[A-OS12] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS12-P04] Development of a Method for Estimating the Experimental Environment of 0-year Pacific saury(Cololabis saira) using Otoliths and Eyeballs

*Takumi Ishimura¹, Daiki Kurosaki¹, Satoshi Suyama², Taiki Fuji², Toyoho Ishimura³, Nanako O. Ogawa⁴, Chisato Yoshikawa⁴, Yota Harada⁴, Naohiko Ohkouchi⁴, Shin-ichi Ito¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Japan Fisheries Research and Education Agency, 3.Kyoto University, 4.Japan Agency for Marine-Earth Science and Technology)

The Pacific saury (Cololabis saira) is widely distributed in sub-thermal to sub-arctic waters of the North Pacific and is one of the most important pelagic fish resources fished by Japan, Taiwan, Korea, and other countries. Although the life history of Pacific saury has been elucidated, the detailed migration route has remained unclear due to the lack of successful tagging and recapture surveys of Pacific saury. Another method to estimate the migration route is to use the oxygen stable isotope ratio in otoliths. In the method, the distribution area of the target fish is estimated as the range of seawater temperature and salinity corresponding to the oxygen stable isotope ratio of daily rings in their otoliths. However, since the contours of seawater temperature and salinity are distributed in an east-west direction, it is often difficult to specify the longitudinal position of their distribution based on the otolith oxygen isotope ratio, while the latitudinal distribution can be reasonably estimated. In this study, we focused on the nitrogen stable isotope ratio of the eye lens. The eye lens has a structure with multiple layers of membranes, and new membranes are formed as the lens grows. The eye lens is made from organic matter(protein) in which nitrogen and carbon are originated from a diet of fish. In addition, since the lens membrane is not metabolized after its formation, it retains the isotopic information of the environment at the time of its formation. It is expected that the combined use of independent indices, eye lens isotopes, and otolith oxygen stable isotopes increase the accuracy of estimation of the fish distribution area. In this study, we are aiming to develop a method for estimating the migration route and hence the empirical environment experienced by Pacific saury, using the combined method. Pacific saury from the field sampling was used, and otoliths and eye lenses were removed from the samples for analysis of oxygen stable isotope ratio in otoliths and nitrogen stable isotope ratio in the eye lens. Currently, we are conducting the analyses and the details will be shown at the session.