11:00 〜 13:00
[AOS12-P02] Has the habitat of jack mackerel in the East China Sea changed? -Comparison between 1960s and 2000s-
キーワード：耳石、同位体分析、魚類回遊
Jack mackerel Trachurus japonicus is one of important fishery stocks in Japan. 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. It is known that they distributed on the continental shelf waters along with the subtropical Kuroshio Current and the Tsushima Warm Current in the western North Pacific. Also, it was estimated that jack mackerel change their habitat from the surface to the semi-demersal layer from about 30-60 daily age in the ECS. However, information on how jack mackerel respond to recent global warming is still insufficient. This study aims to know the migration history including the vertical habitat layer shift 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=539). Fish samples were taken at the ECS in 1960-70s and 2000-2010s (15 and 24 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 a significant positive relationship between habitat temperature and growth rates based on otolith increment width during only the juvenile stage. This suggested that the effect of water temperature on the growth of jack mackerel in the early life stage. However, there is no significant these relationship after 60 days age. Thus, the growth of jack mackerel depends on not only temperature but also other environment such as prey after habitat layer shift.
On the other hand, there was no significant differences in temperature experienced by the larval-juvenile stages, which is estimated from δ18O, between the two survey periods. After clustering analysis, individuals were separated six clusters. Most of clusters were structured by individuals of both 1960s and 2000s. This indicate that both jack mackerel from different periods likely utilized a similar environment under a changing ocean state. Thus, jack mackerel in ECS likely adapted to decadal climate variability and select the preferred environment.
As a result, there was a significant positive relationship between habitat temperature and growth rates based on otolith increment width during only the juvenile stage. This suggested that the effect of water temperature on the growth of jack mackerel in the early life stage. However, there is no significant these relationship after 60 days age. Thus, the growth of jack mackerel depends on not only temperature but also other environment such as prey after habitat layer shift.
On the other hand, there was no significant differences in temperature experienced by the larval-juvenile stages, which is estimated from δ18O, between the two survey periods. After clustering analysis, individuals were separated six clusters. Most of clusters were structured by individuals of both 1960s and 2000s. This indicate that both jack mackerel from different periods likely utilized a similar environment under a changing ocean state. Thus, jack mackerel in ECS likely adapted to decadal climate variability and select the preferred environment.