Question

UPSC Prelims 2014 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

Select the correct answer using the code given below:

1. 1 and 2 only
2. 2 and 3 only
3. 1, 3 and 4 only
4. 1, 2, 3 and 4

Answer (Detailed Solution Below)

Option 3: 1, 3 and 4 only

Detailed Solution

Explanation:

Ganges river dolphins are divided into isolated groups because of the construction of more than 50 dams and other irrigation-related projects. This makes them susceptible to inbreeding as they cannot move to new areas. Dolphins trapped above a dam are exposed to poaching, especially during dry summer months. Dolphins below a dam are threatened by heavy pollution, increased fishing activities and vessel traffic. They also have less food because dams disturb the migration, breeding cycles and habitat of fish and other prey. So, point 1 is correct.
The crocodile population has nothing to do with the decline in the population of dolphins. It is human activities that are mainly responsible. So, point 2 is not correct.
The habitat of the Ganges river dolphin is within one of the most densely populated areas of the world. Ganges river dolphins and people both favor areas of the river where fish are plentiful and the water current is slower. As a result more dolphins die because of being accidentally caught in the fishing nets, also known as bycatch. The Ganges river dolphin is still hunted for meat and oil, which are both used medicinally. So, point 3 is correct.
Each year, 9,000 tons of pesticides and 6 million tons of fertilizers are used in the vicinity of the river. High levels of pollution can directly kill prey species and dolphins, and completely destroy their habitat. As the top predator, river dolphins have been known to have high levels of persistent toxic chemicals in their bodies, which is likely to adversely affect their health. So, point 4 is correct.

Therefore, option (3) is the correct answer.

Knowledge Box

The Ganges River dolphin was officially discovered in 1801. Ganges river dolphins once lived in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Nepal, India, and Bangladesh. But the species is extinct from most of its early distribution ranges.
The Ganges river dolphin can only live in freshwater and is essentially blind. They hunt by emitting ultrasonic sounds, which bounce off of fish and other prey, enabling them to “see” an image in their mind. They are frequently found alone or in small groups, and generally, a mother and calf travel together.

Subject: Environment | Biodiversity and Conservation

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