10:00 AM - 10:15 AM
[ACG43-05] Northerly deviation of the first peak of the Kuroshio Extension during the Kuroshio Large Meander and changes in the position of Pacific saury fishing grounds
★Invited Papers
Keywords:Kuroshio Extension, Pacific saury, Kuroshio Large Meander, AI, ocean numerical model
Investigating the northern limit (NL) of the first peak of the Kuroshio Extension (FPKE) before (January 2015 to July 2017) and after (August 2017 to November 2022) the occurrence of the Kuroshio Large Meander (KLM) in August 2017, we show that the FPKE moved northerly several degrees comparing after and before the occurrence of KLM. Furthermore, since 2019, the NL has been trending northward year by year. The NL in 2019 was around 36.5 degrees north latitude, but in November 2022 it was around 38.5 degrees north latitude. Kawai (1989, Bull. Jpn. Soc. Fish. Oceanogr.) investigated the NL of the FPKE from 1933 to 1989 using ocean observation data and found that the interannual variability was remarkable. Then, he suggested that KLM is a factor of remarkable northward deviation reaching 39 degrees north latitude. Sugimoto and Hanawa (2012, J Oceanogr.) investigated the relationship between the path of the Kuroshio and the Kuroshio Extension from January 1993 to December 2008 using satellite sea level altimeter observations and found that the FPKE during KLM period is deviated to the north by about 1 degree on average compared to the nearshore non-large-meander periods. These past findings are consistent with this research.
The catch of Pacific saury in 2022 was the lowest ever at 17,910 tons, according to the Japan Fisheries cooperative of stick-held dip nets for Pacific saury. The catch began a downward trend in 2010, especially, has continued to decline since 2019, when it fell below 50,000 tons for the first time. The decline in Pacific saury catches is due to various factors, such as a decrease in resources by fishing pressure and changes in ocean conditions, and cannot be simply explained. But one of the factors is thought to be that the Pacific saury became difficult to move south along the coast of Japan due to the weakening Oyashio first branch (Watanabe, scheduled to be published in JAFIC technical review).
In recent years, the anomalous warm sea surface water temperature named as marine heatwave (MHW), near Japan, which is thought to be a factor in the weakening Oyashio first branch, has attracted attention. Various factors are thought to cause MHW, including meteorological phenomena and warm water eddies (Miyama et al. 2021, Front. Mar. Sci., Kuroda and Setou 2021, Remote Sens.). However, the discussion of the effects of the Kuroshio Current, which is an important heat source along the coast of Japan, seems insufficient.
In this study, we plan to present changes in the position of Pacific saury fishing grounds based on the relationship between changes of the Kuroshio path and changes of the NL of FPKE. In addition, we will introduce the Pacific saury fishing grounds AI prediction using the ocean numerical model constructed by Japan Fisheries Information Service Center (JAFIC), which was started in 2022 (Yabuki 2022, JAFIC Technical Review).
The catch of Pacific saury in 2022 was the lowest ever at 17,910 tons, according to the Japan Fisheries cooperative of stick-held dip nets for Pacific saury. The catch began a downward trend in 2010, especially, has continued to decline since 2019, when it fell below 50,000 tons for the first time. The decline in Pacific saury catches is due to various factors, such as a decrease in resources by fishing pressure and changes in ocean conditions, and cannot be simply explained. But one of the factors is thought to be that the Pacific saury became difficult to move south along the coast of Japan due to the weakening Oyashio first branch (Watanabe, scheduled to be published in JAFIC technical review).
In recent years, the anomalous warm sea surface water temperature named as marine heatwave (MHW), near Japan, which is thought to be a factor in the weakening Oyashio first branch, has attracted attention. Various factors are thought to cause MHW, including meteorological phenomena and warm water eddies (Miyama et al. 2021, Front. Mar. Sci., Kuroda and Setou 2021, Remote Sens.). However, the discussion of the effects of the Kuroshio Current, which is an important heat source along the coast of Japan, seems insufficient.
In this study, we plan to present changes in the position of Pacific saury fishing grounds based on the relationship between changes of the Kuroshio path and changes of the NL of FPKE. In addition, we will introduce the Pacific saury fishing grounds AI prediction using the ocean numerical model constructed by Japan Fisheries Information Service Center (JAFIC), which was started in 2022 (Yabuki 2022, JAFIC Technical Review).