Modern Farming Practices in Paddy Fields Negatively Affect an Endemic Frog, Glandirana susurra, in Japan

Paddy fields play an important role as alternative habitats for various wetland-dependent species. Agricultural intensification in paddy fields, however, presents serious threats to these species. Here, we examined the environmental factors, including those related to modern farming practices, affecting the distribution of the Sado wrinkled frog (Glandirana susurra) in paddy fields on Sado Island, Japan. We recorded the abundance of frogs at 42 sites in early and late June 2014 and investigated the species’ responses to several local and landscape-scale variables. We found that frog abundances decreased sharply following the drainage of paddy fields in mid-June and were negatively associated with deep concrete irrigation ditches that surrounded the paddies. The addition of conservation ditches built into rice paddy fields, however, was shown to mitigate against the effects of the drainage. Our results suggest that conservation ditches serve as refuges for G. susurra. We propose that decreasing the depth of irrigation ditches or providing structures for frogs to use and traverse the ditches could be useful approaches that help conserve G. susurra. We also suggest the increased use of conservation ditches and implementation of aquatic biotopes in the surrounding landscape might serve to aid this species’ long-term conservation.