2023 Volume 27 Issue 2 Pages 15-24
It is widely known that sardine have population cycles, and that the peak of their populations comes approximately every 60 years for multiple sardine species in distant ocean regions in the world. Until present, although various environment factors, such as oceanographic and climate conditions, were studied to explain the population cycles of sardine resources, Earth’s outer liquid core has not been the subject of the study. The fluctuation of Earth’s outer liquid core is not able to be directly observed. Available data are those obtained indirectly through the ray of geomagnetism from the Earth’s outer liquid core. In this study, we used the geomagnetic data, and found out the followings: (i) a statistically significant correlation was identified between the Index of Geomagnetic Intensity (GEOM) and the Index of Sardine Scale Deposition Rate (SSDR: from 1840 to 2010) (R2=0.394, p=4.029E-20<0.001) and (ii) a statistically significant correlation was also identified between the Index of GEOM and the Sardine Catch Volume in Japan (SCV: from 1910 to 2010) (R2=0.243 (p=1.61E-07<0.001) .
Consequently, it can be argued that the fluctuation of geomagnetic intensity from Earth’s outer liquid core is one of the important factors that explain population cycles of sardine resources. Furthermore, we examined the variation of sardine resources back to 3000 years, 10,000 years and 800,000 years by using fluctuations of the geomagnetic intensity. As a result, in addition to the 60-year population cycle, we have found another population cycle that has population peaks in approximately every 300 years.
