Kōzushima Island is blessed with fine harbors, and the island's fishing industry prospered from ancient times. Bonito fishing prospered in the Seven Islands of Izu and in order to preserve the freshness of caught bonito fish, the fish were unloaded at Kōzushima Island and then processed to make dried bonito. Bonito fishing held such an importance that a sacred event known as "bonito catching"was held in a shrine on the island.