New paper provides evidence that critically endangered Taiwanese white dolphin is distinct, endemic subspecies

It was already clear that the pink-coloured dolphins living off Taiwan’s west coast were different from other nearby populations of the same species (Sousa chinensis, also known as the Indo-Pacific humpback dolphin). But a new paper has now revealed that the Taiwanese population also meets the criteria for being recognised as a subspecies.

The authors, John Wang, Shih Chu Yang and Samuel Hung*, who have been researching the critically endangered Taiwanese dolphins since 2002, propose a new scientific name for them - Sousa chinensis taiwanensis, to recognise their special local status.

The findings are the result of a study that compared pigmentation patterns in the Taiwanese population with those of neighbouring populations in the Jiulong River Estuary and the Pearl River Estuary, in the coastal waters of China. Dolphins in all three populations are born grey and gradually become pink or white with age, with the grey pigmentation becoming spots, and sometimes fading away altogether. However, examination of the spotting on individuals shows that the patterns on dolphins from the Taiwanese population are distinct from those in the other two regions.

In such situations, if at least 75% of the population is distinct from more than 99% of other provisional populations, it is commonly accepted as a subspecies. The study found that 94% of the Taiwanese population could be seen to be different from more than 99% of the other two populations, easily meeting this criterion. Further evidence of their uniqueness includes behavioural differences between the Taiwanese dolphins and other populations, and the fact that they are geographically isolated by the deep waters in the middle of the Taiwan Strait; Sousa chinensis are usually only found in shallow, coastal waters.

Recognition as a subspecies would make protective action for the Taiwanese dolphins even more urgent than previously thought, because their extinction would mean not only that Taiwan would lose this charismatic and ecologically important creature from its waters, but also that the world would lose a kind of dolphin that exists nowhere else. This subspecies may even be on a path to becoming a distinct species if the separation is sufficiently long to allow greater differentiation.

Local non-governmental organisations continue to call for official government recognition of the dolphins’ habitat, and for long-delayed action to reduce the five key threats to their survival – bycatch in fishing equipment, air and water pollution, noise and disturbance, loss of freshwater flow into their habitat, and land reclamation. Little has been done to address these threats over the thirteen years that researchers and concerned local groups have been drawing attention to them, and they continue on a trajectory towards extinction.

The full scientific paper about the subspecies recognition can be accessed freely (without subscription) at the website of the journal Zoological Studies at http://www.zoologicalstudies.com/content/54/1/36.

*While Hung has contributed to research on the Taiwanese population, he has also spent many years researching the Pearl River Estuary population from his base in Hong Kong.