Kashiwajima Island is a small island at the southwest end of Shikoku on the Otsuki Peninsula, within a designated national park. It is connected to the Shikoku mainland by a bridge and can be reached overland. The area is known for encounters with unusual and rare marine life, including juvenile and migratory fish, mouthbrooding jawfish, spawning green squid, and nudibranchs. Divers may also spot locally notable gobies such as the blue-eyed goby and humpback goby, along with other species described as endemic to the island.