Countermeasures required for invasive deer in the northern part of Okinawa's main island

A research team composed of Assistant Professor Shun Kobayashi of the Biology Program, Department of Chemistry, Biology and Marine Science, Faculty of Science at the University of the Ryukyus, including the researchers from the Okinawa Churashima Foundation, Nansei Environmental Laboratory, Co., Ltd., and Forestry and Forest Products Research Institute, has announced that by analyzing the feces of the Japanese deer, a domestic alien species that has been spotted in the forests of the World Natural Heritage Area in Yanbaru in northern Okinawa, also eats endangered species. This was found by using the DNA metabarcoding analysis method. The risk of invasion of non-native species into the World Natural Heritage Areas became apparent. The results were published in Mammal Study published on March 13.

In October 2024, a deer was spotted on a prefectural road running through the World Natural Heritage Area of Yanbaru in northern Okinawa main island. The area is globally known as a home for many endemic and endangered species.

Two days later, a single deer fecal pellet that was found near where the deer was spotted was collected and studied. According to the study, the deer was genetically a Japanese deer strain originating from Kinkazan Island in Miyagi Prefecture, and this individual had been anthropogenically introduced from the outside. Since large herbivores such as a deer are not distributed on the island of Okinawa, the Japanese deer is a domestic non-native species.

To clarify the plants foraged by this Japanese deer, the DNA metabarcoding analysis method was used on the same fecal pellet. As a result, 28 plant species in total were detected, including 24 species of angiosperms and 4 species of ferns. Included among the plants was Gardneria liukiuensis (Ryukyu hourai kazura), a species classified as category IA (very high risk of extinction in the very near future) in the Red Data Book of the Ministry of the Environment.

G. liukiuensis is an endemic species that grows on limestone rocks and trees in the Central Ryukyu Islands, distributed only in northern Okinawa Island, Tonaki Island, Okinoerabu Island, and Kikai Island. Because of limited habitat, even a small amount of foraging could have a significant impact on the survival of the population.

In Japan, currently, there are no laws or regulations that control domestic invasive alien species. A system to control the Japanese deer and prevent the invasion of new domestic alien species into World Natural Heritage Areas needs to be established as soon as possible.

Kobayashi said, "In this study, 28 plant species were detected in only 5 fecal pellets, which indicates the magnitude of the impact of non-native large herbivores. I believe that because of this study, who is responsible for controlling domestic invasive species and responding to their escape has come to light as a problem that needs to be solved. I hope that measures will be established to prevent an event like this from occurring in the future."

Journal Information
Publication: Mammal Study
Title: Foraging of Endangered and Endemic Plant Species by a Non-Native Sika Deer Found in the Northern Part of Okinawa-Jima Island, Japan: Evidence from Fecal DNA Metabarcoding Analysis
DOI: 10.3106/ms2025-0049