Abstract: Regional fisheries management organizations (RFMOs) function as regional eco-scalar fix to mediate spatial production contradictions in modern fisheries governance by dynamically matching ocean scales and management authority. In order to explore the opportunities and challenges of multi-scalar regional mechanisms in flexibly managing shared biological resources, this paper leverages the theory of scalar politics to examine how RFMOs employ scalar strategies represented by upscaling, downscaling, and rescaling under the international law of the sea. The size of physical space, the hierarchy of organizational space, and the scope of expressional space are analyzed respectively. Through various scalar strategies, RFMOs negotiate power legitimacy and rebalance the relations among fisheries actors to maintain or reshape power dynamics within scalar processes. It is found that RFMOs are characterized by overlapping geographical mandates, increasing tensions between horizontal and vertical hierarchies, and differentiated approaches between stronger and weaker stakeholders in their scalar management of shared fisheries. From flexible membership and participation models to diverse decision-making mechanisms, fisheries actors manipulate institutional scales to align with their interests, leveraging scalar cooperation or contention to rescale power relations. Driven by emerging governance dynamics, notable trends are displayed in the expanded functions, institutional modernization, refined zoning, mosaic membership, dynamic resource allocation, balanced conservation equity, and small-State clubbed governance within RFMOs. While multi-scale collaboration promotes inclusivity, it can also fragment authority and reduce efficiency. As global ocean governance enters a new phase, restructuring fisheries governance will require not only scale adjustments in existing RFMOs but also strengthened supervision in unregulated high seas beyond RFMOs jurisdiction. Fisheries actors can further apply scalar strategies to improve influence, institutionalize proposals, and recalibrate power dynamics, while multilateral mechanisms remain essential for countering the unilateral expansion of extraterritorial jurisdiction and preserving the integrity of global governance systems.