The design of marine protected areas now typically incorporates socioeconomic data to minimize potential negative impacts on stakeholders. However, these data have limitations that are not well understood. Furthermore, whether the application of socioeconomic data in planning actually reduces avoidable negative impacts on stakeholders is rarely evaluated. This study assessed impacts on commercial fishermen of the rezoning of the Moreton Bay Marine Park, in south eastern Queensland. Specifically, this study (1) compared estimates of opportunity costs of new no-take zones from before and after the rezoning was implemented, and (2) identified impacts of the new zoning scheme on fishing businesses and changes to working environment. Although estimates of aggregated opportunity costs before implementation matched those reported afterwards, these costs varied strongly between types of fisheries and individual fishing businesses. A large proportion of fishermen reported loss of fishing grounds. Some have found new grounds but reported that their travel times have increased and that the remaining open grounds are overcrowded. Fishermen have attempted to adapt to this new situation by changing the time spent fishing or diversifying into other fisheries, which required investing in new gear. The effectiveness of a structural adjustment package to compensate fishermen and minimize displacement of effort was limited by poor information on the number and use of commercial fishing licences and little understanding of the dependence of individual fishing businesses on particular fishing grounds. Ways of improving fisheries data for conservation planning and designing adjustment packages to more effectively mitigate impacts of MPAs on commercial fishermen are suggested.