|Native name: 小島, Ko-jima|
|Area||1.54 km2 (0.59 sq mi)|
|Coastline||5 km (3.1 mi)|
|Highest elevation||282.1 m (925.5 ft)|
|Highest point||Ko Island|
Ko Island (小島? Ko-jima) or Kojima is an uninhabited island in the Sea of Japan, 23 kilometres (14 mi) southwest of the mainland portion of the town of Matsumae town and is the southernmost point in Hokkaidō. It is under the administration of the town of Matsumae in Matsumae District, Oshima Subprefecture in Hokkaidō, Japan. To distinguish Ko Island from other islands with the same name, it is sometimes known as Oshima Ko Island (渡島小島? Oshima-Kojima) or Matsumae Ko Island (松前小島? Matsumae-Kojima).
Ko Island has an area of 1.54 square kilometres (0.59 sq mi). 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.
Flora and fauna
15 kilometres (9.3 mi) 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 (宝の海? Takara no Umi). 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.
- 地図閲覧サービス 2万5千分1地形図名： (内挿図又は図葉外）. 25,000:1 Topographical Map (in Japanese). Geographical Survey Institute. Retrieved 2008-12-14.
- 小島漁港の概要 (in Japanese). Hakodate Development and Construction Department. Retrieved 2008-12-14.
- "OSHIMA KO-JIMA". Quaternary Volcanoes of Japan. Geological Survey of Japan, AIST. 2006. Retrieved 2008-12-14.
- "Hokkaido". Seamless Digital Geological Map of Japan. Geological Survey of Japan, AIST. Nov 2, 2007. Retrieved 2008-12-14.
- "JP031Matsumae islets". Important Bird Areas in Japan. Wild Bird Society of Japan (WBSJ). 2009. Retrieved 19 January 2010.
- Based on the translation of ja:渡島小島 on 14 December 2008