Photo/IllutrationThe left background of this photo taken on Sept. 1 from the coast of Sarufutsu, Hokkaido, used to feature the islet of Esanbehanakitakojima. (Provided by Hiroshi Shimizu)

  • Photo/Illustraion
  • Photo/Illustraion

An islet off Hokkaido that is used to delineate Japan’s territorial waters has disappeared, prompting the Japan Coast Guard to plan a search mission in the northern sea area.

The uninhabited islet, named Esanbehanakitakojima, is supposed to be located about 500 meters off the coast of Sarufutsu village near the northern tip of Hokkaido.

It is one of 158 uninhabited islands in 22 prefectures that were given names by the government in 2014 to clearly mark Japanese territorial waters.

Under international laws, islands can be designated as such only if they can be seen above the sea surface even in high tides.

If Esanbehanakitakojima has sunk beneath the surface, Japanese territorial waters will shrink.

On the afternoon of Sept. 1, Hiroshi Shimizu, 47, author of “Hito-zukan” (Picture book on hidden islands), visited Sarufutsu to see Esanbehanakitakojima as part of his efforts to write a sequel.

However, he could not find the islet, so he made inquiries to the Sarufutsu village fishery cooperative association.

Tomohiko Kihara, 38, a member of the association’s development research office, who had detailed knowledge of the sea area, studied the situation based on a sea chart.

According to Kihara, Esanbehanakitakojima currently cannot be seen from land nor from fishing boats navigating nearby.

Records show the islet does exist, or at least it did.

“Around a decade from 1975, there was a small island around there, and we stayed clear of the area,” said an elderly member of the fishery cooperative association.

Other fishermen also said they believed that there is an undersea rock reef because an islet is recorded on marine navigation systems.

According to the Japan Coast Guard, Esanbehanakitakojima was surveyed in 1987. Records show the islet jutted 1.4 meters above the average sea level.

The Geospatial Information Authority of Japan described the islet on its map based on a sea chart created in 1988.

“There is a possibility that the islet has been eroded by wind and snow and, as a result, disappeared,” Tomoo Fujii, a senior official of the coast guard, said.

The coast guard plans to investigate the area also to ensure safe navigation of vessels.