Assessment for seawall modifications to mitigate land crabs roadkills from field experiments and agent-based modeling

The seawalls and roads between the habitats and intertidal zone impede the migration of land crabs to their spawning sites and increase the risk of roadkill in Gaomei Wetland. A pilot project aimed at mitigating roadkill risk involved modifying the landside of the seawalls from vertical to sloped. The effectiveness of the seawall modification needs to be further assessed. Agent-base modeling (ABM) can be used to estimate the behavioral patterns of organisms under various roadkill mitigation scenarios. The purposes of the present study are to comprehensively assess the difference of climbing behaviors and roadkill events of land crabs before and after seawall modification by field experiments and ABM. The experiments for climbing willingness of land crabs on both vertical and sloped were conducted. Three years' roadkill observations were surveyed during breeding seasons before and after seawall modification. Scenarios with different proportion of vertical and sloped seawalls were simulated using ABM. The behavioral experiment results showed that crabs have higher climbing willingness on the sloped seawall compared to the vertical seawall. The ABM simulation results indicated that the proportion of individuals remaining on the ground decreased by 28 % after seawall modification, similar to the field survey results. The simulation also indicated the importance of identifying the roadkill hotspot. The results suggested that the seawall modification increased the climbing willingness and mitigated the roadkill risk. The methodologies and findings from the field experiments and ABM simulation in the present study provide comprehensive approaches for assessing the effectiveness of roadkill mitigation measures.