Previous Year Question
Other than poaching, what are the possible reasons for the decline in the population of Ganges River Dolphins?
Construction of dams and barrages on rivers
Increase in the population of crocodiles in rivers
Getting trapped in fishing nets accidentally
Use of synthetic fertilizers and other agricultural chemicals in crop-fields in the vicinity of rivers
Which of the statements given above are correct?
1 and 2
2 and 3
1, 3 and 4
All of the above
Correct Answer: C
Detailed Solution
The scientific name of the Ganges River Dolphin is Platanista gangetica gangetica.
It is a freshwater dolphin found mainly in the Ganga-Brahmaputra-Meghna river system.
It has been declared the National Aquatic Animal of India.
Its eyesight is extremely weak, and it uses echolocation to navigate and capture prey.
Dams and barrages alter the natural flow regime of rivers.
These structures can divide dolphin populations into small and isolated groups and obstruct their movement.
Changes in water depth, flow, sediment and fish availability can also affect dolphin habitats.
Therefore, Statement 1 is correct.
An increase in the number of crocodiles in a river is not regarded as a major established cause of the decline of the Ganges River Dolphin population.
Therefore, Statement 2 is incorrect.
Dolphins may become accidentally entangled in fishing nets and drown because they cannot reach the surface to breathe.
This unintended capture is known as bycatch; therefore, Statement 3 is correct.
Synthetic fertilizers, pesticides and other agricultural chemicals carried by runoff from fields can pollute river water.
These pollutants can affect dolphins, their reproductive capacity and their prey species; therefore, Statement 4 is correct.
Hence, the construction of dams and barrages, accidental entanglement in nets and pollution by agricultural chemicals are the correct causes.