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There's been a 30% rise in the number of pink dolphins seen in Hong Kong's Pearl River since March.

Since coronavirus there has been less water traffic such as boats and ferries being used.

This has made the surrounding waters a lot calmer and quieter which has encouraged the dolphins to come back.

The mammals - also known as Chinese white dolphins and pink dolphins - were moving back into parts of the Pearl River Delta that they would usually avoid because of the ferries that connect Hong Kong and Macau.

Scientists have been given a rare chance to study the pink dolphins and see how noise in the water affects them.

They used drones and small microphones to watch the dolphins and found that the population had grown since the area got quieter!

Marine scientist Lindsay Porter of the University of St. Andrews has been studying Hong Kong's dolphins for 30 years has said: "These waters, which were once one of the busiest thoroughfares in Hong Kong, have now become very quiet."

The research suggested that if the noise stayed away more pink dolphins would come to the Pearl River.

Scientists believe that there's about 2,000 pink dolphins in the Pearl River delta with a recent study showing 52 entering the water near Hong Kong.

There are efforts being made to stop the decline of dolphins in Hong Kong, there are three marine parks where shipping is limited but not banned and dolphins are found there but the Hong Kong WWF says the animals still need protecting from boats when they move between these areas.

Scientist Lindsay Porter says more needs to be done to protect them: "I sometimes feel that we're studying the slow demise of this population, which can be really sad."