In an age of dramatic environmental and ecological challenges, the dynamics of sovereignty associated with the conservation of natural resources in Oceania are in flux. This article draws on the transformative work of Tongan anthropologist and political philosopher Epeli Hau'ofa to articulate characteristics of an Oceanian Sovereignty that illuminate ongoing conceptual shifts around conservation in this region. In the wake of intensifying and accelerating environmental challenges from global warming and other hazard drivers, understanding Indigenous peoples and local communities' deeply rooted and emerging perceptions and conceptions of rights over, responsibilities towards, and respect for, nature is a critical context for necessary transformations within conservation science, policy and practice. The articulation of sovereignty that we identify in Hau'ofa sheds light on how Oceania's peoples are asserting rights to make choices about the environmental futures of ocean and island spaces. Oceanian Sovereignty emphasises past, present and future obligations enacted though sustainable use in partnership with an ancestral ocean deeply embedded in cultural identity as a basis of governance rather than in legal and political arguments grounded in the constitutions of states. The resultant nature politics are exemplified in what we term tidal thinking. Tidal thinking refers to Indigenous and local peoples' fluid responses to current challenges around conservation and sustainable management of island and ocean futures and the linked wellbeing of human and non-human entities within them. We conclude with a number of conservation practice, governance, and policy implications that tidal thinking around Oceanian Sovereignty entails.