【明報專訊】What are they?

You may not know what Indo-Pacific humpback dolphins are — however, its other name, Chinese white dolphins(中華白海豚), will certainly ring a bell. Whilst living in the coastal waters in the Indian Ocean and western Pacific Ocean, some populations can be found in the western part of Hong Kong.

Indo-Pacific humpback dolphins came into existence a long time ago in Hong Kong waters, even before your grandparents were born! Because of their unique appearance and agility characteristic, they attract people's attention and have become the underwater symbol of Hong Kong.

◆Are they really white?

Baby dolphins are called calves (singular: calf). The calves of Indo-Pacific humpback dolphins look very different from their parents. Newly born calves are grey. As they grow up, their colour gradually changes to white, leaving grey spots behind. Because of the blood vessels (血管) beneath their skin, the adults may seem to be light pink.

◆Why can the dolphins live in muddy waters?

The humpback dolphins can live in estuarine (河口) waters where the visibility (能見度) can be quite low. How do they "see" then? Similar to other dolphins and whales, they have a special skill called “echolocation” (回聲定位). They send out high-frequency (高頻率) sound waves (聲波), which will be reflected when hitting obstacles. By receiving and analysing the echo, the dolphins can locate objects and learn about their surroundings.

◆What threats are dolphins facing?

The humpback dolphins are facing a lot of challenges in Hong Kong such as marine pollution, heavy marine traffic and construction of infrastructure. The Cetacean Stranding Response Team (鯨豚擱淺行動組) is a collaborative project between Ocean Park Conservation Foundation, Hong Kong (OPCFHK) and Agriculture, Fisheries and Conservation Department (AFCD, 漁農自然護理署). Having dealt with over 350 stranding cases since 2006, the team concluded three major causes of death: entanglement in fishing nets, impacts by boats and infection with bacteria or parasites (寄生蟲).

text and photos: Ocean Park Hong Kong

◆How can we save the dolphins?

- If you come across stranded, injured or dead dolphins, please call 1823 to report the case to the AFCD.

- Reduce waste by not using disposable plastic products.

- Always bring your own bottle, bag, utensils and food containers.

■Glossary

agility (n) 敏捷

obstacle (n) 障礙物

infrastructure (n) 基礎建設

entanglement (n) 纏繞

[Smarties' Power English 第200期]