Is Japanese Folklore Concerning Deep-Sea Fish Appearance a Real Precursor of Earthquakes?

In Japan, folklore says that uncommon appearances of deep-sea fish are an earthquake precursor. If this folklore is proved to be true, the appearance of deep-sea fish could be useful information for disaster mitigation. However, a statistical survey has not been conducted on this subject because a database of such information had yet to be compiled. In Japanese domestic local newspapers, such appearances have often been reported because rare appearances might attract readers. The authors constructed a database of reports from newspapers, academic articles, and the marine museum. In this study, fish species generally implicated in earthquakes, such as oar-fish and slender ribbonfish, were the focus. Although the catalog used might not include all of the events of deep-sea fish appearances around Japan because of a lack of whole coverage observation, the earthquake occurrence rate after deep-sea fish appearances can be evaluated. Thus, the usefulness of the deep-sea fish appearance information for disaster mitigation was evaluated. From this investigation, the spatio-temporal relationship between deep-sea fish appearances and earthquakes was hardly found. Hence, this Japanese folklore is deemed to be a superstition attributed to the illusory correlation between the two events.