The European Union (EU) promotes a sustainable blue economy in the coastal and marine regions. In Finland, the regional development objectives are defined at the national and regional levels. Maritime spatial planning (MSP) is a tool to reconcile the sea’s different uses. This study considers developing collaborative practices in regional planning to help meet regional development objectives. The MSP participants representing the coastal fishery (fishing and fish farming) in the Satakunta region, Finland, exemplify a local stakeholder group. Coastal fishery is a demanding and highly regulated livelihood, with the potential to grow as local food is trending. A mixed-method approach was used to examine MSP participants’ and fishery experts’ perceptions about regional cooperation and the MSP process. The semi-structured interviews focused on three main themes: regional cooperation and synergies, conflicts and threats, and interest in regional collaboration or establishing secondary businesses. Questionnaires 2019 and 2021 examined stakeholders’ engagement (intrinsic motivation) and social trust towards the planners in the MSP process. The need to tackle the challenges of coastal fishery dictates coastal fishery participants’ perceptions regarding the fishery business’s development in a regional context. Despite the collaborative approach, the first Finnish MSP round did not make a significant difference in the coastal fishery’s status as a stakeholder group. MSP processes and developing the sustainable blue economy are part of the regional development framework, requiring a level playing field and mutual trust among stakeholders. The regional development of marine and coastal areas would benefit from a joint forum for stakeholder interaction built upon MSP. Collaboration could strengthen the integrative and comprehensive management of sea uses and resources.