Abstract
Diadromous fish such as Petromyzon marinus and Alosa alosa support economically and culturally important small‐scale fisheries in Portugal but face increasing pressures such as habitat degradation, climate change, and overexploitation. In response, a voluntary label‐of‐origin system was introduced in selected river basins to enhance product differentiation and improve traceability. This study evaluates the implementation and performance of this initiative in the Mondego and Vouga river basins. A mixed‐methods approach combined analysis of labeling records with stakeholder interviews and questionnaires, complemented by a multi‐criteria assessment of implementation challenges. Results indicate generally positive stakeholder perceptions regarding trust and market valorization; however, adoption remained inconsistent and highly dependent on institutional facilitation. Key constraints included limited traceability information, operational difficulties in tag application, and fragmented governance responsibilities. The findings suggest that while voluntary labeling initiatives may enhance product transparency and perceived value, their effectiveness depends on operational feasibility, regulatory integration, and sustained institutional support. This case study provides empirical insights into the opportunities and limitations of traceability‐based instruments for governance and management in inland small‐scale fisheries.