The correct answer is option 1, Gulf of Mannar. The Gulf of Mannar is a bioregion located between southeastern India and western Sri Lanka. It is a designated biosphere reserve known for its rich marine biodiversity. The Dugong, also known as the sea cow, is found in this area. The Gulf of Mannar is home to a variety of marine ecosystems including coral reefs, seagrass beds, and mangrove forests, which provide a suitable habitat for the Dugong. Nokrek (option 2) is a national park in Meghalaya, Manas (option 3) is a national park in Assam, and Sundarban (option 4) is a mangrove forest in the Bay of Bengal. Although these sites are important for conservation, the Dugong is not found there.