Why in news?

Prime Minister Narendra Modi released the results of India's first comprehensive population estimation of riverine dolphins.

Conducted between 2021 and 2023 across the Ganga and Brahmaputra basins, the survey estimated an average of 6,324 Gangetic dolphins. Only three Indus River dolphins were found in the Beas River, Punjab.

The study highlights threats to these endangered species, including pollution, habitat damage, prey decline, and climate change. Both species are accorded the highest protection under the Wildlife Protection Act, 1972.

What’s in today’s article?

• Key Findings of the Riverine Dolphin Survey (2021-2023)
• Survey Methodology and Challenges
• Dolphin ‘Hotspots’ and ‘Coldspots’

Key Findings of the Riverine Dolphin Survey (2021-2023)

• This first-of-its-kind survey provides crucial insights into the status of endangered riverine dolphins and highlights the need for conservation efforts.
• Survey Overview
  • Conducted by the Wildlife Institute of India under the Union Environment Ministry.
  • Covered 28 rivers by boat and 30 rivers by road across the Ganga, Brahmaputra, and Beas River basins.
  • Surveyed 7,109 km of the Ganga and its tributaries, 1,297 km of the Brahmaputra system, and 101 km of the Beas River.
• Dolphin Population Estimates
  • Total Gangetic dolphins: 6,324 (range: 5,977 to 6,688).
  • Ganga’s main stem: 3,275
  • Ganga’s tributaries: 2,414
  • Brahmaputra’s main stem: 584
  • Brahmaputra’s tributaries: 51
  • Indus River dolphins: Only 3, found in the Beas River, Punjab.
• State-wise Distribution of Gangetic Dolphins
  • Uttar Pradesh – 2,397 (highest population).
  • Bihar – 2,220.
  • West Bengal – 815.
  • Jharkhand – 162.
  • Rajasthan & Madhya Pradesh – 95.
  • Punjab – 3.

Survey Methodology and Challenges

• Challenges in Dolphin Population Estimation
  • River dolphins live in turbid, opaque waters and surface only briefly, making population estimation difficult.
  • Dolphins surface for only 1.26 seconds and dive for 107 seconds, leading to:
    • Observer error – Some surfacing dolphins may be missed.
    • Availability error – Some dolphins may not surface during the counting period.
• Survey Techniques
• Visual Surveys
  • Double Observer Method (for deep and wide channels):
  • Two teams positioned on different decks scan both sides of the vessel.
  • The boat travels at 8-10 km/hour to prevent double counting.
• Tandem Method (for channels <600m wide, <3m deep).
• Single Boat Method (for channels <300m wide, <2m deep).
• Acoustic Surveys
  • Uses underwater microphones (hydrophones) to detect dolphin echolocation clicks.
  • Dolphins, being functionally blind, navigate using echolocation.
  • Multiple hydrophones help triangulate dolphin locations and reduce observer error.
• This multi-method approach improves accuracy in estimating the endangered dolphin population.

Dolphin ‘Hotspots’ and ‘Coldspots’

• Coldspots – Areas with Low or No Dolphin Presence
  • Ganga River:
    • Narora to Kanpur (366 km) – Extremely low encounter rate (0.1 dolphins/km).
    • Farukkhabad-Kannauj (between Narora and Kanpur barrages) – Another coldspot.
  • Other Coldspots:
    • Yamuna River (Kaushambi-Chitrakoot).
    • Sharda River (Pilibhit).
    • Rapti River (Balrampur-Siddharth Nagar).
    • Barak River (Assam).
    • Declining dolphin population in Subansiri and Kulsi rivers (Assam).
• Hotspots – Areas with High Dolphin Population
• Uttar Pradesh – Encounter rate of 0.62 dolphins/km.
• Bihar – Highest encounter rate of 1.62 dolphins/km, attributed to deeper river channels and tributary confluences (Ghaghara, Gandak, Kosi, Son).
• Densely Populated Stretches:
  • Chausa-Manihar (590 km) – 2.20 dolphins/km.
  • Manihari (Bihar) to Rajmahal (Jharkhand) – 2.75 dolphins/km (highest density).
  • Assam – Despite deep water in the Brahmaputra, its tributaries had low average depth, affecting dolphin population.
• The survey highlights the influence of river depth and habitat conditions on dolphin distribution, identifying key areas for conservation efforts.