5:15 PM - 6:45 PM
[HTT16-P08] Development of a high-resolution trace element analysis for estimating the migration regions of Todarodes pacificus (Japanese flying squid)
Keywords:trace element, LA-ICPMS, Todarodes pacificus , carbonate, migration history
Todarodes pacificus is one of the major fisheries resources in Japan. However, catches have been a drastic decrease in recent years (Fisheries Agency, 2023). Therefore, it is necessary to elucidate the factors causing resource fluctuations through comparisons among ecological information, migration mechanisms, and environmental factors. Based on the field observations such as archival tag, T. pacificus is assumed to consist of two groups: one born in autumn that migrates from the Tsushima region to the Japan Sea, and another born in winter that mainly migrates from the East China Sea to the Pacific Ocean. Although resource management has been controlled separately under this assumption, the detailed migration patterns are not well understood individually. Since the statolith of T. pacificus is formed by the carbonate accretion with growth, its chemical composition records environmental and ecological information. The δ18O in carbonate is well known as a water temperature proxy (e.g., Grossman and Ku, 1986), thus it is possible to estimate the migration regions based on isothermal zones (e.g., Sakamoto et al., 2019). However, since the isothermal zones extend widely in the east-west direction, it is difficult to estimate the migration region in the east-west direction. On the other hand, there is a gradient in the east-west direction for trace element concentration. This implies that trace elements could be used as an identifying habitat proxy in the east-west direction. Therefore, it is expected that combining δ18O analysis with trace element analysis would enable high-spatial-resolution reconstruction of the migration histories of T. pacificus. However, targeted trace elements and their characteristics to identify habitats have not been established yet. Furthermore, it has been suggested that the autumn-born and winter-born groups may commute through the Tsugaru Strait. This implies that there is a possibility that some of T. pacificus caught in the Japan Sea may have originated in the Pacific Ocean, and vice versa. Therefore, it is necessary to use juvenile squid that is presumed to have grown in the Japan Sea or the Pacific Ocean in order to accurately evaluate the characteristics of the habitats for each area. In this study, we conducted trace element analysis (Mg, P, S, K, Ca, Mn, Sr, Ba) of small T. pacificus statolith caught in Odawara and Ishikawa using the LA-ICPMS (Raijin α + Agilent 8900) at Kyoto University. Our aim is to construct an environmental proxy for identifying migration areas.
Statolith of T. pacificus has a complex shape. The "wing" area connected to the nerve is expected to have a different trace element concentration from other parts due to its high organic content. To evaluate the influence of organic materials around the wing area, trace element maps were obtained. P and S contents are high in the wing area, while other parts show low contents. This suggests that the area near the wing may be affected by organic matter. Except for P and S, other elements show concentric distributions. This suggests that the same trace element pattern can be obtained regardless of the direction of analysis. Based on line analysis excluding the wing area, Mg and Mn contents decreased from the core to the margin regardless of the difference in the caught region. These elements are expected to be mainly contained in organic matter (Hussy et al., 2022), suggesting that they reflect biophysical influences during growth. Sr content patterns for each individual show variability, indicating that Sr content is affected by various factors. Therefore, Sr content is not suitable as an identifying habitat proxy. On the other hand, except for the statolith core, K and Ba contents in the statolith from the Japan Sea are higher than those from the Pacific Ocean. Furthermore, Sr/Ba ratio in the statolith from the Pacific Ocean is higher than that from the Japan Sea. Therefore, K, Ba, and Sr/Ba would be utilized as an identifying habitat proxy. To evaluate whether these elemental characteristics both in the Japan Sea and the Pacific Ocean are general, verification should be conducted using individuals caught at multiple sites. If common characteristics are confirmed in each region, it is expected that an identifying habitat proxy for T. pacificus will be established.
Statolith of T. pacificus has a complex shape. The "wing" area connected to the nerve is expected to have a different trace element concentration from other parts due to its high organic content. To evaluate the influence of organic materials around the wing area, trace element maps were obtained. P and S contents are high in the wing area, while other parts show low contents. This suggests that the area near the wing may be affected by organic matter. Except for P and S, other elements show concentric distributions. This suggests that the same trace element pattern can be obtained regardless of the direction of analysis. Based on line analysis excluding the wing area, Mg and Mn contents decreased from the core to the margin regardless of the difference in the caught region. These elements are expected to be mainly contained in organic matter (Hussy et al., 2022), suggesting that they reflect biophysical influences during growth. Sr content patterns for each individual show variability, indicating that Sr content is affected by various factors. Therefore, Sr content is not suitable as an identifying habitat proxy. On the other hand, except for the statolith core, K and Ba contents in the statolith from the Japan Sea are higher than those from the Pacific Ocean. Furthermore, Sr/Ba ratio in the statolith from the Pacific Ocean is higher than that from the Japan Sea. Therefore, K, Ba, and Sr/Ba would be utilized as an identifying habitat proxy. To evaluate whether these elemental characteristics both in the Japan Sea and the Pacific Ocean are general, verification should be conducted using individuals caught at multiple sites. If common characteristics are confirmed in each region, it is expected that an identifying habitat proxy for T. pacificus will be established.