Correct Option
The correct option is (a) 1 only.
Explanation
The Gangetic River Dolphin (Platanista gangetica), locally known as "Susu" due to the sound it produces when breathing, is the National Aquatic Animal of India. It is a freshwater species inhabiting the river systems of the Indian subcontinent.
Statement-wise Analysis
- Statement 1 is Correct: The Gangetic River Dolphin is endemic to the fresh waters of the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of India, Nepal, and Bangladesh. It requires deep water for survival.
- Statement 2 is Incorrect: The Gangetic River Dolphin is essentially blind. It lacks a crystalline lens in its eyes and can only detect the direction of light. It navigates and hunts using echolocation (ultrasonic sounds), not vision. Consequently, it is often referred to as the "blind dolphin," not the "sighted dolphin."
- Statement 3 is Incorrect: The population of the Gangetic River Dolphin is declining, not increasing. Major threats include habitat fragmentation due to dams and barrages, indiscriminate fishing, and heavy pollution from industrial waste and agricultural runoff. Being an indicator species, its presence signals a healthy river ecosystem, while pollution drives its numbers down.
Key Takeaway: The "Susu" or Gangetic River Dolphin is a blind, freshwater mammal found in the Ganga-Brahmaputra system that relies on echolocation for navigation and is threatened by river pollution and habitat fragmentation.