Using innovative guidance facilities to reduce roadkill rates during land crab breeding season in Green Island, Taiwan

During the breeding seasons from May to September of 2022 and 2023, a study on land crabs and hermit crabs (hereinafter referred to as land crabs) was conducted in a roadkill hotspot located along the circular road from Shilang to Guiban on the west side of Green Island, Taiwan. Two sets of culverts connecting the mountain side to the sea side under the road were utilized to install guidance facilities, directing land crabs into the culverts to safely cross the road and release their juveniles by the sea. The study aimed to evaluate the effectiveness of these guidance facilities in reducing land crab roadkill rates. The study was divided into control and experimental groups, comprising a total of 54 surveys, with 29 conducted in 2022 and 25 in 2023. Surveys were carried out 26 times in the morning and 28 times at night. A total of nine species of land crabs were recorded, with the highest numbers observed for Metasesarma aubryi , followed by Coenobita brevimanus . The total number of recorded individuals in 2023 was 1258, significantly higher than the 575 recorded in 2022, with peak numbers observed in June, July, August, and September. The utilization rate of the guidance facilities for M. aubryi was significantly higher than that of the control group (P = 0.005), and similarly, the utilization rate for C. brevimanus was significantly higher than the control group (P = 0.038). In 2022, the overall roadkill rate for the experimental group was 8.5 %, compared to 26.8 % for the control group. Similarly, in 2023, the roadkill rate for the control group was 32.1 %, while the experimental group was only 12.1 %. For M. aubryi , the road kill rate in the control group was 41.7 % in 2022 and 45.8 % in 2023, while the experimental group had rates of only 19.4 % and 22.8 %, respectively (P = 0.001). For C. brevimanus , the roadkill rates for the control group in 2022 and 2023 were 4.5 % and 4.3 %, while the experimental group had rates of 0.9 % and 0.4 %, indicating that the experimental group had significantly lower roadkill rates than the control group (P = 0.024). Therefore, in both 2022 and 2023, the experimental group had a roadkill rate reduced by more than half compared to the control group, demonstrating the effectiveness of the guidance improvement measures implemented. Based on these findings, future designs could involve the installation of similar underground culverts and guidance facilities in other road kill hotspots to greatly reduce land crab roadkill rates. • Few studies have evaluated culvert channels' effectiveness in reducing land crab roadkill. • The control culvert was 8.35 m long with no guiding features, the experimental culvert was 8.25 m long with guiding features. • The experimental group achieved a more than 50 % reduction in roadkill rates compared to the control group. • Future designs should consider culverts and guidance systems in other roadkill hotspots to decrease land crab fatalities.