In recent years, China’s and Vietnam’s militarized and subsidized fishing fleets have begun to shift their radical marine harvesting techniques, and accompanying trade, from the South China Sea to Africa and Oceania. Scholarly analysis has largely assumed that fishers are instruments of their states’ geopolitical agendas, responding to regulations and incentives. This both obscures the actual motivations and modalities of fishers’ expansion of their fishing grounds and downplays the transoceanic networks connecting different fishers beyond state territories and localized fishing grounds in past and present. Charting this spike in maritime trespass, TransOcean will analyze and theorize how individuals and groups of fishers move in and out of legal and illegal, state and non-state categories of fisher, poacher, trader and smuggler, and how the emergent mobilities of Asian fishers interact and collide with those of Pacific and African fishers. Deploying the innovative concept of relational and shifting multiple mobilities and employing thalassographic analysis, TransOcean develops a novel theoretical and methodological framework of fishers as mobile maritime actors who exploit their multiple occupations, incomes and networks to pursue transoceanic expansion. TransOcean studies, for the first time, diverse groups of interconnected fishers outside of territorially bounded fisheries and area studies, by analyzing mobilities beyond sea-borne migration or diasporic settlement. Though multi-scalar and globally oriented TransOcean remains firmly rooted in fine-grained ethnography, with a focus on Vietnamese and Chinese and African and Pacific fishers in specific on-shore nodal points, connected by the growing Sino-Vietnamese demand for illicit seafood. Thus, TransOcean breaks new methodological and theoretical ground for tackling intractable marine problems of significant scientific and policy value.