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Q14 (IAS/2014) Environment & Ecology › Biodiversity & Protected Areas › Flagship species ecology Official Key

Other than poaching, what are the possible reasons for the decline in the population of Ganges River Dolphins? 1. Construction of dams and barrages on rivers 2. Increase in the population of crocodiles in rivers 3. Getting trapped in fishing nets accidentally 4. Use of synthetic fertilizers and other agricultural chemicals in crop-fields in the vicinity of rivers. Select the correct answer using the code given below.

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is option C (1, 3, and 4 only).

The Ganga River Dolphin is threatened by river water pollution, accidental trapping in fishing nets and poaching for their oil. Moreover, construction of barrages and dams are also responsible for the depletion of dolphin population.[1] Therefore, statements 1 and 3 are clearly correct reasons for the decline.

Regarding statement 4, dams affect rivers' natural flow causing poor sediment flow and poorer habitats for aquatic life, and they fragment rivers making it difficult for aquatic fauna to migrate[2]. Additionally, chemical fertilizers may escape from the soil and pollute groundwater, rivers and lakes[3], which contributes to the river water pollution mentioned as a threat to dolphins.

However, statement 2 about crocodile population increase is incorrect. The increase in the population of crocodiles is not directly linked to the decline in the Ganges River Dolphins[4]. There is no evidence in the documents supporting crocodiles as a threat to dolphin populations.

Sources
  1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
  2. [2] NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 3: The Making of a Global World > p. 57
  3. [3] Economics, Class IX . NCERT(Revised ed 2025) > Chapter 1: The Story of Village Palampur > Suggested Activity > p. 6
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Q. Other than poaching, what are the possible reasons for the decline in the population of Ganges River Dolphins? 1. Construction of dams a…
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Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 7.5/10 · 2.5/10
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This is a textbook 'Threats to Biodiversity' question found verbatim in standard sources like Majid Hussain and Shankar IAS. It tests your ability to distinguish between human-induced disasters (dams, nets, chemicals) and natural ecological coexistence (crocodiles). It is a high-fairness question rewarding basic reading.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Are construction of dams and barrages on rivers a contributing cause of the population decline of the Ganges River Dolphin?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
Presence: 5/5
“Te Ministry of Environment and Forests notifed the Ganges River Dolphin as the National Aquatic Animal. Dolphin in India is found in the Ganga and Brahmaputra rivers. Te Ganges Dolphin is among the four 'obligate' freshwater dolphins found in the world. Te other three fresh water dolphin are (i) Baiji (Yangtze Kiang), (ii) the 'Bhulan' of the Indus (Pakistan), and the 'Boto' of the Amazon River. Tese four species live either in rivers or in lakes. Te Ganga River Dolphin is threatened by river water pollution, accidental trapping in fshing nets and poaching for their oil. Moreover, construction of barrages and dams are also responsible for the depletion of dolphin population.”
Why this source?
  • Explicit statement linking construction of barrages and dams to depletion of the dolphin population.
  • Directly names dams/barrages as responsible factors for population decline.
NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 3: The Making of a Global World > p. 57
Presence: 4/5
“In recent years, multi-purpose projects and large dams have come under great scrutiny and opposition for a variety of reasons. Regulating and damming of rivers affect their natural flow causing poor sediment flow and excessive sedimentation at the bottom of the reservoir, resulting in rockier stream beds and poorer habitats for the rivers' aquatic life. Dams also fragment rivers making it difficult for aquatic fauna to migrate, especially for spawning. The reservoirs that are created on the floodplains also submerge the existing vegetation and soil leading to its decomposition over a period of time. Sardar Sarovar Dam has been built over the Narmada River in Gujarat.”
Why this source?
  • Explains mechanisms by which dams/regulation harm aquatic life: altered flow, poor sediment transport, degraded habitats.
  • Specifically notes fragmentation that impedes aquatic fauna migration, a key effect relevant to river dolphins.
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > River Regimes > p. 23
Presence: 3/5
“This is largely due to the water supply from the Himalayan snow-melt. The discharge data, however, do not include the volume of water diverted for irrigational purposes at different points before the Farakka Barrage (Malda, West Bengal). The mean maximum discharge of the Ganga at Farakka is about 55,000 cusecs, while the mean minimum is only 1300 cusecs. The two peninsular rivers display an interesting difference in their regime as compared to the Himalayan rivers. The Narmada has a very low volume of discharge from January to July. It suddenly rises in August when the maximum discharge is attained. The fall in October is as spectacular as the rise in August.”
Why this source?
  • Documents river discharge changes and water diversion before the Farakka Barrage, showing how barrages alter river regimes.
  • Provides context that large barrages affect river flow volumes — a factor that can impact species dependent on flow dynamics.
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Statement analysis

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Statement analysis

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