India’s first complete survey finds dolphin threats

Source: The post India’s first complete survey finds dolphin threats has been created, based on the article “What the first-ever comprehensive survey of India’s river dolphins found” published in “Indian Express” on 6th March 2025.

UPSC Syllabus Topic: GS Paper3- Environment- Conservation

Context: The article talks about the first complete survey of river dolphins in India. It found 6,324 Gangetic dolphins and only 3 Indus dolphins. The survey showed threats to dolphins from pollution and low water levels, and identified areas with more or fewer dolphins.

What were the main findings of the dolphin population survey in India?

1. Total Population: The survey estimated an average of 6,324 Gangetic dolphins, ranging from 5,977 to 6,688, in the Ganga and Brahmaputra river basins. Only 3 Indus dolphins were found, all in the Beas River in Punjab.
2. State-wise Distribution: Uttar Pradesh had the most Gangetic dolphins (2,397), followed by Bihar (2,220), West Bengal (815), Jharkhand (162), and a combined count of 95 in Rajasthan and Madhya Pradesh.
3. River-specific Findings: In the Ganga’s main stem, 3,275 dolphins were recorded, 2,414 in its tributaries, 584 in Brahmaputra’s main stem, and 51 in its tributaries.
4. Hotspots and Coldspots:

• Hotspot: The Chausa-Manihar stretch in Bihar had the highest density with 2.20 dolphins per km.

Another dense population was found between Manihari in Bihar and Rajmahal in Jharkhand with 2.75 dolphins per km.

• Coldspot: The Narora-Kanpur stretch in Uttar Pradesh had an encounter rate of 0.1 dolphins per km.

How was the survey conducted and what challenges did it face?

1. The survey covered 7,109 km of the Ganga and 1,297 km of the Brahmaputra, including tributaries, and 101 km of the Beas River.

Visual and acoustic methods were used to estimate dolphin numbers.

2. Dolphins surface for 1.26 seconds and dive for 107 seconds, causing observer and availability errors.
3. Hydrophones captured dolphins’ clicks for accurate counts, overcoming observer errors.
4. Different methods were used based on channel width and depth, like the double observer method for wide channels.
5. Challenges included turbid waters, brief surfacing time, and varying river conditions.

What threats do river dolphins face in India?

1. Gangetic and Indus dolphins are endangered and protected under the Wildlife Protection Act, 1972.
2. They face threats from pollution, riverbed mining, low water depth, habitat damage, prey decline, and climate change.
3. Coldspots with few or no dolphins were found in stretches like Narora to Kanpur in the Ganga and in parts of the Yamuna, Sharda, and Rapti rivers.

What are the trends in dolphin populations in Assam’s rivers?

1. In Assam, the main Brahmaputra river has a healthy depth, but its tributaries have low depths, leading to fewer dolphins.
2. The Barak River was a coldspot. The dolphin population in Subansiri and Kulsi rivers is declining, showing a worrying trend for these habitats.

Question for practice:

Discuss the effectiveness of the methods used in the first complete survey of river dolphins in India and the implications of their findings for conservation efforts.