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Population of the endangered Indus River dolphin is declining as more water is being used for irrigation and more part of the river is fragmented, according to a new study. 

Researchers used historical range data and information on dolphin presence from fisher interviews to develop the understanding of the timing pattern of range decline of the Indus River Dolphin. 

According to the World Wildlife Fund, dolphins originated in the ancient Tethys Sea, but when it dried up 50 million years ago, they were forced to adapt to rivers to survive. As of now, only about 1,100 dolphins exist in the lower parts of the Indus River in Pakistan. Most of them are confined to a 750-mile stretch of the river as well as divided into isolated populations by six barrages. 

To figure out what exactly is causing their decline, the study considered parameters such as 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. 

According to findings, the historical range of the Indus dolphin has been fragmented into 17 river sections by diversion dams.

"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 the Wildlife Conservation Society in a statement. 

"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 study has been published in the journal PLOS ONE.