Traceability is broadly understood as a technical means of understanding, communicating and steering the relations of production and trade in the global food system. Using an assemblage lens, this paper challenges this technical understanding by analysing how traceability affects and is affected by the relations that constitute global value chains. Analysing the introduction of the ThisFish traceability system in a small-scale tuna fishery in Indonesia we show how an NGO, Masyarakat dan Perikanan Indonesia (MDPI), de-stabilised existing relations and expertise around landing and trading tuna and subsequently re-stabilised these relations in a different assemblage through the collection, collation and management of fisheries data. In doing so MDPI worked through rather than reconfigured the social relations of production and trade in the implementation of traceability, thereby becoming part of the assemblage the NGO sought to change. The results demonstrate how the implementation of traceability is, in contrast to its technical framing, more accurately understood as a process of 'active embedding' by 'boundary subjects' who re-assemble contingent interactions by enacting multiple roles simultaneously. Traceability is as such contingent on the performance of these boundary subjects rather than on market incentives or objective monitoring and control. However, we also conclude that because it also dependent on the negotiated identity and function of these boundary subjects, traceability (and similar market based forms of governance) risk reinforcing rather than transforming the relations of production and trade they engage.