Mauremys reevesii (Reeves’ turtle) is an endemic freshwater turtle species found throughout East Asia. Due to a rapid population decline, the International Union for Conservation of Nature (IUCN) and the Korean government have classified this species as Endangered (EN). The reported largest population size of M. reevesii in the Republic of Korea was previously estimated to be approximately 20-30 individuals. Our study assessed the population size and structure of M. reevesii at Geumho Reservoir, Republic of Korea, using a capture-recapture data. A total of 433 M. reevesii were incidentally captured during a 35-week trapping process conducted from March to October 2023. The sex ratio of the captured population exhibited a male bias of 1.3 : 1. Sexual size dimorphism was observed only in body weight. Individuals were recaptured up to 11 times during the study period, with males and females being recaptured at an average of 2.1±2.0 times and 1.5±0.9 times, respectively. The estimated population size of M. reevesii in Geumho Reservoir was approximately 891 turtles. The absence of notable sexual size dimorphism and significant sex ratio differences suggests that the population in this area may have been established relatively recently. Compared to previous records, the population in Geumho Reservoir represents the largest single population of M. reevesii, both within the Republic of Korea and globally.

Abstract
1. INTRODUCTION
2. MATERIALS AND METHODS
    2.1. Study area
    2.2. Sampling target species
    2.3. Population structure
    2.4. Sexual size dimorphism and analysis
    2.5. Population size estimation
3. RESULTS
    3.1. Population structure
    3.2. Rate of recapture
    3.3. Population size estimation
4. DISCUSSION
5. CONCLUSION
CRediT authorship contribution statement
Declaration of Competing Interest
ACKNOWLEDGEMENTS
REFERENCES
APPENDIX

• Hakyung Kang(Division of EcoScience, Ewha Womans University, Seoul 03760, Republic of Korea)
• Jeong Min Oh(Division of EcoScience, Ewha Womans University, Seoul 03760, Republic of Korea)
• Kyo Soung Koo(Research Institute of EcoScience, Ewha Womans University, Seoul 03760, Republic of Korea, Korean Environmental Geography Institute, Sejong 30141, Republic of Korea) Corresponding author
• Yikweon Jang(Department of Life Sciences, Ewha Womans University, Seoul 03760, Republic of Korea)