Recent Control of Invasive Alien Animals in the Bonin Islands

Abstract

The Bonin Islands are oceanic islands of Japan that have never been connected to the continent, and include abundant endemic species and ecosystems. These islands were registered as a UNESCO Natural World Heritage Site in 2011, along with other islands of the Ogasawaras. The environment of the Bonin Islands has been disturbed by development and livestock since human settlement began, and many native organisms remain at risk of extinction due to alien species introduced by humans. To conserve and restore the native ecosystems, alien animals (cats, goats, pigs, bullfrogs, and rodents) have been eradicated on several islands through alien species control projects conducted with the cooperation of administrative organs, the private sector, and residents. The outcomes of these projects highlight the importance of understanding the interactions among multiple alien species and considering the indirect effects of alien species control. However, in recent years, further alien species countermeasures have been required for the big-headed ant and land nemerteans, which have been identified as posing an ecological risk, and for a predatory snail that has recently invaded. Control strategies for alien animals are associated with many issues, including legal restrictions, environmental and human impacts, and technical aspects. In particular, it is difficult to eradicate small-sized species that have high fecundity and invade easily. Therefore, for future protection of the Bonin Islands as a Natural World Heritage Site, it is essential to strengthen the quarantine system to prevent alien species from dispersing on other islands, and to prevent new alien species from invading.