Anthropogenic impacts on the distribution of wild and cultured Japanese eels in the Tone River watershed, Japan, from otolith oxygen and carbon stable isotopic composition

  • Kohma AraiEmail author
  • Hikaru Itakura
  • Akihito Yoneta
  • Kenzo Kaifu
  • Kotaro Shirai
  • Yoichi Miyake
  • Shingo Kimura


Effective management decisions are vital for the declining Japanese eel Anguilla japonica. Elucidating the distribution range of wild eels (i.e., naturally recruited individuals) represents the first step in resource management, although stocking of cultured eels throughout the waters of Japan masks the original distribution range of wild eels. Herein, we applied a recently developed discrimination model based on otolith oxygen and carbon stable isotopic ratios (δ18O and δ13C) to determine the distribution range of wild eels throughout the Tone River watershed, which is the largest fisheries ground for this species. The model indicated that eels naturally recruit up to 200 km in the catchment area from the river mouth. Although natural recruitment was confirmed at all sampling sites, the percentages of wild eel occurrence at each site ranged from 56 to 100% of sampled individuals. The presence of wild individuals at sites above river-crossing structures indicates that some individuals successfully navigate through these structures. The operation of sluice gates and fish passes installed on artificial structures might facilitate the recruitment of individuals in areas above the structures and further upstream in the watershed. Difference in the percentages of wild eels among sampling sites might be a product of major variation in the abundance of cultured eels stocked at respective sampling sites and nearby areas.


Anguilla japonica Natural recruitment Stocking River-crossing structures Random forest classification 



We thank the Kasumigaura, Shimotsuga, Toumou, and the Karasugawa Fishery Cooperatives of the Tone River watershed for their cooperation with this study. We are also deeply grateful to IDEA Consultants, Inc. and S. Matsuzaki of the National Institute for Environmental Studies for kindly providing us otolith samples and eels. We acknowledge the Tone River mouth tidal barrage administration office and the Tone water transmission office of the Japan Water Agency and the Kasumigaura River administration office of the Ministry of Land, Infrastructure, Transport and Tourism, Kanto Regional Development Bureau of Japan for providing sluice gate operation data. We also thank T. Ishikawa of Tochigi Prefectural Government, T. Kimura of the Shimotsuga Fishery Cooperative, and the members of the Biological Oceanography Group, Atmosphere and Ocean Research Institute, The University of Tokyo for their help in the fieldwork. We are also grateful to N. Izumoto for performing isotopic measurements of otolith samples. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant no. JP16H04734 and was conducted as a commissioned project of the Ministry of the Environment, Japan. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.

Supplementary material

10641_2019_915_MOESM1_ESM.pptx (59 kb)
Supplementary Table 1 Individual data for eels collected in the Tone River watershed (PPTX 59 kb)


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Graduate School of Frontier SciencesThe University of TokyoChibaJapan
  2. 2.Atmosphere and Ocean Research InstituteThe University of TokyoChibaJapan
  3. 3.Graduate School of ScienceKobe UniversityKobeJapan
  4. 4.Faculty of LawChuo UniversityTokyoJapan

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