'Tech ears' hear Bangladesh's rare dolphins

A breakthrough in conservation technology pierced the surface of the Jamuna River in Bangladesh in January, in the search for an elusive ecological mystery.

A team of Chinese and Bangladeshi scientists made use of a China-made real-time acoustic monitoring system — dubbed "tech ears" — to detect 146 Ganges River dolphins.

The Jamuna, known as the Brahmaputra in India or Yarlung Tsangpo in China, is a major water channel that forms the delta alongside the Ganges.

The survey provided one of the most comprehensive population snapshots to date of a species long considered nearly "invisible" to the human eye.

The Ganges River dolphin, a freshwater mammal classified as endangered by the International Union for Conservation of Nature, has inhabited the region's murky sediment-heavy waters for millennia. The dolphins are effectively blind, and so navigate and hunt almost exclusively using echolocation.

For decades, conservationists have struggled to accurately count the population of the Ganges River dolphin. "Their surfacing is too fast and too rare to rely on visual surveys," said Mohammad Abdul Aziz, a researcher from Jahangirnagar University.

The new system, developed by the Institute of Hydrobiology at the Chinese Academy of Sciences, shifts the focus from sight to sound. Originally designed to protect the Yangtze finless porpoise in China, the technology filters through river noise to identify the unique sonar pulses of the dolphins.

"With this technology, we are finally able to hear what we could not see," said Hao Yujiang, a professor at the institute.

Hao is working as part of a China-Bangladesh Belt and Road Initiative collaboration launched in January. Backed by the Alliance of International Science Organizations, the project aims to strengthen ecological research on Ganges River dolphins by applying conservation technologies developed along China's Yangtze River.

Threatened by habitat degradation, sand mining and fishing, the dolphin's numbers have continued to decline in recent years.

The Chinese system will enable experts to more accurately assess the regional dolphin population and take measures accordingly, such as producing reports that may influence government policy related to the environment and conservation.

Developed through years of conservation work on the Yangtze finless porpoise, the monitoring system automatically recognizes dolphin sonar signals in real time, filtering them from background noise. It can be fine-tuned using 26 adjustable parameters to adapt to different river conditions, Hao said.

During the Bangladeshi survey, Chinese acoustic engineer Chen Yuwei repeatedly adjusted the system based on the dolphins' activity patterns, refining recognition thresholds and reducing false alarms.

"The recognition rate turned out to be far higher than what we could achieve with visual monitoring alone," Chen said, pointing to pulsing waveforms on a laptop screen. "Many of the movements behind these signals are completely invisible to the human eye."

Over several days of crosschecking, the results were striking. Nearly every dolphin spotted by observers was also detected acoustically, while acoustic detection results were rarely accompanied by visual signals.

"That confirmed the irreplaceable role of sound-based monitoring for this species," said Hao.

To complement the underwater data, another Chinese researcher, Zhou Haojie, deployed drones to survey the river basin from above, mapping habitats and capturing rare footage of dolphins breaking the surface.

Zhou said the links between the Ganges and China's Yangtze are tangible.

The Ganges River dolphin and China's Baiji dolphin share similar evolutionary paths. Both have adapted to turbid rivers, with most of their vision lost, and relying on echolocation to survive. Both serve as ecological barometers for the health of their rivers.

When the survey concluded on Jan 9, the team had identified multiple key dolphin habitats, including high-density activity zones near downstream sandbars.

"This is not just technology transfer, it is a shared exploration," said researcher Aziz.

"The Chinese team not only brought equipment, but also an entirely different way and philosophy of conservation," he added.

Contact the writers at weiwangyu@chinadaily.com.cn