This study examines the effectiveness of China's unilateral fishing moratorium in the South China Sea, where unresolved sovereign rights disputes complicate policy enforcement and compliance. Using high-resolution vessel tracking data and causal inference techniques, I identify both intended and unintended impacts of this policy. The findings indicate that while domestic fishing effort within closed areas declines by 84% during the moratorium, regulated vessels' strategic reallocation of fishing activity before and after the ban, along with increased foreign fishing activity during the ban, offsets 60% of the intended conservation gain. Moreover, I find that policy effectiveness fluctuates with external political conditions, as higher compliance coincides with stricter law enforcement and heightened territorial disputes. These findings highlight the challenges of implementing sustainable fisheries management in the absence of clearly defined property rights.