Declaration of the Eradication of the Small Indian Mongoose (Designated Invasive Alien Species) in Amami Oshima Island

The small Indian mongoose Urva auropunctata is a type of carnivorous Herpestidae family and originally ranges from the Middle East, southern China, and south Asia.

The body length of males and females is 60 cm and 50 cm, respectively, and the small Indian mongoose is slightly bigger than the Japanese weasel. The mongooses become pregnant in the breeding period 1 year after their birth (mainly in March ~ September in Amami Oshima Island) once or so a year and give birth to 2~7 litters per birth (average: 2.26 litters).

The small Indian mongooses (hereinafter referred to as the “mongooses”) eat diverse types of animals from small invertebrates such as grasshoppers and crickets to vertebrates such as frogs, rats, and rabbits. The distribution area of the mongooses extended in Amami Oshima Island and the number reached approx. 10,000 by the year 2000 (6,000 (estimation at the end of FY1999) + natural increase) and their presence had a significant impact on endangered native animals such as the Amami rabbit and the Ryukyu long-furred rat. The mongooses were designated as invasive alien species under the Act on the Prevention of Adverse Ecological Impacts Caused by Designated Invasive Alien Species (Act No. 78 of 2004, hereinafter referred to as “Invasive Alien Species Act”).

The mongooses were introduced to Okinawa Island in 1910 and gained a foothold. Then, around thirty mongooses were brought to Amami Oshima Island from Okinawa Island in 1979. According to interviews with parties concerned, they were released near Asani-Akasaki in Naze City.

As the distribution of the mongooses that gained a foothold extended, the damage of agricultural and livestock products began to be observed. In response, the municipal governments started to capture the mongooses as harmful wildlife in 1993. The Ministry of the Environment (then Environment Agency) and Kagoshima Prefecture started to investigate the distribution and number of mongooses and examine a way of capturing them as a model project for 4 years from 1996. As a result of this model project, it was revealed that the distribution area of many native species including the Amami rabbit was diminishing in response to the expanded distribution of the mongooses and that urgent measures were required. That is why the Ministry of the Environment (then Environment Agency) and Kagoshima Prefecture commenced an eradication project (scheme in which incentives are provided according to the number of mongooses captured) in 2000 (the Environment Agency has been conducted the project alone since 2001).

However, the home range of the mongooses is so small that their distribution area did not decrease only by capturing them along the roads. Therefore, it was necessary to place traps more precisely including forests with the aim of eradicating the mongooses.
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Since the Invasive Alien Species Act was enacted in 2005 and the mongooses designated as Designated Invasive Alien Species, the Environment Agency formed a professional group named “Amami Mongoose Busters” to strengthen the control program. Since then, the Amami Mongoose Busters has played a central role in placing and managing over 30,000 traps and over 300 camera traps at high densities in almost all areas of Amami Oshima Island including forests, introducing Mongoose detection dogs, and using rodenticides in places other measures are difficult to be taken in the last phase of the project. Moreover, the Amami Mongoose Busters has taken all possible measures to control the mongooses by improving traps repeatedly to avoid bycatch and by developing a method of capturing them in coordination between detection dogs and their handlers.
  Amami Mongoose Busters
  Logo of Amami Mongoose Busters

These organized, long-term, and tireless efforts, the preparation and management of progress of control plans based on scientific knowledge, and the coordination with many supporters including residents have produced fruit and the number of mongooses has been reduced significantly in tandem with the progress of the control project. Since the last one mongoose was captured in April 2018, no clear information on inhabitation has been confirmed such as that a mongoose was captured by a trap, detected by a Mongoose detection dog, or shot with a camera trap.
  Figure 1  Estimated number of mongooses (Line graph: black dotted lines refer to 5% and 95% CI, while black solid line refers to 50%), number of mongooses captured (Line graph: red solid line), and capturing effort (Bar graph: (light blue) number of days in which live animal cage traps were placed, yellow-green: Number of days in which kill traps were placed)

The same effort for searching and capturing the mongooses has been made by FY2023 even after the number of mongooses captured reached zero in Amami Oshima Island. However, it is extremely difficult to confirm that a specific species has been eradicated from one region so that it cannot be determined that eradication is achieved when the number of captured animals becomes 0. Therefore, two calculation models of eradication probabilities were created (Harvest-based model (HBM: Area-based) and Rapid Eradication Assessment (REA: number-based) as the methods of evaluating eradication probabilities of the mongooses.*

The eradication probabilities of mongooses of HBM and REA showed 99.7% and 98.9%, respectively, according to the evaluation results taking into account confirmed data on eradication works carried out by the end of FY2023. Taking into account the evaluation made by the experts based on these results that it is appropriate to conclude that the mongooses have been eradicated, upon consultation with related administrative agencies, the Ministry of the Environment decided to declare that the mongooses have been eradicated from Amami Oshima Island on September 3, 2024.

* Created through the Environment Research and Technology Development Fund implemented between FY2020 and FY2022 to “enhance technologies for the control policy decision process of invasive alien mammals (Representative: Professor JOGAHARA Takamachi of Okinawa University)”
  Figure 2  Eradication probabilities calculated by the two calculation models: HBM and REA

There are nine islands where the mongooses were eradicated successfully all around the world prior to the case of Amami Oshima Island. Among them, the largest island where the breeding population of mongooses that gained a foothold for a prolonged period is Fajou Island (Barun et. al., 2011). The eradication of the mongooses in Amami Oshima Island which is much larger than those islands is the first important achievement in terms of biodiversity by people and organizations committed to eradicating the mongooses for about 25 years.

After the mongooses were introduced, the distribution area of native various species has diminished along with the expansion of the number of mongooses and their distribution area. However, as the mongoose control progressed, the status of inhabitation of some species started to improve. For example, the number of Amami rabbits, Amami tip-nosed frogs, Otton frogs, and Amami Ishikawa’s frogs (Watari et. al., 2013) as well as the number of Amami spiny rats and Ryukyu long-furred rats (Fukasawa et. al., 2013) showed a recovery trend. Since then, it has been seen that the distribution area of various species has expanded also in the case of Amami thrushes (Mizuta et.al., 2017) and Amami woodcocks (Amami Animal Wildlife Center Ministry of the Environment, data unannounced). The control and eradication of the mongooses are believed to have made a significant contribution to improved ecosystems in Amami Oshima Island.

Amami Oshima Island became a world heritage site in July 2021 as “Amami-Oshima Island, Tokunoshima Island, Northern part of Okinawa Island, and Iriomote Island,” because of its rich biodiversity represented by internationally appreciated native species. The recovery of native species is believed to have made a significant contribution to the conservation of Amamigunto National Park including Amami Oshima Island and this registration as a world heritage site.

As a result of the eradication of the mongooses, the damage of agricultural and livestock products caused thereby disappeared. Moreover, because a sightseeing tour to observe fauna and flora of the island is the main pillar of tourism, the recovery of native species is believed to have a positive impact.
  Figure 3 Change in the frequency of shooting by camera traps installed by the Amami Mongoose Busters (Number of photos taken per day/1,000 cameras). It is difficult to take note of changes in the number of Ryukyu long-furred rats and Owston’s white-backed woodpeckers compared to other species, because they are captured less frequently by cameras installed on the ground.

When we aim to eradicate any invasive alien species, it is essential to acquire an understanding of biology of the target species and constantly monitor and evaluate whether sufficient measures for eradication are being taken. For example, it should be evaluated whether current control works cover the entire distribution area, whether the expansion of the distribution area is controlled, and how these control measures contribute to the decrease in the number of animals. The fact that it was possible to eradicate the mongooses in a big island with uphills and downhills as well as complex terrains like Amami Oshima Island is expected to serve as an excellent example for national and international measures against alien species in the future and contribute to the promotion of such measures.
On the other hand, if the mongooses were not introduced in the first place, many parties concerned would not have any trouble worrying about the damage caused by the mongooses and how to capture them for such a long time. We are responsible for complying with the three principles for preventing the damage caused by alien species, namely, “Do not introduce, release, or spread” in order not to bring about the second mongoose.

Reference

• Amami Wildlife Conservation Center Website (in Japanese)
  https://kyushu.env.go.jp/okinawa/awcc/index.html