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Invasive alien species that are brought in from overseas threaten the ecosystem by displacing indigenous species that are unique to Japan. The seriousness of their impact must be recognized once again and measures must be established to prevent the entry and entrenchment of an alien species.
The Environment Ministry has declared the eradication of small Indian mongooses, an invasive species, on Amami Oshima Island in Kagoshima Prefecture.
The mongooses are native to areas from the Middle East to Southeast Asia. They were first introduced to Okinawa Island from India in 1910 with the aim of exterminating species such as habu poisonous snakes. In 1979, around 30 of their descendants were released on Amami Oshima Island.
However, as the mongoose is active during the day, it did not prey on the nocturnal habu. Instead, it attacked native species such as the Amami rabbit, which is designated as a special natural monument of Japan and moves slowly. Efforts to get rid of the mongooses began in the 1990s.
The eradication was successful due to the steady efforts of the local people. A special team was organized, and it continued to capture the animals using cylindrical traps developed by the team, automatic cameras and search dogs that tracked down mongooses.
As a result, the number of mongooses on the island, which was estimated to have reached a peak of 10,000 in 2000, has decreased year by year. As no mongoose has been found since 2018, their eradication was recently announced.
The experience of Amami Oshima Island shows the danger of carelessly bringing in an alien species without understanding the delicate balance of an ecosystem.
Although mongooses have been brought to remote islands in other countries to control rats, there are no successful examples of their eradication in a wide area such as Amami Oshima Island, which has an acreage of 712 square kilometers.
Once an invasive species has established itself, it is difficult to remove it. Since doing so requires a great deal of effort, there are many municipalities that hesitate to carry out eradication efforts. The Amami Oshima case is highly significant in that it showed that eradication is possible if budgets and manpower are secured and animals continue to be captured systematically.
In the northern part of Okinawa Island, where the mongooses still live, there are many precious endemic species such as the Okinawa rail, also known as Yanbarukuina. It is hoped that the central government and local governments will make use of the knowledge and experience accumulated in Amami Oshima Island and aim to eradicate the mongooses in Okinawa Prefecture as well.
The total number of mongooses exterminated on the island is said to have reached 30,000. They had to be disposed of as vermin for the sake of human beings.
On Honshu, the largest of the four main islands of Japan, raccoons native to North America that were imported as pets have gone feral and are causing damage to crops. First, it must be reaffirmed that the principles of “do not allow entry, do not abandon, and do not allow spreading” are important.
