To quantify this habitat fragmentation and assess whether it had harmed the dolphins, Braulik and her colleagues, in partnership with World Wide Fund-Pakistan and the University of St. Andrews in Scotland, studied reports of river-dolphin distribution from the 1870s — just before the first major dam was built — up to the present. They tracked the times when dolphins were last seen in certain river regions, and compared those times to when dams were built, along with water-flow levels during the dry season.
They found that the dolphins' habitat, which was once one large stretch along the Indus River, had been broken up into 17 segments over the years. The dolphins still live in six of those segments, but have disappeared from 10 others, with their status in one segment remaining unknown, the researchers found.
In addition, low water flow during the dry season — a result of damming the river and shunting its flow to irrigate crops — was probably what caused the river dolphins to disappear from much of their range, the researchers said. The dolphins also seemed to do best in the core area of the river, possibly because more dams dot the edges of their range.
The findings provide more comprehensive evidence of what conservationists have long suspected, said Randall Reeves, a cetacean researcher at the International Union for Conservation of Nature who was not involved in the study.
"One could think of the Indus as a 'poster child' showing the destructiveness of water development, especially in an arid environment like Pakistan's," Reeves wrote in an email to Live Science.
Although dolphins have managed to persist, the biodiversity that existed before massive water projects is just a distant memory, he added.
There's no telling whether the new study will impact policy, "but at least the documentation is now available," Reeves said.
The findings were published today (July 16) in the journal PLOS ONE.
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