In 2009, the European Commission set restricted fishing areas northwest of the British Isles to protect deep-sea vulnerable marine ecosystems and fish stocks. Two protection areas which, historically, have been targeted by fisheries directed at blue ling (Molva dypterygia), were defined. The study aims to assess the effectiveness of restricting fishing activity within the protection areas during the blue ling spawning period (March–May) and to determine whether the existing boundaries are fit for purpose. Estimations of the spatial apportionment of blue ling landings within and outside the protection areas are achieved by combining low-resolution data from fishing vessel logbook entries with higher-resolution vessel monitoring system (VMS) data. High-resolution spatial apportionment of blue ling landings is limited by a lack of high-resolution logbook data, and certain assumptions need to be made on whether vessels are engaging in fishing activity at any individual VMS data point, based on vessel speed and types of fishing gear available. Although current measures appear to have influenced fishing activity in the vicinity of the protection areas, more evidence is needed for a robust evaluation of their effectiveness in protecting blue ling. Recommendations are made for improvements in data collection methods and data availability for research in support of monitoring, assessment and delineation of marine protection boundaries.