River Dolphin on the Decline Due to Dams

Populations of the endangered Indus river dolphin are on the decline in part from the removal of river water for irrigation and habitat fragmentation, a new study has warned.

Many freshwater marine mammals are endangered due to rapidly degrading habitat, and conservation depends on preserving what habitat is left.

Gill Braulik from the Wildlife Conservation Society along with colleagues from the University of St. Andrews used historical range data and information on dolphin presence from fisher interviews to better understand the timing pattern of range decline of the Indus River Dolphin, an endangered freshwater dolphin that inhabits one of the most modified rivers in the world.

The dolphins are believed to have originated in the ancient Tethys Sea, but when it dried up 50 million years ago they were forced to adapt to rivers to survive, according to the World Wildlife Fund. Only about 1,100 exist today in the lower parts of the Indus River in Pakistan, and are mostly confined to a 750-mile stretch of the river as well as divided into isolated populations by six barrages.

In order to figure out the reasons behind their decline, researchers considered the date of construction of the nearest dam, dry season river discharge, distance from the edge of the former range and length of river section.

Results indicate that the historical range of the Indus dolphin has been fragmented into 17 river sections by diversion dams.

River dolphins disappeared from ten river sections, still live in the six areas mentioned above, and are of unknown status in one section.

Low dry-season river discharge, due to irrigation at diversion dams, is mainly to blame for their declining population and decreased habitat.

"This important study shows that it is river habitat fragmentation by dams, and removal of river water for irrigation that has caused the massive range decline of the Indus River freshwater dolphin," Braulik said in a statement.

This research is also important in understanding how marine animals cope with dams and habitat loss, because unfortunately dam construction is not going to stop.

"This increased understanding of species decline in fragmented river systems is especially important because hundreds of new dams and water developments are planned or are under construction in many of the world's rivers and large losses of aquatic biodiversity can be expected."

The findings were published in the journal PLOS ONE.