The dolphins retreated to parts of the river that once survived due to ferries that would carry passengers from Hong Kong and Macau, according to Reuters, marine scientist Lindsay Porter of the University of St. Andrews.
Porter said ferry traffic was suspended in March, allowing scientists to study how underwater noise affected their behavior.
Porter and his team drop the microphone from a boat and use the drone to use the dolphin. Their research suggests that dolphins adapt quickly to more tranquil environments and are now likely to bounce back into the river.
According to WWF Hong Kong, this type of dolphin was first recorded in local waters in the 1600s. The population at Pearl River Estuary is estimated to be around 2,500 individuals, but the organization says there has been a “worrying shortfall” in recent years.
“I sometimes feel that we are studying the slow demise of this population, which can be really sad,” Porter said according to Reuters.
WWF Hong Kong states that the dangers of these dolphins include over-watering, water pollution and heavy sea traffic and coastal development. However, research being conducted in this area could help bring the dolphin population elsewhere, Porter told Reuters.
CBS News has reached out to Porter at St. Andrews University for more information.