Indus blind dolphin or 'susu' is a river dolphin of Pakistan not found anywhere else in the world .
The Indus River dolphin, locally known as bhulan is an obligate freshwater cetacean species found in the Indus River, Pakistan. A flagship species, this dolphin is an indicator of the biological health of the aquatic and terrestrial environment adjoining the Indus River. It is the second most endangered freshwater dolphin species in the world, the first being the 'functionally extinct' Yangtze River dolphin. The current distribution range of the Indus River dolphin is about a 1,000 km stretch of the Indus River which includes the main Indus channel and active channels connected to it between Jinnah and Kotri barrages.
The existing population of Indus River dolphin is about 1,800 dolphins found between Chashma and Kotri barrages in the Indus River.
The government of Sindh designated a 200 km stretch of the Indus River between Guddu and Sukkur barrages as the Indus Dolphin Reserve in 1974. It is a legally Protected Area with the largest population of Indus River dolphins. It is also an important bird area and an internationally recognised Ramsar site. The reserve was also designated as a Ramsar site because of the presence of a wide spectrum of associated biodiversity.
The Indus River dolphin is characterized by a long beak, rounded belly, stocky body, very small dorsal fin and large flippers. This species is also referred to as the 'blind dolphin' as its eyes haven't developed a lens. It relies on echolocation to find fish, shrimp, and other prey in the bottom mud.
The Indus River dolphin swims on its side, at times enabling it to move in water as shallow as 30 cm. As it swims on its side, it trails a flipper along the bottom of the river. After 30 to 60 seconds, when it needs to breathe, it swims to the surface, rotates upright to take in the air, and then rotates 90 degrees again as it swims back to the bottom. It migrates upstream into the smaller tributaries during the monsoon rains and migrates downstream to the main channels in the dry season.
Threats
The Indus River dolphin was distributed in a wide range, once found in the Indus River and in its major tributaries in Punjab's Sutlej River, Chenab River, Ravi River and Jhelum River, but is now confined to the main channel of the Indus River. Water regulatory barrages constructed on the Indus River are responsible for the highly fragmented population of Indus River dolphins confining it into five sub-populations. Fragmented sub-populations may face hazardous impacts of inbreeding, which can lead to significant loss of genetic diversity. Shortage of water and water diversion to meet agricultural needs of the country resulted in extirpation of Indus River dolphin from upper reaches of the Indus River. Increased days with zero flow downstream of Kotri Barrage restricted dolphin populations from moving further southwards significantly limiting the distribution range.
Accidental mortality of Indus River dolphins is attributed to entanglements in fishing nets as by-catch of fish and unsustainable fishing practices. A large number of mortalities also occured after the devastating flood of 2010. Intensified fishing practices also resulted in the highest mortality in year 2011.