Over-fishing is a global problem that damages the marine environment and compromises the long-term sustainability of fisheries. This damage can be mitigated by restricting catch or other activities that can occur in marine areas. However, such management is only effective when restrictions are enforced to ensure compliance. We expect fishers to help enforce restrictions when they have exclusive user rights and can capture the benefits of management. In a number of such cases, however, fisher participation in the enforcement of user rights is absent. In this analysis we used Chile as a case-study to investigate why fishers do not participate in enforcement even when they have exclusive territorial user rights (TURFs). We used a best-worst scaling survey to assess why fishers would choose not to participate in enforcement through monitoring their TURF management areas, and what would help to increase their participation. We found that the main reason fishers do not monitor is because they consider government policing of marine areas and punishment of poachers to be ineffective. Increased and timely responsiveness by government when poachers are detected and more stringent penalisation of poachers may lead to greater involvement in enforcement by fishers.