Stakeholders have different educational backgrounds, personal experiences and priorities that contribute to different perceptions about what causes natural resource decline and how to sustain a resource. Yet stakeholders have a common interest, which is to keep the resource of interest from declining. Effective co-management requires sharing of perceptions pertaining to the sustainability of a resource and making decisions that benefit all stakeholders. Therefore, this study used modified causal networks, referred to here as mental models, to elicit and compare stakeholder perceptions about fish decline in the Danajon Bank, Philippines. Perceptions were elicited from three types of stakeholders, each composed of two or three elicitation groups: fishers, local government and environmental organizations. Data were also elicited through semi-structured discussions to investigate why perceptions differed and how stakeholders communicated with one another. Hierarchical clustering revealed two broad clusters of similar perceptions about drivers of fish decline: one being environmental groups and the second being local government and fisher groups. Stakeholder communication patterns revealed that communication was weakest between environmental groups and fishers. A likely contributing factor for the lack of shared perceptions was that knowledge-sharing was constrained by the small number of environmental personnel available to exchange information effectively with the much larger number of fishers and local government personnel. To better co-manage fish populations in Danajon Bank, we suggest modifications to the governance framework to improve knowledge-sharing and social and ecological outcomes.