In the normally busy water between Hong Kong and Macau, researchers have been delighted to discover a resurgence in rare, pink dolphins.

Within weeks of the high speed ferry links being shut down by the Coronavirus crisis, the marine mammals have made a massive comeback, with numbers rising by a third.

The local population of Indo-Pacific humpback dolphins are known as 'pink dolphins' for their distinctive colour. While other humpback dolphins exhibit white and marbled colouring, it is the population around the south Chinese coast that are noticeably pink.

However, the high volume of high-speed ferries linking the two Chinese SARs has made their sightings a rare event.

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The Macau-Hong Kong bridge was completed in 2018, but researchers say it is underused. Photo / Unsplash, Vicky T
The Macau-Hong Kong bridge was completed in 2018, but researchers say it is underused. Photo / Unsplash, Vicky T

After building began on the Macau-Hong Kong suspension bridge, sightings of the dolphins became so rare some worried they might have been driven to extinction.

But it was all a matter of busy traffic driving out the marine mammals.

Hong Kong's high-speed ferries cruise at 45 knots. Photo / Flickr.com, MV Horta
Hong Kong's high-speed ferries cruise at 45 knots. Photo / Flickr.com, MV Horta

Talking to the Guardian, marine biologist Dr Lindsay Porter of St Andrews University said their return was almost immediate.

"It was the last week in February, literally the week after the ferries stopped travelling between Hong Kong and Macau," she said. "I've been studying these dolphins since 1993 and I've never seen anything like this dramatic change before, and the only thing that changed is 200 ferries stopped travelling before," she said.

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Using a borrowed yacht from Hong Kong the research team were able to conduct a study in the empty ferry lanes.

Sure enough, there they were frolicking around. The animals were seen exhibiting normal dolphin behaviours, said Dr Porter: "socialising, splashing around on the surface, quite a bit of foreplay, quite a bit of sex."

Pink Dolphins are a rare sight in southeast Asia. Photo / 123rf
Pink Dolphins are a rare sight in southeast Asia. Photo / 123rf

Most of these activities are disrupted by maritime traffic, which can drive the dolphins to the edges of human populations.

The researchers who have partnered with WWF aim to return to measure the effect on the dolphins when ferries resume and have installed listening stations.
Macau's casinos draw 36 million visitors a year. Many of whom arrive via the high-speed ferry link from Hong Kong.

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These high-speed hydroplane ferries normally cruise at 45 knots (84 kmph) across the busy shipping channel, until the links were closed on 4 February until further notice.