"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," said Gill Braulik from University of St. Andrews in Britain.
Many freshwater marine mammals are endangered due to rapidly degrading habitat and conservation of these megafauna species depends on maintaining intact habitat.
This study 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.
Additionally, the researchers modelled seven potential explanations for declining range, including date of construction of the nearest dam, dry season river discharge, distance from the edge of the former range and length of river section to identify the factors responsible for the decline.
The historical range of the Indus dolphin has been fragmented into 17 river sections by diversion dams, the findings showed.
River dolphins disappeared from ten river sections, still live in six, and are of unknown status in one section.
Low dry-season river discharge, due to irrigation at diversion dams, was the principal factor that explained the dolphin's range decline, according to the study.
The study appeared in the journal PLOS ONE.