Rare sighting Roland Seitre/naturepl.com

Nepal’s endangered river dolphins are in a tangle. Not only can they die in fishing nets, but farmers further threaten their survival by draining rivers for irrigation.

A 15-year study of the Karnali river found that competing demands for river water, especially during the dry winter months, have led to a near halving of this river’s small population of blind Ganges river dolphins (Platanista gangetica gangetica).

In 2010, severe flooding shifted the balance of water flow in a tributary of the Karnali river, from primarily flowing through a protected national park where fishing is restricted, to a region dominated by fishing and agriculture. Water levels in the national park reached below 2 metres – a minimum threshold required to sustain the dolphins. They responded by migrating to the now-deeper waters outside the park.


The unusual event caught the attention of a research team in Nepal and India, led by conservation biologist Gopal Khanal at Nepal’s Tribhuvan University, who investigated how the change in habitat affected the dolphins.

From 2012, the team observed a gradual decline in water levels in both river channels, with no corresponding reduction in rainfall. The decline coincided with efforts to improve irrigation networks in the area, suggesting that the water had been diverted for agriculture.

“Dolphins have adapted to track river depth, but this evolutionary cue landed them in a risky situation,” says Khanal, who describes the situation as an “ecological trap”.

Unprotected waters

The dolphins found themselves in unprotected waters, and as irrigation eventually lowered the water levels, they were more likely to get entangled in fishing nets in their new habitat. “Abstracting more water for irrigation, particularly in the dry season, aggravates existing fishing threats for the river dolphins,” says Khanal.

Between 2012 and 2015, dolphin numbers in the Karnali shrunk from 11 to six; two were found dead in large fishing nets. An estimated 50 dolphins live in Nepal, with up to 4000 in downstream India and Bangladesh, where a similar situation may be unfolding.

“This is an incredibly useful case study,” says Gillian Braulik at the Wildlife Conservation Society in Tanzania. “River systems all over the world, from the Mekong to the Irrawaddy and the Amazon, are facing similar changes; the situation is just more extreme in South Asia.”

In an assessment for the International Union for Conservation of Nature Red List, Braulik found that the Ganges river dolphin and its close relative, the Indus river dolphin, face a range of threats, from the construction of large dams, barrages and irrigation canals, to pollution, fishing and occasional poaching.

In 2012, Braulik documented an 80 per cent decline in the Indus river dolphin’s habitat since the 19th century, primarily due to removal of water for irrigation.

“It is important to maintain a minimum ecological flow to save dolphins from extinction,” says Khanal.

Journal reference: Biological Conservation, DOI: 10.1016/j.biocon.2016.10.026

Read more: New species of river dolphin born of Amazon rapids