Zoological Studies

Vol. 59, 2020

(update: 2020.04.22; 06.09)

Estimations of Riverine Distribution, Abundance, and Biomass of Anguillid Eels in Japan and Taiwan Using Environmental DNA Analysis

Hikaru Itakura1,2,*, Ryoshiro Wakiya3, Masayuki K. Sakata4, Hsiang-Yi Hsu5, Shih-Chong Chen5, Chih-Chao Yang5, Yi-Cheng Huang5, Yu-San Han5, Satoshi Yamamoto6, and Toshifumi Minamoto4


1Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, 146 Williams St., Solomons, MD 20688, USA. *Correspondence: Tel: +1-410-231-8037.E-mail: itakurahikaru@gmail.com (Itakura)
2Graduate School of Science, Kobe University, 1-1 Rokkoudaichou, Nadaku, Kobe, Hyogo 657-8501, Japan
3Research and Development Initiative, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. E-mail: ryoshiro.wakiya@gmail.com (Wakiya)
4Graduate School of Human Development and Environment, Kobe University, 3-11, Tsurukabuto, Nadaku, Kobe, Hyogo 657-8501, Japan. E-mail: masa2k_mskk1518@yahoo.co.jp (Sakata); minamoto@people.kobe-u.ac.jp (Minamoto)
5Institute of Fisheries Science, College of Life Science, National Taiwan University, No.1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan. E-mail: d03b45003@ntu.edu.tw (Hsu); f05b45011@ntu.edu.tw (Chen); chihchao1123@gmail.com (Yang); ethan831231@gmail.com (Huang); yshan@ntu.edu.tw (Han)
6Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan. E-mail: s_yamamoto@terra.zool.kyoto-u.ac.jp (Yamamoto)

(Received 31 December 2019 / Accepted 21 April 2020)
Communicated by Benny K.K. Chan

Although populations of anguillid eels have declined remarkably in recent decades, monitoring data on the spatial and temporal variation in their dynamics are often limited, particularly for tropical eel species. As there are often sympatries of multiple eel species in tropical rivers, identifying eel species based solely on morphological characteristics is challenging. Basin-scale surveys were conducted in rivers of southern Japan and northern Taiwan to investigate (1) whether the spatial distribution, abundance, and biomass of the tropical eel species, the giant mottled eel (Anguilla marmorata), can be monitored in rivers by comparing the results obtained from environmental DNA (eDNA) analysis with data from electrofishing and (2) the riverine distribution of the sympatric A. marmorata and the temperate eel species, the Japanese eel (Anguilla japonica), in this region using eDNA analysis. Although we found an much lower abundance of A. marmorata in the study region, we identified the eDNA of the species from all of the study sites (21 sites) where it was collected by electrofishing, in addition to 22 further study sites where it was not collected directly. This indicates that eDNA analysis has a greater sensitivity for detecting A. marmorata, making it a powerful tool for monitoring the spatial distribution of the species in rivers. We found a significant positive relationship between eDNA concentration and both the abundance and biomass of A. marmorata, and eDNA concentration seemed to better reflect the abundance of the species than did biomass. eDNA of both A. japonica and A. marmorata was identified from almost all rivers, indicating the sympatry of these species in this region, although the degree of sympatry differed between rivers. Though the eDNA concentration of A. japonica decreased significantly with increasing distance from the river mouth, no significant relationship was found for A. marmorata. This study is the first to demonstrate the potential usefulness of eDNA analysis for estimating the spatial distribution, abundance, and biomass of tropical eels in rivers and to further apply this method to investigate sympatry among anguillid species. eDNA analysis can help in obtaining data on the population dynamics of tropical eels, providing invaluable information for managing these species.

Key words: Anguilla japonica, Anguilla marmorata, Environmental DNA, Monitoring, Spatial distribution.

Citation: Itakura H, Wakiya R, Sakata MK, Hsu HY, Chen SC, Yang CC, Huang YC, Han YS, Yamamoto S, Minamoto T. 2020. Estimations of riverine distribution, abundance, and biomass of anguillid eels in Japan and Taiwan using environmental DNA analysis. Zool Stud 59:17. doi:10.6620/ZS.2020.59-17.

Supplementary Materials: Fig. S1 | Fig. S2