Indo-Pacific humpback dolphins: learn about the pink dolphins

We’ve all heard about humpback whales. They are probably the most famous baleen whale species. But did you know humpback dolphins existed? There are actually four different species of humpback dolphins, all grouped in the genus Sousa. This month, we cover Sousa chinensis, the Indo-Pacific humpback dolphin. This coastal dolphin needs our help; let’s find out more about it!

A pink dolphin

Indo-Pacific humpback dolphins can appear grey, white or pink: it depends mainly on their location. In fact, we can find mostly white dolphins in China, grey dolphins in the Indian Ocean, and some pink dolphins in Singapore, Thailand, and Hong Kong. Scientists do not fully know why some dolphins turn pink but some said it could be due to thermoregulation in the blood vessels close to the dolphins’ skin.

A coastal habitat means more human threats

These coastal dolphins face multiple human threats. Some of the most notable include bycatch, injuries, and entanglements in gillnets. Studies reported a high proportion of injuries in Taiwanese humpback dolphins for example, which were linked to fishing gear.

Huge development projects including new residential infrastructure, windmills, and industries can disturb the dolphins’ habitat in different ways. The noise from construction projects as well as noise from wind turbines can disturb the communication and feeding of the dolphins, especially since they use echolocation. In addition, the destruction of coastal habitats can reduce the amount of prey available to dolphins.

Finally, chemical pollution and microplastics are major threats to these dolphins’ recovery. Chemicals including flame retardants, pesticides, and heavy metals are toxic to dolphins and can harm their immune and reproductive systems, making it harder for populations to stay healthy. Some studies have reported a high occurrence of skin lesions of all sorts. They could be linked to a weak immune system.

Conservation status of Indo-Pacific humpback dolphins

The IUCN lists Indo-Pacific humpback dolphins as a vulnerable species because their population is decreasing; it is the result of the multiple threats these dolphins face. The population is also heavily fragmented which may prevent gene flows and successful recovery for the species.

In Hong Kong, the population is protected by the Wild Animals Protection Ordinance, Marine Park Ordinance, and the Environmental Impact Assessment Ordinance. In mainland Chinese waters, the species is a Protected Species of the First Order. Bangladesh is also currently establishing a Marine Protected Area to protect these dolphins from further harm.

However, the IUCN assessment states that while these countries have taken action to protect Indo-Pacific humpback dolphins, there is a clear lack of enforcement, management of the threats, and conservation research for the species. Countries should thus aim to tackle the threats to Indo-Pacific humpback dolphins, to allow them to recover.

The Taiwanese population is endangered

Less than 50 individuals live on the East Coast of Taiwan. Scientists who looked at the population’s genes reported that the Taiwanese dolphins are distinct from other Indo-Pacific humpback dolphins. It means that the members of this small population do not reproduce with their neighbors, which can reduce the chances for these dolphins to survive long term. NOAA declared the Taiwanese population endangered under the Endangered Species Act in 2018. Since then, Taiwan has created a marine sanctuary to try to protect these dolphins.

What can be done to protect these animals?

According to conservation scientists and local NGOs, based on the Taiwanese situation, here are the recommendations for immediate actions to protect Indo-Pacific humpback dolphins:

1. Establish a ban on gill and trammel nets in their habitats.
2. New coastal developments should be located away from their habitats.
3. Establish mandatory routes and speed limits for vessels to reduce both noise and the risk of vessel strikes
4. Reduce pollution (air, water, soil).
5. Increase natural river flows.
6. Establish regulations to limit human-caused underwater noise levels

Sources and further reading

• Zhu, J., Yu, X., Zhang, Q., Li, Y., Tan, S., Li, D., … & Wang, J. (2019). Cetaceans and microplastics: First report of microplastic ingestion by a coastal delphinid, Sousa chinensis. Science of The Total Environment, 659, 649-654.
• Chen, B., Gao, H., Jefferson, T. A., Lu, Y., Wang, L., Li, S., … & Yang, G. (2018). Survival rate and population size of Indo‐Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, China. Marine Mammal Science, 34(4), 1018-1033.
• Wang, J., Hung, S., Yang, S., Jefferson, T. & Secchi, E. (2008). Population differences in the pigmentation of Indo-Pacific humpback dolphins, Sousa chinensis, in Chinese waters. , 72(4), 302-308. https://doi.org/10.1515/MAMM.2008.030

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