日本におけるカミツキガメおよびワニガメの定着危険性

新聞記事を用いた外来ペットの逸出モニタリング

抄録

Chelydrid turtles, i. e., snapping turtles (Chelydra serpentina) and alligator snapping turtles (Macroclemys temminckii), have been sold as pets and food around the world. It is estimated that tens of thousands of chelydrid turtles were exported from U. S. A. to Japan between 1989 and 2000. Possessing chelydrid turtles has been limited in Japan since 2000 because of the threat to human health. Moreover, because of the threat to native species in Japan, importing and possessing snapping turtles have been banned since 2005. Although feral turtles have often been found in the wild, there are few published data concerning their status in the wild. Review articles describing the current status of feral chelydrid turtles are thus useful to assess the risk of their establishment. I collected records of 208 snapping turtles and 129 alligator snapping turtles from January 1985 to December 2006 using news articles. The number of records of feral chelydrid turtles has been increasing, although laws that limit possession and trade of chelydrid turtles have been promulgated. However, reproductive populations seem to be rare at present because almost all cases were reports of single adult or subadult individuals, not those of hatchlings or juveniles. The risk of establishment of chelydrid turtles will remain for several decades because many turtles imported in the past seem to be still kept in captivity illegally. Utilization of news articles for monitoring feral chelydrid turtles is useful to obtain qualitative information, but we should be cautious in quantitative interpretations of them. We have to plan an effective long-term monitoring system and consider how to treat individuals kept illegally.