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Vol. 54, 2015
Diagnosability and
description of a new subspecies of Indo-Pacific humpback dolphin, Sousa chinensis (Osbeck, 1765), from the
Taiwan Strait
John
Y Wang1,2,3*, Shih Chu Yang4 and Samuel K Hung5
1CetAsia
Research Group, Thornhill, Ontario L4J-7X1, Canada
2Department of Biology, Trent University,
Peterborough, Ontario K9J-7B8, Canada
3National Museum of Marine Biology and Aquarium,
Pingtung 944, Taiwan
4FormosaCetus Company Ltd, Hualien 970, Taiwan
5Hong Kong Cetacean Research Project, Lam Tin,
Kowloon, Hong Kong, China
Abstract
Background: Subspecies recognition can affect
how people (scientists and non-scientists alike) view organisms and
thus has important implications for research on, as well as the
conservation of, these entities. Recently, a small group of
Indo-Pacific humpback dolphins was discovered inhabiting the waters off
central western Taiwan. This geographically isolated population
possesses pigmentation patterns that are subtly, but noticeably,
different from their nearest conspecifics in the neighbouring waters of
the Jiulong River Estuary and Pearl River Estuary of mainland China.
Due to this population’s low and declining numbers and the numerous
threats it faces, it was assessed as critically endangered by the Red
List of Threatened Species of the International Union for Conservation
of Nature. The purpose of this study is to examine the degree of
differentiation of the Taiwanese population to determine if subspecies
recognition is warranted.
Results: Analysis of the degree of differentiation
in pigmentation patterns revealed nearly non-overlapping distributions
between dolphins from Taiwanese waters and those from the Jiulong River
+ Pearl River estuaries of mainland China (the nearest known
populations). The Taiwanese dolphins were clearly diagnosable from
those of the Jiulong River + Pearl River estuaries under the most
commonly accepted ‘75% rule’ for subspecies delimitation (with 94% of
one group being separable from 99+% of the other). Evidence of
geographical isolation and behavioural differences also provided
additional support for the distinctiveness of the Taiwanese dolphins.
Conclusions: Together, the evidence
strongly demonstrated that the Taiwanese humpback dolphin population is
differentiated at the subspecies level and on an evolutionary
trajectory that is independent from that of dolphins from adjacent
waters of mainland China (i.e. Jiulong River + Pearl River estuaries).
As a result, the taxonomy of Sousa chinensis was revised to include two
subspecies: the Taiwanese humpback dolphin, Sousa chinensis taiwanensis subsp.
nov., and the Chinese humpback dolphin, Sousa chinensis chinensis (the
nominotypical subspecies). These subspecies are described, and the
holotype and paratype specimens for S.
c. taiwanensis are established.
Key words: Indo-Pacific; Taiwanese; Humpback
dolphin; New subspecies; Sousa
chinensis taiwanensis; Diagnosability; ‘75% rule’.
*Correspondence: E-mail: pdellape@fcnym.unlp.edu.ar
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