Distribution, abundance and conservation status of the eastern Taiwan Strait population of Indo-Pacific humpback dolphins, Sousa chinensis

Abstract

In 2002, a small population of Indo-Pacific humpback dolphins, Sousa chinensis, was discovered in the coastal waters of the eastern Taiwan Strait. Serious conservation concerns about this population led to a survey of most of the coastal waters of western Taiwan to better understand the status of this population. Surveys were conducted from boats (inshore waters) and a sea-kayak or land-based platforms (littoral waters inshore of large sandbars). Humpback dolphins were sighted 35 times, all within a stretch of inshore waters approximately 100 km (linear distance) and within 2 km from shore (none were observed in littoral waters). Including consideration of other records of this species, the main distribution of these dolphins was estimated to be approximately 515 km² of water off central western Taiwan, where industrialization is a serious and rapidly increasing issue. The population's abundance and density were estimated to be 99 individuals (coefficient of variation 51.6%) and 19.3 individuals/100 km², respectively, which is quite low when compared to the Pearl River estuary population. Assessing this population using the IUCN Red List criteria resulted in a “Critically Endangered” categorization, reinforcing the urgency of the situation.