The perceptions of resource users towards any conservation policy can be a major determinant of its success. While co-management policy can enhance the management of fisheries, to date there have been few reports concerning how engagement in co-management regimes may affect fishers' perceptions. This paper assesses the determinants of fishers' environmental perceptions within a co-management regime in Chile. Group meetings and structured questionnaires showed fishers' environmental perceptions were composed of four domains of concern, termed ‘water pollution’, ‘stock conservation’, ‘conservation/profit trade-offs’ and ‘charismatic species’. Fishers' dependence on diving and/or the length of time fishers had engaged with the policy affected their perceptions of each of these domains. Perceptions of the ‘water pollution’ domain were related to length of time fishers had participated in co-management, probably because fishers gained an increased understanding of the market and its need for unpolluted produce. Attitudes towards ‘conservation/profit trade-offs’ tended to become linked to an increasingly conservation-oriented ethic with increasing time of engagement with the policy. Given that the length of time fishers engaged with co-management differentially affected fishers' perceptions of environmental domains of concern, public officials and funding agencies should be careful not to judge co-management prematurely. It takes time to educate participants and overcome distrust. Through co-management processes in Chile, fishers' environmental awareness increased, and sustainable behaviours may consequently increase in the future.