Survey for Cartilaginous Fishes around Dongsha Island

Project Duration	2013-12-31 ~ 2014-12-30
Research Title	Survey of Chondrichthyan Resources in the Waters Surrounding Dongsha Island
Contracted Organization	NCKU Research and Development Foundation
Principal Investigator	Wang Chien-Ping
Co-Principal Investigator	Chen Yu-Yun
Project Participants	Fang Pei-Wen, Gan Hsiu-Ying, Wu Pei-Ying, Lin Hung-Tu, Chang Ching-Huang, Tseng Teng-Yu, Chi Hsin, Chien Yu-Chun
Keywords	Dongsha Island, sicklefin lemon shark, chondrichthyans
Abstract	Dongsha Atoll is located in the northern South China Sea and consists of Dongsha Island and the surrounding reef platform. Covering approximately 500 km², the atoll encompasses diverse habitats, including islands, coastal forests, lagoons, intertidal zones, coral reefs, and seagrass beds. Influenced by multiple ocean currents, the area forms productive fishing grounds that support diverse fish assemblages, including migratory, economically important, and predatory chondrichthyan species. Through capture, tagging, and release surveys, chondrichthyans were recorded in the inner lagoon, the western lagoon mouth, and the northern and southern waters. Population estimation indicated that the sicklefin lemon shark population numbered approximately 190 ± 38 individuals (mean = 189.5, SE = 37.5). Globally, the average haplotype diversity of lemon sharks is 0.28. Reanalysis of the Dongsha population revealed a haplotype diversity of 0.656, exceeding the global average and indicating higher genetic diversity. The global average nucleotide diversity (π) is 0.00056. Previous studies reported a value of 0 for Taiwanese lemon sharks; however, the current study found a value of 0.00139, also higher than the global average. These results suggest that the Dongsha sicklefin lemon shark population possesses exceptionally high genetic diversity. Historical demographic analysis showed a multimodal distribution, indicating a stable population without evidence of recent expansion. This suggests that the sicklefin lemon shark exhibits short-distance coastal migration and may have evolved into a relatively independent population. Although seven acoustic transmitters were deployed on chondrichthyans and three receivers installed in the inner lagoon, lagoon mouth, and northern island waters, the number of transmitters and receivers remains insufficient to fully understand migratory patterns. Continued tagging and expanded receiver deployment across the entire atoll are recommended to better understand distribution and behavioral ecology. Compared to marine teleosts, which have high fecundity and short generation times that facilitate rapid recovery of genetic diversity, chondrichthyans produce fewer offspring and have longer generation times. As a result, recovery of genetic diversity after population decline requires much longer periods, making conservation more challenging and urgent. Several chondrichthyan species recorded around Dongsha Island—such as the sicklefin lemon shark, blacktip reef shark, Himantura walga, and Aetobatus narinari—are globally recognized conservation species. Given the rich marine resources of the surrounding waters, further biological research is warranted, and the area holds strong potential as a model marine ecological conservation zone in Taiwan.