Kojima (Hokkaido)
Ko Island or Kojima is an uninhabited island in the Sea of Japan, southwest of the mainland portion of the town of Matsumae and is the southernmost point in Hokkaidō. It is under the administration of the town of Matsumae in Oshima Subprefecture in Hokkaidō, Japan. To distinguish Ko Island from other islands with the same name, it is sometimes known as Oshima Ko Island or Matsumae Ko Island.
Ko Island has an area of. It is an andesitic stratovolcano. The peak consists of non-alkali mafic rocks, dating from the Early Pleistocene overtop of non-alkali felsic rocks from the Late Miocene-Pliocene.
Several smaller islets surround Ko Island, including Daihiyakushima, Shohiyakushima, Tenjinshima, and Sazaeshima.
To provide refuge for fishing vessels, a small harbor has been put in place.Ko Island has been designated a natural monument. It is a breeding ground for common guillemot, Japanese cormorant, and black-tailed gull.
to the west of Ko Island is the Ko Island Bank, where migratory fish tend to gather. In the adjacent seas there is also tuna and squid. In previous times it was referred to as the Sea of Treasure. For this reason it is a major fishing area for fishermen out of Matsumae, especially because of the decline in the Arabesque greenling over the last 24 to 25 years.
The predominant vegetation on the island is grasses, but there are stands of Acer pictum subsp. mono in the caldera.
