Managing industrial fisheries presents a persistent and complex sustainability challenge. Despite the establishment of comprehensive regulatory frameworks, international agreements, and voluntary certification schemes, fisheries worldwide continue to face overfishing, illegal practices, weak governance, and contribute to habitat degradation. Rather than discrete or isolated problems, industrial fisheries are better conceptualised as nested collective action dilemmas, in which environmental externalities emerge from decisions made by diverse actors operating across multiple governance levels. Actions taken by individual fishers, firms, or governance institutions often produce cascading effects that cross spatial and institutional boundaries, further complicated by the mobility of marine species and the transboundary nature of marine ecosystems. This thesis explores how voluntary collective action, inspired by stewardship aspirations, can contribute to more sustainable fisheries governance. Comprising four papers grounded in social-ecological systems thinking, it examines diverse efforts to coordinate sustainability commitments among industry actors. Paper I traces the evolution of seafood stewardship over the past five decades and identifies four dimensions that enable collective action: moving beyond compliance, adopting systems perspectives, embracing uncertainty, and recognising the embeddedness of humans in the biosphere. Paper II investigates pre-competitive collaborations as voluntary sustainability initiatives, focusing on their design and regulatory fit, but also their frequent lack of enforcement and systematic evaluation. Paper III employs process tracing in the Barents Sea cod fishery to examine how critical events shaped and were shaped by social relationships in the development and institutionalisation of collective action. It highlights the role of Interaction Rituals and trust-building in influencing governance outcomes. Paper IV addresses the governance of transshipment, a contested practice often linked to illegal fishing, by mapping the ownership of refrigerated cargo vessels. It argues that a nested governance approach, combining formal regulation with voluntary initiatives, provides new and innovative ways of governing this practice. Together, these papers suggest that voluntary collective action can effectively complement state-led governance when underpinned by trust, transparency, and accountability. Due to the complexity of industrial fisheries, achieving sustainability will require hybrid governance structures that combine stewardship-focused cooperation with strong regulatory institutions.