Takashi Shibazaki, 31, a fisherman based on Chichijima about 1,000 km south of Tokyo, saw a suspicious foreign boat in mid-March near the island.

Shibazaki's tuna fishing boat approached the ship and came within about 10 meters before the foreign vessel started moving toward the high seas.

That was only the beginning. Throughout the month, many local fishermen saw similar foreign ships, each apparently weighing 100 to 200 tons, near Chichijima, which is part of the Ogasawara Islands and is under the jurisdiction of the Tokyo Metropolitan Government.