Dramatic decline in Indus river dolphins, irrigation and habitat fragmentation to blame

17 July 2014, 4:48 pm EDT By Rebecca Kaplan Tech Times
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A decline in river dolphin population may be due to river fragmentation caused by dams, a new research paper says.  ( )

Indus river dolphins may be in danger due to irrigation dams along the river that fragment the water supply, according to new research.

Conservationists have long thought that dams built along major rivers would wreak havoc on the marine life and ecosystems there, and this research proves that they may have been right.

Gill Braulik, a cetacean specialist at the Wildlife Conservation Society in Tanzania, who led the writing of this new study, said in a statement, "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." He added, "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."

River dolphins originally evolved from pre-cursors that lived in the seas but were edged out of the oceans by other species of marine dolphins and adapted to life in the rivers. There are only a few species of river dolphins worldwide.

Many species of river dolphins are endangered or critically endangered, according to the International Union for Conservation of Nature. One species, the Yangtze River dolphin, has most likely been extinct since the mid-2000s, according to the new research paper.

According to the new research paper, scientists think fragmentation of the water caused by dams may be to blame for this decline in river dolphin populations. The Indus River, for example, where the Indus River dolphin lives, is covered with dams that draw hydroelectric power from the river and use irrigation to drain water to other sources. These dams segment the river. The researchers studied data, including the dates of dam construction, water flow during the dry season, and distance from the edge of the former range and length of river section to form their findings. Braulik tracked reports of the river dating back to the 1870s, before major dams were build along the river, and found that the part of the river where the dolphins lived has been broken up into 17 pieces since 1870. In six of those sections, the dolphin population has disappeared; in one, the status is unknown. Only 10 sections of the river still contain dolphins today.

The dolphins probably disappeared from those sections due to low water supply during the dry season, which resulted from damming and irrigation along the river, the paper said.

A 2012 paper in the journal of Proceedings of the National Academy of Sciences showed that these separate species of river dolphins evolved similar features independently of each other, such as having longer snouts than oceanic dolphins, and having worse eyesight. World Wild Fund for Nature speculates that the bad eyesight may have evolved that way because good eyesight isn't necessary in dark, cloudy river water.

The paper said, "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."



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