Rare pink dolphins are returning to the waters between Hong Kong and Macau after the coronavirus pandemic halted ferries, but scientists remain deeply concerned about their long-term survival in one of the world's busiest sea lanes.

The tell-tale flash of pink leaping from the waters alerts Naomi Brennan to the presence of a local Chinese white dolphin and she jots the animal's location into a GPS device.

“Today we encountered three different groups of dolphins — six adults and two sub-adults,” she explained.

“They were engaging in a range of behaviour, from feeding to travelling and socialising.”