# Impact of the July 2018 Heavy Rain Disaster on the Endangered Nagoya Daruma Pond Frog (Pelophylax porosus brevipodus) in Rice Fields of Mabi Town, Kurashiki City, Western Japan: Changes in Population Structure over Five Years

## TL;DR

A 2018 flood in Japan severely impacted an endangered frog species, but its population partially recovered after rice fields were restored.

## Contribution

This study provides empirical evidence of habitat recovery effects on an endangered frog after a natural disaster.

## Key findings

- Frog numbers dropped sharply after the 2018 flood but showed recovery in 2021 with rice cultivation resumption.
- Population fluctuations continued in 2022, indicating ongoing challenges for full recovery.
- Restoring rice fields is crucial for the survival of the Nagoya Daruma Pond Frog after disasters.

## Abstract

The Nagoya Daruma Pond Frog is an endangered species that inhabits rice fields in western Japan. In 2018, severe flooding damaged many rice fields in Okayama Prefecture, disrupting the frog’s habitat. By comparing surveys conducted before and after the disaster, we observed changes in the number and size of frogs, along with signs of recovery once rice farming had resumed. This study highlights the importance of maintaining and restoring rice fields after natural disasters to conserve endangered species like this frog.

Rice paddy fields (referred to below as rice fields) are important not only for food production, but also as habitats for various species. The Nagoya Daruma Pond Frog (Pelophylax porosus brevipodus) is an endangered frog species endemic to Japan, mainly living in and around rice field areas. In July 2018, heavy rainfall caused severe flooding in Mabi Town of Okayama Prefecture, western Japan, submerging numerous rice fields and affecting local frog populations, including P. porosus brevipodus. To clarify whether the population structure of P. porosus brevipodus changed following the flood disaster in the rice fields of Mabi Town, we conducted quantitative field surveys in a rice fallow field in mid-October before (2017) and after (2018, 2020–2022, excluding 2019) the flood. The number of frogs declined sharply after the 2018 flood, reaching only a few individuals by 2020, but showed a substantial recovery in 2021 following the resumption of rice cultivation, although numbers decreased again in 2022. This recovery, despite fluctuations, indicates that habitat restoration through rice farming played a key role in enabling the population to rebound. Our findings underscore the importance of maintaining and restoring rice field environments after natural disasters for the survival and long-term recovery of P. porosus brevipodus.