Amami-Oshima is registered as a UNESCO Natural World Heritage site. Mongooses preyed on the island's rare native species.
Ministry officials say it is a rare accomplishment to eliminate mongooses from wide areas where they have become firmly established.
Tenacious efforts were key to success
Officials said no mongooses have been trapped for more than six years, nor has the animal's image been captured by any of the motion sensor cameras installed at 579 locations on the island.
Based on this data, experts concluded it's highly likely that mongooses have been eliminated from the island.
Ueda Akihiro, director general of the ministry's Nature Conservation Bureau, then officially declared the non-native species had been eradicated from the island.
Environment Minister Ito Shintaro told reporters that tenacious efforts were key to the eradication.
Amami Mongoose Busters
According to the ministry, 30 mongooses were introduced to Amami-Oshima in 1979 to exterminate the habu snake, a poisonous pit viper.
There was a problem, however. Mongooses are diurnal while habu snakes are nocturnal, so there was limited contact between them.
Instead, mongooses began preying on rare native species including the Amami rabbit — a highly protected species that has been designated as a "special natural monument."
The island's mongoose population burgeoned to an estimated 10,000 by 1999.
In 2005, the ministry designated mongooses as an alien species harmful to the ecosystem and launched a project to eradicate them.
Local residents and others formed the Amami Mongoose Busters group to capture the mongooses. They set 30,000 traps and also used dogs to locate the animals.
Watari Keita of the Amami Mongoose Busters says the group has worked to bring the island closer to its original state.
He adds that the mongoose busters had to go deep into the forest to capture the animals, which was dangerous work, and the heat made the effort all the more challenging.
Watari says he's happy that the rabbit population has increased and feels a sense of accomplishment.
Don't import alien species
Ishii Nobuo, a professor emeritus at Tokyo Woman's Christian University, says it is amazing that the extinction of native species by an alien species has been prevented.
But the Environment Ministry says it's possible mongooses could still arrive from the main island of Okinawa, where they were also introduced to control the habu population. Ministry officials say they will continue to use motion sensor cameras to monitor for the animals.
Another expert says feral house cats also attack the island's native species. He adds that South East Asian frogs — another alien species — have been spotted and they could impact the island's ecosystem as well.
The environment ministry is asking local residents to take proper care of their pets.
It's also calling on the public to follow three rules to avoid damage by alien species: no importation, no release, no spreading.