The otherworldly Indus river dolphin is one of only four species of river dolphins left in the world, and its numbers are falling fast in the Pakistani waterways it calls home.
Now a new study has discovered why: As dams are built to divert river water to irrigate crops, the dolphins have become confined to isolated stretches of waterways.
“The link between the construction of the irrigation barges and depletion of river flow matched very well with the timing and the geographic pattern of dolphin disappearance and was even linked with the speed of disappearance,” said Gill Braulik, a marine mammal specialist with the Wildlife Conservation Society in Tanzania and lead author of the study, which was published Wednesday in the journal PLOS ONE.
Braulik and her colleagues studied reports of where the dolphins lived from as far back as the 1870s, just before the first major dam was built. They then compared the times when dolphins were last seen along certain stretches of river with the dates dams were built.
The research shows that dams have chopped the dolphin’s historical range into 17 separate river sections. The dolphins have disappeared from 10 of those sections, and their range is now a fifth of what it once was.
Only 1,100 individual Indus river dolphins survive, according to the World Wildlife Fund. To locate the remaining dolphins, Braulik’s Pakistani coauthors interviewed local fishermen. They had to find the oldest fishermen in each community, a project in itself.
“Elders are very respected in Pakistan,” said Braulik. “We spoke with some very, very old men, some of whom were wheeled out in wheelchairs to speak to us—others could not get out of bed—and they told us amazing stories of a bygone era.”
The Indus river dolphin is no Flipper: It’s brown and blind, and it has protruding, interlocking teeth. The dolphins ply the muddy Indus River, using echolocation—reflected sound—to find one another and the catfish and carp they eat.
“It evolved much earlier than modern marine dolphins and in fact is more closely related to sperm whales and beaked whales in the ocean than to other marine dolphins,” Braulik said.
Though the Indus river dolphin is in dire straits, Braulik said there’s cause for optimism. A balance between development and conservation is still possible, and she points out that although the dolphin’s range has declined, in parts of the river the animals remain abundant. Moreover, government agencies are working with nonprofit organizations to preserve the dolphin.
“There is a need on the Indus—and on many other rivers where there are competing uses for water—to recognize that sufficient flows are required to maintain basic ecological services, and that will benefit ecology and people,” said Braulik.