Other than poaching, what are the possible reasons for the decline in the population of Gangas 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.
Contents18
- A1 and 2 only
- B2 and 3 only
- C1, 3 and 4 only
- D1, 2, 3 and 4
Show answer
Answer: (C) 1, 3 and 4 only
The Gangetic River Dolphin (India's national aquatic animal) is declining due to multiple human-caused threats:
(1) Dams and barrages — CORRECT: They fragment the river, isolate dolphin populations, reduce water flow, and block migration routes.
(2) Crocodile population increase — WRONG: Crocodiles are NOT a significant threat to dolphins. Both have coexisted for millennia. Dolphin decline is human-caused, not predator-caused.
(3) Fishing nets — CORRECT: Dolphins accidentally get entangled in gill nets and drown (bycatch).
(4) Agricultural chemicals — CORRECT: Pesticides, fertilizers, and industrial effluents from nearby fields poison the river water, reducing fish populations (dolphin food) and directly harming dolphins.
Statements 1, 3, and 4 are correct. The crocodile option is the distractor.
The Gangetic River Dolphin is India's national aquatic animal and is endangered, making it a priority conservation topic for UPSC.
The question tests whether students can distinguish between real human-caused threats versus natural predation - crocodiles and dolphins have coexisted for millennia without causing population decline.
UPSC is checking if students understand the full impact chain of river development projects, agricultural runoff, and fishing practices on aquatic ecosystems.
Gangetic River Dolphin
Environment Gangas River Dolphins national aquatic animal
Gangetic River Dolphin: India's National Aquatic Animal
India's national aquatic animal since 2009
Found only in Ganga-Brahmaputra-Meghna river systems
Classified as Endangered by IUCN
Functionally blind - uses echolocation to navigate
The Gangetic River Dolphin (Platanista gangetica) is a freshwater dolphin endemic to South Asian river systems. Unlike marine dolphins, it has adapted to murky river waters and relies entirely on echolocation for hunting fish and navigation.
Key Characteristics
Feature | Description |
|---|---|
Scientific Name | Platanista gangetica |
Habitat | Freshwater rivers - Ganga, Brahmaputra, Meghna |
Vision | Functionally blind - eyes lack lenses |
Navigation | Echolocation using ultrasonic sounds |
Diet | Fish, shrimp, crustaceans |
Conservation Status | Endangered (IUCN Red List) |
Gangetic Dolphin Habitat
Source: Drishti IAS — Gangetic Dolphins · www.drishtiias.com
Threats to River Dolphins
Environment decline in the population dams and barrages fishing nets synthetic fertilizers agricultural chemicals
Human Threats Causing Dolphin Population Decline
Habitat fragmentation by dams blocks dolphin movement
Bycatch in fishing nets causes accidental deaths
Chemical pollution reduces fish populations and harms dolphins
Sound pollution from boats interferes with echolocation
Major Threats Analysis
Threat | Impact on Dolphins | Correct/Incorrect |
|---|---|---|
Dams & Barrages | Fragment habitat, block migration, reduce water flow | CORRECT |
Fishing Net Bycatch | Accidental entanglement leads to drowning | CORRECT |
Agricultural Chemicals | Poison water, reduce fish prey, bioaccumulation | CORRECT |
Crocodile Predation | Natural coexistence - not a significant threat | INCORRECT |
The question tests understanding of anthropogenic vs natural threats. Crocodiles and dolphins have coexisted for millennia - the real threats come from human activities disrupting river ecosystems.
Trap: Crocodiles as dolphin threat - they naturally coexist, decline is human-caused
Remember: All correct options involve human activities - dams, nets, chemicals
Key distinction: Natural predators ≠ population decline causes in UPSC context
Dam Impacts on River Ecosystems
Environment dams and barrages rivers
How Dams Fragment Aquatic Ecosystems
Dams create physical barriers blocking fish and dolphin movement
Habitat fragmentation isolates populations genetically
Altered water flow patterns affect breeding and feeding
Dam Impact Chain
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Dam Construction**
Physical barrier across river`"]
s2["`**Habitat Fragmentation**
River divided into isolated segments`"]
s3["`**Migration Disruption**
Dolphins cannot move between segments`"]
s4["`**Population Isolation**
Genetic isolation and reduced breeding`"]
s5["`**Population Decline**
Smaller, isolated groups face extinction risk`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Specific Impacts on Dolphins
Water flow reduction concentrates pollutants and reduces oxygen levels
Sedimentation changes alter riverbed structure and fish habitat
Temperature changes in reservoir water affect aquatic food webs
Noise from construction interferes with dolphin echolocation systems
Bycatch in Fisheries
Environment fishing nets accidentally
Bycatch: Accidental Capture of Non-Target Species
Bycatch = accidental capture of non-target species in fishing gear
Gill nets are particularly dangerous for dolphins
Dolphins drown when trapped underwater in nets
Bycatch occurs when dolphins accidentally swim into fishing nets while hunting for fish. Since dolphins are air-breathing mammals, they drown if trapped underwater for more than 10-15 minutes.
Types of Fishing Gear & Dolphin Risk
Fishing Method | Risk Level | Why Dangerous |
|---|---|---|
Gill Nets | Very High | Fine mesh traps dolphins by gills/fins |
Trawl Nets | High | Large nets can engulf swimming dolphins |
Hook & Line | Low | Minimal entanglement risk |
Fish Traps | Medium | Dolphins may enter chasing fish |
Conservation Solutions
Dolphin-safe fishing gear with escape hatches or acoustic deterrents
Fishing zone regulations in known dolphin habitats
Alternative livelihoods for fishing communities
Real-time monitoring of dolphin locations to avoid fishing
Agricultural Pollution in Rivers
Environment synthetic fertilizers agricultural chemicals crop-fields
How Agricultural Chemicals Poison River Ecosystems
Fertilizer runoff causes eutrophication and oxygen depletion
Pesticides accumulate in fish tissues, poisoning dolphins
Bioaccumulation concentrates toxins up the food chain
Pollution Pathway
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Chemical Application**
Fertilizers/pesticides used on crops`"]
s2["`**Surface Runoff**
Rain washes chemicals into rivers`"]
s3["`**Water Contamination**
Rivers carry dissolved chemicals downstream`"]
s4["`**Aquatic Uptake**
Fish absorb chemicals through gills/food`"]
s5["`**Bioaccumulation**
Toxins concentrate in dolphin tissues`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Chemical Types & Effects
Chemical Type | Source | Impact on Dolphins |
|---|---|---|
Nitrogen Fertilizers | Crop fields | Eutrophication → oxygen depletion → fish kills |
Phosphorus Fertilizers | Agricultural runoff | Algal blooms → habitat degradation |
Organochlorines | Pesticides | Bioaccumulation → reproductive failure |
Heavy Metals | Industrial agriculture | Neurological damage, immune suppression |
Specific Impacts
Reduced fish populations due to water toxicity limits dolphin food supply
Immune system suppression makes dolphins vulnerable to diseases
Reproductive problems including birth defects and reduced fertility
Behavioral changes as toxins affect nervous system function
Dolphin Conservation in India
Environment
India's Dolphin Conservation Initiatives
Project Dolphin launched in 2020 for conservation
Vikramshila Sanctuary in Bihar - first dolphin sanctuary
Protected under Schedule I of Wildlife Protection Act
Conservation Programs
Initiative | Year | Focus Area |
|---|---|---|
Project Dolphin | 2020 | Comprehensive conservation strategy |
Vikramshila Sanctuary | 1991 | 50 km stretch of Ganga in Bihar |
National Aquatic Animal Status | 2009 | Legal recognition and protection |
Ganga Action Plan | 1986 | River cleaning for habitat restoration |
Current Challenges
Population estimate: Only 2,500-3,000 dolphins remain in Indian rivers
Habitat loss: Over 50% decline in suitable river stretches since 1980s
Illegal fishing: Continued use of banned fishing methods in dolphin areas
River pollution: Industrial and agricultural waste overwhelms conservation efforts
Don't confuse: Gangetic dolphins are freshwater only - not marine dolphins
Remember: Conservation focuses on river health, not just dolphin protection
UPSC loves: Project Dolphin details, sanctuary locations, population numbers