The Indo-Pacific humpbacked dolphins are a sea treasure in crisis

Are you familiar with the Indo-Pacific humpbacked dolphin (Sousa Chinensis)?

They are unique residents in many parts of the world, sometimes called the Chinese White Dolphin, and those in the Asia-Pacific region are easily recognised by their iconic pinkish appearance.

Given their colouration, it’s little wonder that these dolphins are one of the most popular marine animals on the planet. But what do you know about this beautiful creature and how it is closely related to us?

About the Indo-Pacific humpbacked dolphin

It's obvious why these humpbacked dolphins are popular — they have pink skin and they look cute, and are common inhabitants of the tropical and temperate coastal waters of the western Pacific and eastern Indian oceans.

They have also been occasionally found in freshwater regions such as the Yangtze River, Min River, Jiulong River and Pearl River in China. Their skin colour may vary depending on the region and population.

Known to be friendly creatures, they get along well with humans, with about 2,500 Indo-Pacific humpbacked dolphins living in the waters of Hong Kong and the Pearl River Delta.

According to a report published by the Agriculture Fisheries and Conservation Department of Hong Kong, the number of Indo-Pacific humpbacked dolphins detected in Hong Kong waters between April 2019 and March 2020 rose from 32 to 52. However, their overall number has plummeted in the past decade, and this is a matter of concern.

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Fun dolphin facts

Blushing dolphins?

Indo-Pacific humpbacked dolphin are not born with their unique pink colour. Dolphin infants are dark grey, but as they mature, the grey colour fades and turns into their unique pink. Some scholars believe this is a kind of reaction to heat, just as human cheeks will turn red when we blush. It turns out that dolphins can be shy as well!

Expert hunters of the sea

Dolphins in general have a very high IQ, and this includes the Indo-Pacific humpbacked dolphins.

With 20 types of fishes on their favourites list, these dolphins have become adept at using tricks to catch prey. For example, they like to follow fishing boats to catch fish that have slipped through the nets, earning them a reputation as “free riders”.

The sea treasure of Hong Kong

The Indo-Pacific humpbacked dolphin is closely related to the past and present of Hong Kong.

In 1997, when Great Britain handed the sovereignty of Hong Kong back to China, the Indo-Pacific humpbacked dolphins were selected as the handover mascot.

If pandas are the national treasures of China, then the Indo-Pacific humpbacked dolphins can be considered the national treasure of Hong Kong.

"Mazu's Fish"

Besides Hong Kong, Taiwan also shares a tight bond with the Indo-Pacific humpbacked dolphins.

Taiwanese fishermen call them "Mazu's Fish" because these dolphins are more often seen in nearby waters during the third lunar month, which is also the time when the sea goddess and deity Mazu celebrates her birthday.

There is also a legend about a fishing boat that got into trouble when out at sea, but followed a humpbacked dolphin to safety. These dolphins have a reputation in many places indeed!

Marine animals with long lives

Scientists who study dolphins check the ages of Indo-Pacific humpbacked dolphins by analysing their teeth.

They discovered that these dolphins can live up to 40 years, which is a relatively long life for most animals.

The Indo-Pacific humpbacked dolphins that appear in the waters of Hong Kong, however, only have a life span of about 30 years.

Gather only in groups of four?

Due to Covid-19 regulations, only four people are currently allowed at public gatherings in Hong Kong, but it’s something the dolphins have been doing for a long time.

Indo-Pacific humpbacked dolphin are social animals that usually live in groups of three or four. Young dolphins acquire the necessary social skills by living with older dolphins, and these groups will travel around the world together.

Dolphins in crisis

Humans may not be able to hear the sounds that dolphins make, but that doesn't mean we can ignore their cries. What exactly are some of the threats the rare Indo-Pacific humpbacked dolphins face?

Extensive reclamation projects along the coast

Indo-Pacific humpbacked dolphins hunt prey in shallow waters no deeper than 10m.

With the rapid development of the Pearl River Delta, huge projects like the Hong Kong-Zhuhai-Macao Bridge and three-runway system for Hong Kong Airport have severely damaged the dolphins' habitat in and around Hong Kong.

The dolphins were forced to migrate to farther places in search of more living space, which has left an irreversible impact on the reproduction, growth, feeding and migration of the species.

For five consecutive years, there have been no sightings of these dolphins in the waters of the north-eastern Lantau Island (around the Hong Kong-Zhuhai-Macao Bridge and the airport).

Water pollution

Hong Kong has had severe water pollution in the past few years.

Frequent sea projects and dredging can easily block the gills of fishes and reduce the concentration of dissolved oxygen in the water. When fish growth slows, the Indo-Pacific humpbacked dolphins find it more difficult to feed.

Additionally, pollutants in the ocean such as organochlorine and heavy metals will accumulate in a dolphin's body and can seriously affect its health.

Sound pollution in the sea

Dolphins are very dependent on sounds, making use of sonar to measure distance, hunt, communicate and locate.

They make noises to echolocate the positions of companions, fishes and other objects, but the high-pitched noises produced by pile-driving hammers at the bottom of the sea as well as ships travelling on the water’s surface have made it difficult for dolphins to communicate with one another.

These sounds distract and confused the dolphins, and could result in severe injury.

Overfishing

Hong Kong does not place any restrictions on fishing.

In recent years, the number of fish caught in Hong Kong has greatly decreased, while the size and age of fish caught has changed from large and mature ones to smaller and younger ones.

Trawling has also damaged the sea bed. As fish numbers drop, the dolphin’s food supply also decreases.

Accidental collision with ships

Hong Kong's sea area is shrinking due to reclamation projects, yet maritime traffic has become increasingly heavy.

The high-speed passenger ships travelling between Hong Kong and Macao have disturbed the Indo-Pacific humpbacked dolphins living near the Pearl River Estuary, posing a threat to their safety.

For those who chance upon a humpbacked dolphin these days, t's not uncommon to see ones with scars from cuts by boat or ship propellers.