[H-TT21] Development and applications of environmental traceability methods

[HTT21-P11] Tracing of the freshwater fish movement patterns and water dynamics by strontium stable isotope ratios and the elements concentrations analysis

*Konomi Fudamoto¹, Ki-Cheol Shin², Takanori Nakano², Seiichi Mori³, Manabu Kume⁴, Syotaro Nishida³, Ichiro Tayasu² (1.Graduate School of Science,Kyoto University, 2.Research Institute for Humanity and Nature, 3.Gifu-keizai University, 4.National Institute of Genetics)

Keywords:strontium stable isotope ratio, otolith, fish, water

In coastal area of Otsuchi, Iwate prefecture, spring water is abundant and thereby the rare freshwater three-spined stickleback (Gasterosteus aculeatus), which prefer cold water environment, inhabit here. This area was damaged by the tsunami caused by the 2011 off the Pacific coast of Tohoku Earthquake. During the reconstruction and recovery works, the understanding of the habitat range and the environmental conditions of the three-spined sticklebacks contributes to the appropriate ecosystem management. Strontium stable isotope ratio (⁸⁷Sr/⁸⁶Sr) has been used as a powerful indicator to trace the past movement patterns of fish because of the same ⁸⁷Sr/⁸⁶Sr value between fish and the water of its habitat. Therefore, we used ⁸⁷Sr/⁸⁶Sr indicator to elucidate the three-spined stickleback movement patterns.
First, we investigated the relationship between the ⁸⁷Sr/⁸⁶Sr of three-spined stickleback whole otoliths (ear bone) and the water in isolated water bodies. We confirmed that both water and fish have almost same ⁸⁷Sr/⁸⁶Sr.
Second, by analyzing the water of different rivers and tributaries in Otsuchi, we found that, just in one tributary of Kozuchi mainstream, ⁸⁷Sr/⁸⁶Sr and many element concentrations (e.g. Ca, Sr) were remarkably different between the upstream and downstream. Using ⁸⁷Sr/⁸⁶Sr and Sr concentration values of water, the downstream water was estimated to be mix of the upstream water, mainstream water and seawater (Contribution ratio; upstream: 82.6%, mainstream: 16.7%, seawater: 0.6%).
Then, using ⁸⁷Sr/⁸⁶Sr and elemental concentration of otoliths of fish captured in the upstream and downstream, we estimated their past movement patterns. We compared the water ⁸⁷Sr/⁸⁶Sr between the upstream and the downstream and the ⁸⁷Sr/⁸⁶Sr of otolith. As a result, it was possible to identify that stickleback lived in either upstream or downstream within single tributary; three-spined sticklebacks captured in the upstream (40 individuals in total) were not likely to move from downstream, while the fish caught at downstream (13 individuals in total) were estimated to have moved from the upstream or the mainstream. Furthermore, in the downstream, some fish otoliths showed a larger value of Sr/Ca than the others, which means that those fishes lived in high salinity environment in the past suggesting that the downstream population of three-spined stickleback was able to live in both fresh and brackish water environments.