This study examines the relationship between ownership concentration and the management of transboundary ecological processes in the Norwegian salmon industry, focusing on the spread of sea lice, a costly and environmentally damaging parasite. Utilizing the Biomass Herfindahl-Hirschman index as an ownership concentration measure, we assess the extent to which concentrated ownership within production zones (PZs) mitigates the impact of sea lice. Our empirical analysis demonstrates that higher BHHI values are associated with significantly lower sea lice levels. Specifically, a 100-point increase in BHHI reduces the sea lice load per ten fish by an average of 13.56%. These findings suggest that concentrated ownership enhances the coordination of management practices, thereby addressing scale mismatches between property rights and ecological processes. We employ an instrumental variable approach to address potential endogeneity, using variation in ownership structures across PZs. Our results are robust to alternative specifications and highlight the importance of ownership concentration as a governance strategy for managing transboundary externalities in aquaculture. This study contributes to the literature on resource management and provides empirical evidence for aligning property rights with ecological dynamics to achieve sustainable aquaculture practices.