[A-OS15] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS15-P07] Evaluation of the Asymmetric distribution of Japanese eel recruitment to eastern and western Japan

*Yu-Lin Eda Chang¹, Mari Kuroki² (1.Application Laboratory, Japan Agency for Marine-Earth Science and Technology, 2.The University of Tokyo)

Keywords:Japanese eel, northern limit, recruitment

The cause of the asymmetric distribution of Japanese eel recruitment to the Pacific-eastern and Sea of Japan-western and coasts of Japan was examined using a composite analysis based on a 30-year simulation with a three-dimensional particle-tracking ocean circulation model. Virtual larvae (v-larvae) were released northeast of Taiwan over 240 days in three experiments that were conducted to evaluate the effect of ocean currents, salinity orientation, and diel vertical migration (DVM). V-larvae with salinity orientation and regular DVM accurately reproduced the asymmetric recruitment to eastern and western Japan, in which the northernmost recruitment on the eastern and western coasts of Japan was at southern Hokkaido (43°N) and near the Noto Peninsula (~37°N), respectively. V-larvae without salinity orientation failed to recruit to the western coast of Japan, and the experiment using near-surface DVM did not reproduce the observed asymmetric recruitment. The relatively southern location of the northernmost recruitment termination along the western coast of Japan was caused by southward currents in the subsurface layer of ~300 m depths near the Noto Peninsula that impeded v-larvae from moving northward. The use of a deeper diving depth during the daytime to avoid predators resulted in encountering southward current. V-larvae transport into the Sea of Japan (<30%) was less than into the western Pacific (>70%), and the recruitment duration took more than a month longer to reach the same latitude in the Sea of Japan compared to the western Pacific. The Tsushima Warm Current that entered the Sea of Japan was weak in comparison to the Kuroshio that flowed along the southeastern coast of Japan, and this was responsible for the differences in amount of recruitment and transport duration between the east and west sides of Japan. Other biological strategies, such as the timing of recruitment after metamorphosis may also contribute to the asymmetric recruitment in the real ocean.