Japan Geoscience Union Meeting 2016

Presentation information

Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-TT Technology & Techniques

[M-TT28] Frontiers in Geochemistry : Prospect for geochemistry and cosmochemistry in future

Sun. May 22, 2016 10:45 AM - 12:15 PM A04 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Hajime Obata(Marine inorganic chemistry division, Atmosphere and Ocean Research Institute, University of Tokyo), Hirochika Sumino(Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo), Tetsuya Yokoyama(Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology), Takafumi Hirata(Graduate School of Science, Kyoto University), Urumu Tsunogai(Graduate School of Environmental Studies, Nagoya University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Shogo Tachibana(Department of Natural History Scieces, Hokkaido University), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Gen Shimoda(Geological Survey of Japan, AIST), Hiroyuki Kagi(Geochemical Research Center, Graduate School of Science, University of Tokyo), Yusuke Yokoyama(Atmosphere and Ocean Research Institute, University of Tokyo), Chair:Hirochika Sumino(Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo), Tetsuya Yokoyama, Hajime Obata(Marine inorganic chemistry division, Atmosphere and Ocean Research Institute, University of Tokyo)

11:30 AM - 11:45 AM

[MTT28-10] Freshwater eel conservation and Geochemistry

*kenzo kaifu1, Kotaro Shirai2 (1.Chuo University, 2.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:eel, otolith, stable isotope

The Japanese eel, Anguilla japonica, have continued to decrease since the 1970’s and appear to have reached a historically critical situation in recent years. Finally, this commercially important species was listed as endangered in the IUCN Red List of Threatened Species. Serious decline of the Japanese eel population requires feasible countermeasures for conservation and sustainable use.
The Japanese eels have been intensively stocked by the national government and fisheries cooperatives for the purpose of stock enhancement in various areas of Japan. The primary method of this is to release small yellow eels from eel farms into rivers and lakes. This stocking practice has been conducted for more than 100 years without being validated its effectiveness to enhance eel stock, while fish stocking includes several kinds of risks such as disturbances of distribution range, disturbances of genetic structures, and spreading diseases and parasites. A method to discriminate naturally recruited wild eels from stocked ones is undoubtedly important, however, no technics had been developed to our knowledge.
Because Japanese eel is a panmictic fish species consisting of a single spawning population, wild and stocked individuals cannot be discriminated genetically. Geochemistry, however, has opened up a possibility to discriminate eels of different origins recently. Oxygen and carbon stable isotope ratios of otolith (calcium carbonate crystal in the fish inner ear) basically depends on the source of environmental water. According to quadratic discriminant analysis based on otolith oxygen and carbon stable isotope ratios, 98.6% of 420 Japanese eels (106 wild and 314 cultured eels) were successfully discriminated into wild and cultured individuals.
Same as the Japanese eels, 8 of 13 freshwater eel species assessed are categorized as threatened or near threatened in the IUCN Red List of Threatened Species. The discrimination method shown above can be applied on these species such as European eel that intensively stocked under Eel Management Plans. Through otolith stable isotope analysis, geochemistry sheds light upon depletion of freshwater eel populations.