This paper investigates the dynamics of institutional development and co-management performance in small-scale fisheries. The study covers different contexts and spatial and temporal scales, for nine case studies in the South Pacific. In these cases, new co-management institutions were intentionally set up from 2008 to 2016 through fishery policy intervention to address over-exploitation problems of sea cucumber resources. This was carried out in a process of adaptive experimentation, based on a collaborative and problem-solving approach to governance, and a context-based vision of sustainability issues. In order to quantitatively and empirically assess change in governance within and between cases, a multidimensional analytical framework of governance performance is developed. A set of governance performance criteria is defined and the criteria are scored using data from an institutional diagnosis of the cases, throughout the research period. Ten out of eleven criteria were positively impacted by the co-management interventions. Three institutional development trajectories can be identified for the fishery co-management building process, involving a range of gradual and abrupt changes. Consolidation of the institutional changes achieved by the interventions is required to successfully develop the resilience of the fishing systems to multiple stresses. This empirical study provides a methodology for systematically assessing institutional dynamics in fisheries, and in particular the crafting and sustaining of co-management regimes in small-scale fisheries. The approach could potentially be applied to other complex social-ecological systems.