The Environment Ministry is close to completing the eradication of invasive mongooses from Amami-Oshima Island, a UNESCO World Natural Heritage site in Kagoshima Prefecture.

The mongooses were originally introduced to reduce the population of poisonous habu snakes on the island, but turned out to be preying on the island's rare endemic species.

According to Shintaro Abe, head of the Amamigunto National Park office, about 30 mongooses were released in the city of Naze, now Amami, in 1979.

However, they were ineffective at eliminating the habu, a type of viper with a high incidence of biting humans, and to make matters worse, they were found to prey on rare species that were easier targets.

The mongooses led to a decline in the population of the Amami rabbit and other endangered native species on the island. On the other hand, the estimated number of mongooses on the island peaked at around 10,000 in 2000, reflecting their high reproductive rate.

Alarmed by the situation, the ministry and local residents began efforts to reduce the mongoose population using traps, sniffer dogs and poison bait under the invasive alien species law, which came into effect in 2005. To date, around 32,000 mongooses have been captured.

Since 2018, sensor cameras installed at about 470 locations on Amami-Oshima Island have rarely captured mongoose. By the end of this fiscal year or later, the ministry is expected to declare the eradication of mongoose complete.

The island is beginning to return to its original state, with the Amami rabbit population estimated to have bounced back to around 20,000 in fiscal 2021, more than eight times the level in 2003.

Meanwhile, mongooses mostly die on the spot after being caught in the traps. "If humans hadn't been involved, they wouldn't have been in this situation," said Abe of the Amamigunto National Park office. "It's our duty as humans to restore nature to the way it was."

"Basic research on mongoose ecology was inadequate" at the time when the mongooses were released on the island, Tomoko Oda of environmental group WWF Japan pointed out. "The tragedy was caused by people only seeing the convenient side" of the mongoose introduction, Oda added.

"The ecosystem is made up of a delicate balance of organisms," said Oda, who works to protect the habitats of endangered species in the Nansei island chain, which includes Amami-Oshima Island.

"We must learn from the loss of mongoose lives and the tears and pain of people involved in the eradication work, in order to prevent the emergence of more alien species," Oda stressed.