Question map
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.
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] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
- [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] Economics, Class IX . NCERT(Revised ed 2025) > Chapter 1: The Story of Village Palampur > Suggested Activity > p. 6
PROVENANCE & STUDY PATTERN
Full viewThis 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.
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?
- Statement 2: Does an increase in the population of crocodiles in rivers contribute to the decline of the Ganges River Dolphin?
- Statement 3: Is accidental entanglement or trapping in fishing nets a cause of mortality and population decline in the Ganges River Dolphin?
- Statement 4: Do synthetic fertilizers and other agricultural chemicals used in crop fields adjacent to rivers contribute to the decline of the Ganges River Dolphin?
- Explicit statement linking construction of barrages and dams to depletion of the dolphin population.
- Directly names dams/barrages as responsible factors for population decline.
- 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.
- 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.
- Explicitly states that an increase in crocodile population is not directly linked to the dolphin decline.
- Uses that conclusion to exclude crocodile population increase from the correct list of causes.
- Explains that crocodiles are part of the ecosystem but their increasing population 'is not a direct' (cause).
- Positions crocodile population increase as not a direct contributor compared with other threats (bycatch, pollution, dams).
- Provides the same multiple-choice framing and marks '1,3 and 4 only' as the correct answer, thereby excluding item 2 (crocodile increase).
- Supports the conclusion that crocodile population increase is not considered a contributing reason in this source's answer key.
Lists specific threats to the Ganges dolphin (pollution, fishing nets, poaching, dams) establishing known drivers of decline and implying other causes would need similar ecological pathways.
A student could compare these known major threats with potential impacts from rising crocodile numbers (e.g., increased mortality, competition) to judge if crocodiles are a plausible additional threat.
Describes gharial (a crocodilian) conservation goals explicitly to increase crocodile population through protection and captive breeding.
One could extend this by checking where gharial/crocodile populations have increased and whether those river stretches overlap with dolphin habitats to test for temporal/spatial correlation with dolphin declines.
States the Indian Crocodile Conservation Project successfully produced large numbers of crocodiles, implying local increases in crocodilian abundance in Indian rivers.
A student can use this to identify when/where crocodile numbers rose and then compare dolphin population trends in the same areas and periods to seek coincidence or lack thereof.
Notes that rivers contain turtles, crocodiles and gharials, confirming spatial co-occurrence of crocodilians and riverine megafauna including potential habitat overlap with dolphins.
Using range maps or river locality data, a student could map overlap zones to assess potential for direct interactions (predation/competition) between crocodiles and dolphins.
States the Ganges river dolphin is an indicator of river ecosystem health, suggesting that changes in other large river fauna or ecosystem structure could correspond with dolphin status.
A student could treat crocodile population increases as an ecosystem change and investigate whether such changes have historically correlated with shifts in dolphin indicators (abundance, distribution).
- Snippet explicitly names 'accidental trapping in fishing nets' as a threat to the Ganges River Dolphin.
- Links this threat to depletion of the dolphin population (mortality/population decline).
- Describes how operation of small-meshed nets and unsustainable fishing practices destroy aquatic biodiversity.
- Provides supporting context that harmful fishing gear can negatively affect river fauna, consistent with entanglement impacts.
- Explicitly states chemical fertilisers applied by farmers may flow into water bodies.
- Links nitrates from fertilisers to eutrophication, which is described as injurious to aquatic ecosystems.
- Identifies river water pollution as a threat to the Ganges River Dolphin.
- Places the dolphin’s decline among causes that include water-quality related factors.
- Notes chemical fertilisers can escape from soil and pollute rivers and lakes, supporting the pathway from fields to waterways.
- Describes broader environmental impacts of continuous chemical fertiliser use that imply harm to aquatic systems.
- Bullet 1. [THE VERDICT]: Sitter. Direct hit from Majid Hussain (Environment & Ecology) or Shankar IAS Chapter on Aquatic Ecosystems.
- Bullet 2. [THE CONCEPTUAL TRIGGER]: 'Threats to Keystone Species'. When studying any National Animal (Tiger, Elephant, Dolphin), you must categorize threats into 4 buckets: Habitat Fragmentation, Poaching, Pollution, and Accidental Mortality.
- Bullet 3. [THE HORIZONTAL EXPANSION]: Memorize these Dolphin facts: 1) IUCN Status: Endangered, 2) CITES: Appendix I, 3) Habitat: Freshwater only (blind, relies on echolocation), 4) Sanctuary: Vikramshila Gangetic Dolphin Sanctuary (Bihar), 5) Sibling species: Indus River Dolphin (Bhulan) and Irrawaddy Dolphin (Chilika - brackish water).
- Bullet 4. [THE STRATEGIC METACOGNITION]: Distinguish between 'Natural Coexistence' and 'Anthropogenic Threats'. Native predators (Crocodiles) and prey (Dolphins) have co-evolved for millions of years; one does not simply cause the decline of the other without human interference. Always look for the human hand in 'Decline' questions.
Reference [1] explicitly links dam/barrage construction to dolphin depletion; [5] outlines general dam impacts on aquatic life.
High-yield for environment and ecology questions: connects infrastructure development to species decline and conservation policy. Useful for essay and mains answers linking development vs conservation trade-offs; study by comparing species-specific examples and mechanisms.
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
- NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 3: The Making of a Global World > p. 57
NCERT [5] notes dams fragment rivers and hinder migration; [9] shows real-world example of water diversion at a barrage.
Frequently tested concept in geography and environment: explains how barriers affect life-cycles of aquatic fauna and river health. Helps answer questions on river connectivity, basin management, and mitigation measures (fish ladders, bypasses); prepare by linking cause–effect instances and policy responses.
- NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 3: The Making of a Global World > p. 57
- Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > River Regimes > p. 23
Reference [5] describes altered flow and sedimentation changes due to dams; [7] discusses sediment retention by reservoirs affecting downstream habitat.
Important for understanding ecological consequences of hydro-projects and for writing balanced answers on water resource projects. Connects to topics on river geomorphology, aquatic ecology and environmental impact assessment; master by studying mechanisms and examples of habitat degradation.
- NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 3: The Making of a Global World > p. 57
- Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 9: Lakes > Lakes and Man > p. 86
Reference evidence explicitly lists primary threats to the Ganges dolphin (pollution, accidental entanglement in fishing nets, poaching, and habitat fragmentation from dams/barrages).
High-yield for UPSC environment/conservation mains and prelims: questions often ask causes of species decline and conservation measures. Connects to freshwater biodiversity, river management, and Project Dolphin. Prepare by memorising major threats, linking to policy responses (anti-poaching, fishing regulations, dam impacts) and practising answer-structuring around threat–impact–remedy.
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 16: Conservation Efforts > 16.13.r. Ganges Dolphin > p. 246
References describe targeted conservation programs aimed to protect and increase crocodile/gharial populations and report recovery efforts.
Useful for questions on species-specific conservation projects and their ecological consequences; connects to human-wildlife conflict, habitat management and protected-species policies. Enables comparative questions (e.g., simultaneous conservation of different river fauna). Study by reviewing project objectives, outcomes and potential ecosystem implications.
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > gharial project > p. 47
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 16: Conservation Efforts > 16.10. INDIAN CROCODILE CONSERVATION PROJECT > p. 244
- CONTEMPORARY INDIA-I ,Geography, Class IX . NCERT(Revised ed 2025) > Chapter 5: Natural Vegetation and Wildlife > WILDLIFE > p. 44
Evidence identifies the Ganges river dolphin as a reliable indicator of the health of the entire river ecosystem.
Concept links species conservation to broader river health and policy measures (pollution control, flow regimes). Frequently useful in analytical UPSC answers linking biodiversity to ecosystem services and environmental governance. Prepare by understanding indicator species concept and examples, and practice integrating with river management topics.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 12: Animal Diversity of India > Ganges river dolphin > p. 189
- Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > Five Confluences in the upper reaches of Ganga > p. 12
The primary reference names accidental trapping in fishing nets as a direct threat; another reference shows small-meshed nets destroy aquatic biodiversity.
High-yield for environment and biodiversity questions: connects fisheries practices to species mortality and population decline. Useful across topics like wildlife threats, bycatch policy, and conservation measures. Prepare by linking specific gear types/practices to ecological outcomes and policy responses (regulation, gear modification, protected areas).
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > ganges dolphin > p. 48
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 6. Commercial Fishing & Aquaculture > p. 47
The 'Next Logical Question' is about 'Noise Pollution' and 'River Traffic'. Since Ganges Dolphins are blind and rely on echolocation (Susu), the development of National Waterway-1 (NW-1) and dredging activities are the specific, high-tech threats currently being debated in policy circles.
Apply the 'Nature doesn't kill Nature' heuristic. In a stable ecosystem, a native predator (Crocodile) does not cause the extinction-level decline of another native apex species (Dolphin). Decline implies a disruption. Options 1, 3, and 4 are human disruptions. Option 2 is nature. Eliminate the natural factor to find the answer.
Link this to GS3 Infrastructure & Economy: The conflict between the 'Jal Marg Vikas Project' (National Waterways) and the 'Project Dolphin'. It is a classic case study for 'Development vs. Conservation' essays involving riverine ecosystems.