I've no idea whether anyone took Japan's move seriously.
Japan has a couple of very tiny islands, each basically no more than a rock sticking a few feet above the ocean surface, with an area measured in sq. yards rather that sq. miles. But they are crucially important because, being far from anything else, they establish a 200-mile fishing zone Japan wouldn't otherwise have. Japan has spent major yen to prevent them from eroding away.
Some are so small as to raise the question, "What is an island?" Specifically, is it considered an island though it is sometimes fully submerged below the ocean surface (at high tide)? I believe it counts if submerged for fewer than 12 hours in each 24. Truly the Talmudic nuance that Inselpeter notes.
