Bangladesh has established three new wildlife sanctuaries for endangered freshwater dolphins in the world's largest mangrove ecosystem, the Sundarbans.

The Ganges River dolphin, known as shushuk in Bangladesh. [Bangladesh Cetacean Diversity Project]

The sanctuaries are intended to protect the last two remaining species of freshwater dolphins in Asia - the Ganges River dolphin, Platanista gangetica gangetica, and the Irrawaddy dolphin, Orcaella brevirostris.

While there is no global population estimate for either species, both have disappeared from major portions of their range but still survive in the Sundarbans. Rough estimates indicate populations of about 225 Ganges River dolphins and 450 Irrawaddy dolphins there.

The Ganges River dolphin?is listed?as Endangered and the Irrawaddy dolphin as Vulnerable to extinction, according to Threatened Species lists of the International Union for the Conservation of Nature and Natural Resources (IUCN).

Freshwater dolphins are among the most threatened animals on Earth because human activities, such as dam construction, toxic contamination and unsustainable fisheries, disturb their habitat. Population surveys find Ganges River and Irrawaddy dolphins living in the very waterways where human activities are most intense.

The three sanctuaries - in the Dhangmari, Chandpai and Dudhmukhi areas of the Eastern Sundarbans mangrove forest - safeguard 19.4 miles (31.4 km) of watery channels with a total area of 4.1 square miles (10.7 sq km).

The newly-protected areas were identified as dolphin hotspots by the Bangladesh Cetacean Diversity Project (BCDP), a project of the Bronx Zoo-based Wildlife Conservation Society.