Title: Enhancing vessel monitoring systems (VMS) in Sierra Leone to combat IUU fishing.

Illegal, Unreported, and Unregulated (IUU) fishing poses a significant threat to marine ecosystems, fisheries sustainability, and food security in Sierra Leone. In response, the Government of Sierra Leone established the Joint Maritime Committee (JMC) in 2006 and introduced a Vessel Monitoring System (VMS) as a mandatory licencing requirement for industrial fishing vessels. This study assesses the effectiveness of VMS in combating IUU fishing and examines opportunities to improve the utilisation and accessibility of VMS data for enforcement, policymaking, and research. A mixed-methods approach was employed, combining structured questionnaires administered to Joint Operations Centre (JOC) operators and fisheries inspectors with key informant interviews involving the heads of key JMC institutions (n = 15). Quantitative data were analysed using descriptive statistics, and qualitative data were examined through thematic content analysis. The results indicate that respondents perceive VMS as having a high impact on reducing IUU fishing incidents, particularly by enabling vessel tracking, identifying incursions into restricted zones, and supporting targeted enforcement. VMS data were rated as highly useful for enforcement and policymaking, with moderate scope for improvement in research applications. Compliance among industrial fishing vessels was perceived as high, influenced by continuous monitoring, substantial financial penalties, and coordinated interagency enforcement. However, institutional challenges, particularly high staff attrition within the JMC, were identified as key constraints on sustained VMS effectiveness. Therefore, strengthening institutional capacity, improving staff retention, and enhancing data accessibility are essential to maximise the long-term contribution of VMS to fisheries governance in Sierra Leone.