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.

The correct answer is C. Statements 1, 3 and 4 are recognised threats to the Gangetic dolphin (Platanista gangetica), and statement 2 is not.

• Statement 1 is correct. Barrages and dams fragment the river into isolated stretches, blocking the dolphin's movement, breeding and feeding. Reduced flow in dry-season stretches adds to the damage.
• Statement 2 is wrong. Crocodiles do not prey on dolphins in any significant way, and their rising numbers are not a recognised cause of dolphin decline. This rules out D.
• Statement 3 is correct. Dolphins get entangled in gillnets and trawl nets as bycatch. This is a major cause of death, separate from deliberate hunting.
• Statement 4 is correct. Runoff of fertilisers, pesticides and industrial effluents degrades water quality, harms the fish base and affects the dolphins directly.

Core concept: anthropogenic threats to a freshwater cetacean. This is why the species is listed as Endangered and placed in Schedule I of the Wildlife (Protection) Act, 1972. Mains link: river connectivity, environmental flows and the Namami Gange programme.

Trap: picking D because all four sound environmental, without checking whether crocodiles are a real threat to dolphins.