An updated checklist of fishes of Dongsha Island, Taiwan, northern South China Sea
Abstract
Dongsha Island, situated in the northern part of the South China Sea, is surrounded by coral reefs and deep-sea habitats. The coastal areas of the atoll, a marine protected area, serve as important nursery habitats for many reef fish species. At the same time, the offshore deep-sea continental slopes are historically important fishing grounds. Although previous inventories primarily focused on coral reef fishes within the atoll listing 652 species from73 families, comprehensive surveys of fishes from deeper waters have been incomplete. In this study, the species composition of the fish fauna around Dongsha was updated by analyzing large volumes of frozen bycatch from commercial deep-sea trawlers operating in the area for the past four years and reviewing the existing literature. The species list increased to 1087 species belonging to 167 families, including several documented as new records and potentially undescribed species. This updated checklist also includes images of each species and most of their sagittal otoliths. This will assist further taxonomic work and significantly enhance understanding of marine biodiversity in the South China Sea.
Methodology and Implementation Steps
Our study used two distinct datasets: occurrence records from the literature on coral and seagrass-associated shallow-water fishes and newly collected occurrence data from deep-water fishes sampled via commercial bottom trawlers. Both datasets represent different ecological settings with distinct sampling techniques. For the former, we reviewed existing literatures and validated nomenclatures. From February to early July each year from 2021 to 2024, we obtained frozen samples from fishermen at Zhengbin fish port in Keelung, Taiwan that were collected from the commercial bottom trawlers operating in the waters off Dongsha Island at depths of approximately 300–600 meters (18°49'N to 20°45'N and 112°46'E to 116°15'E). These samples consisted mainly of fishes and other invertebrates and weighed approximately 30 kg each. The total samples (n = 198) processed collectively weighed more than 6,000 kg. We collected samples bi-monthly, carefully selecting specimens to ensure they represented the broadest possible diversity within the catch. These samples were then transferred to our lab and defrosted sequentially.
Each fish was measured for standard length (SL), total length (TL), and weight (WT), with preanal length (PAL) recorded when necessary. Specimens were photographed before muscle tissue was subsampled from the right caudal region. These tissue samples were preserved in 95% ethanol and deposited at the National Academy of Marine Research in Kaohsiung for future reference.
For images of teleostean otoliths, the left sagittal otoliths were primarily used; right otoliths were reversed for consistency and noted with an (R) in each caption. These otoliths were coated with a thin layer of gold using an ion sputter machine (MCM-100P, Sec, South Korea) to enhance the visibility of the sulcus. In addition, images of small-sized otoliths were captured using a scanning electron microscope (JSM-7100FLV, Jeol, Japan). Otoliths were archived at the Marine Paleontology Lab, Biodiversity Research Center, Academia Sinica, registered under the code CHLOL. Scientific names and taxonomic attributions adhere to the latest edition of the Catalog of Fishes. Our remarks provide information on species distribution and abundance estimates around Dongsha Island.
Innovation and Cross-Disciplinary Collaboration
The earliest record of the ichthyofauna around Dongsha Island was around 30 years ago, which was later incorporated by Randall and Lim (2000) into a comprehensive checklist of South China Sea fishes. Despite updates by Shao et al. (2008, 2011) in their checklists for southern Taiwan and the northern South China Sea, there has until now been no concerted effort to synthesize new data from subsequent studies. Our study presents the most exhaustive inventory to date, utilizing existing literature and newly sampled fish collections conducted between 2021 and 2024. More importantly, this is the first attempt to target samples derived from commercial fisheries, which operate with much higher fishing effort, generate larger catches using bigger fishing gear, and more broadly cover deeper and remote areas compared to typical scientific research vessels. Thus, our results provide novel insights and deeper knowledge of the fish fauna around Dongsha Island, especially for the less explored western waters off the atoll. Additionally, this study provides actual images and otoliths of the fishes from Dongsha Island, offering a tool for species identification, and as reference to other fields such as paleontology.
Expected Results and Contributions
In this study, we cataloged a total of 1087 species across 167 families, and our recent efforts alone identified 337 species from 93 families. Thirteen species have been described from 2021 to 2024 around Dongsha Island, and 89 species have been newly recorded in this study, with 35 species still undescribed and requiring further investigation. The updated checklist not only enriches our understanding of marine biodiversity but also serves as a critical resource for future research and conservation initiatives. Notably, based on the IUCN Red List of Threatened Species (IUCN 2012), there were two fish species recorded in Dongsha Island that were considered Critically Endangered; nine species are listed as Endangered; ten as Vulnerable; and six as Near Threatened. However, most species were categorized as Least Concern or Data Deficient, highlighting the need for continued research and conservation efforts to ensure sustainable fishing practices in the region.
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