmented populations created by dams and barrages have degraded downstream habitat and created impoundments with high sedimentation and altered assemblages of fish and invertebrate species.
In the mainstem of Ganga, the population is estimated to be around 3,275 with an encounter rate of 1.3/km between Bijnor barrage and Ganga Sagar in West Bengal.
Historically, the distribution range of Ganges River Dolphins was seen right from the foothills of the Himalayas downstream of Haridwar to the delta region of Sundarbans. This range has drastically declined significantly.
For instance, in Uttar Pradesh, a total of 3,453km was surveyed covering mainstream Ganga and its tributaries (Chambal, Yamuna, Rapti, Sharda, Geruwa-Kauriala, Ghaghara and part of Gandak River).
The total population of Ganges River Dolphins was estimated to be 2,397 with an encounter rate of 0.69/km.
The highest encounter of dolphins in this stretch was found in the 47km stretch of Bhind-Pachhnada (2.68/km) in the Chambal River followed by Kanpur-Vindhyanchal (1.89/km). National Chambal Sanctuary, Hastinapur Wildlife Sanctuary and Katerniaghat Wildlife Sanctuary are important conservation sites. While dolphin population between Bijnor to Narora Barrage is small, the population between Narora to Kanpur (366 km) is almost non-existent, with an encounter rate of 0.1/km, the report states speculating that this may be due low depth of water there.
The stretches of river where the distribution of dolphins is very sparse or even absent are termed as ‘Coldspots’.
In the Ganga River, such an area was present in the Farukkhabad-Kannauj which lies between the Narora Barrage and Kanpur Barrage. Similar ‘coldspots’ were found in the Yamuna River, from Kaushambi-Chitrakoot, in the Sharda River, in Pilibhit, and in Rapti River, from Balrampur-Siddharth Nagar.
There are no ‘coldspots’ in Bihar. The Ganga River flowing through Bihar also supports a relatively healthy status of associated species, with records of the Vulnerable Smooth-Coated Otter and 81 species of birds including the Endangered Greater Adjutant and Black-bellied Tern.
In West Bengal, Ganges River Dolphin abundance is higher in lower reaches where the Rupnarayan meets the Hooghly. Barak river is identified as the cold spot in the entire state of Assam. The dolphin populations in Subansiri and Kulsi are declining (when compared with previous population estimates). Kaziranga and Orang Tiger Reserves and confluences of tributaries with Brahmaputra are important dolphin areas as per the report.
A total of 536km of Yamuna was also covered by the survey in Uttar Pradesh, starting from Yamuna Setu at Etawah and ending at the Sangam Ghat at Prayagraj. The Ganges River Dolphin were largely observed around Chambal and Yamuna Confluence with a total of 104 (96-112) individuals with an encounter rate of 0.2/Km. The survey underlined that there are several coldspots in Yamuna and only population may be in the Chambal stretch.
In the past, it was reported that the Yamuna had an abundance of river dolphins. Anderson (1878) in his expedition mentions that the river dolphin in the Yamuna could be found as upstream as Delhi. However, this is not the case today, and the last Ganges River Dolphin was recorded from the capital in 1967, the report states.
The survey in 2022 recorded only three Indus River Dolphins, two adults and one neonate.
Unfortunately, Punjab Forest Department reported the death of one adult female dolphin (pregnant with a calf) in March 2024. Thus, the current population is likely to be only two individuals. The Beas conservation Reserve is an important area.
The numbers of Ganges River Dolphins were reported to lie somewhere between 4,000 and 5,000 towards the end of the 20th century. This was later reported to have dropped to 1,800 individuals including the population in the river tributaries by the beginning of the 21st century, and more recently, various guestimates report the population to be between 3,500- 4,500 dolphins. India is home to more than 90% of the Ganges River Dolphins existing in the world, the report adds.