[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-17] Comparative study on environment experienced by jack mackerel in the East China Sea between 1960s and 2000s.

*Tomihiko Higuchi¹, Motomitsu Takahashi², Megumi Enomoto¹, Kotaro Shirai¹, Shin-ichi Ito¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Nagasaki, Japan)

Keywords:otolith isotope analysis, fish migration, temperature history

Jack mackerel Trachurus japonicus is distributed on the continental shelf waters along with the subtropical Kuroshio Current and the Tsushima Warm Current in the western North Pacific. The East China Sea (ECS) is one of the major spawning and nursery grounds for jack mackerel and understanding the recruitment processes of jack mackerel into the fishing grounds in the ECS is important. However, information on how jack mackerel respond to decadal temperature variability is limited. Also, it is known that jack mackerel change their habitat from the surface to the semi-demersal layer in early life stage in the ECS. This study aims to know the migration history including the vertical habitat layer change of jack mackerel in the ECS during the 1960s and the 2000s. To estimate their environment experienced during the larval and juvenile stages, oxygen (δ¹⁸O) stable isotope of jack mackerel otolith was analyzed by using isotope ratio mass spectrometer (n=422). Fish samples were taken at the ECS in 1960-70s and 2000-2010s (15 individuals, each period). The high-precision micro-milling system GEOMILL 326 was used for otolith subsampling. At every 10 daily rings (20-30 daily rings in section including core), a ring was tracked and used as the boundary of the micro-milling increment. As a result, there was no significant differences in temperature experienced by the larval-juvenile stages, which is estimated from δ¹⁸O, between the two survey periods. This indicate that both jack mackerel from different periods likely utilized a similar environment under a changing ocean state. By using assimilated ocean data (SODA2.2.4 for 1960s, 3.12.2 for 2000s), we estimated the distribution area of jack mackerel in each age. In the early life stage (~60 daily age), distribution areas were different between the periods and individuals in the 1960s migrated in the north compared with those in the 2000s. There was a significant positive relationship between habitat temperature and growth rates based on otolith increment width during the juvenile stage. This suggested that the effect of water temperature on the growth of jack mackerel in the early life stage. Thus, jack mackerel in ECS likely adapted to decadal climate variability and select the preferred environment.