Territorial use rights in fisheries (TURFs) represent a form of spatial co-management to secure access rights for communities while simultaneously supporting marine conservation. In Ecuador, a TURF system emerged in many mangrove-associated fisheries after the government enacted legislation in 1999 favoring decentralized mangrove conservation. In communities where custodias (mangrove concessions) were implemented, members of local fishing associations have defined access privileges for certain fisheries within the boundaries of their concession. The present study explores the tradeoffs that emerged through the interaction between informal customary norms in fishing and the formal TURF system associated with custodias. Combining fishery data and ethnographic insights about Ecuador’s fishery for mangrove cockles Anadara tuberculosa (G. B. Sowerby I, 1833) and Anadara similis (C. B. Adams, 1852), I evaluate outcomes of fisher empowerment, perceptions of success, fishery productivity, and tradeoffs. I argue that empowering fishers with stewardship rights is critical for successful TURFs in Ecuador. Custodias have strengthened access rights and created conditions that promote habitat health with implications for fishery productivity and economic benefits derived from larger catch and shell sizes. On the other hand, custodias limit access and fisher mobility, resulting in the reconfiguration of fishing space and displacement of independent fishers from their customary grounds. Moreover, secure access rights do not necessarily provide incentives for individuals to harvest shells according to the size regulations imposed by current policies. Understanding the benefits and limitations of this integrated approach to coastal management may provide valuable insights for other forms of spatially-explicit marine governance and fisheries co-management.