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Abstract

Illegal, unreported, and unregulated (IUU) fishing poses a significant threat to fisheries sustainability, global food security, and biodiversity conservation. Many regions rely on patrol-based enforcement to promote compliance, yet the effectiveness of such strategies in deterring IUU activity remains underexplored. In this study, we employed a mixed-methods approach to assess the impact of management and policy decisions on illegal fishing within the Chagos Archipelago marine protected area (MPA). This MPA has maintained near-continuous patrols since its implementation in 2010, providing a unique opportunity to evaluate the influence of patrolling on illegal fishing deterrence. First, we analyzed semi-structured interviews with fishers in Sri Lanka, the origin of most intercepted illegal fishing vessels, to contextualize perceived deterrence within the broader socio-economic environment of the MPA. We then examined patrol vessel movements from onboard automatic identification systems to compare the effectiveness of different enforcement strategies. Finally, we evaluated the relationship between patrol effort and illegal fishing interception rate as an indicator of deterrence. Interviews indicated that strengthened port monitoring and regulatory improvements in Sri Lanka contributed to perceived deterrence. Although variations in patrol strategy significantly affected interception rates through differences in vessel activity and spatial coverage, no deterrence effect of any patrolling strategy was detected. Our findings highlight the value of multidisciplinary approaches in evaluating enforcement effectiveness and emphasize the need for diverse, context-aware policies to address illegal fishing within MPAs that incorporate patrolling, robust national regulations, and community-focused strategies.

Publication Date

2026-03-16

Publication Title

ICES Journal of Marine Science

Volume

83

Issue

3

ISSN

1054-3139

Acceptance Date

2026-02-22

Deposit Date

2026-03-25

Funding

C.K. was funded via a doctoral training grant awarded as part of the UKRI AI Centre for Doctoral Training in Environmental Intelligence (UKRI grant number EP/S022074/1). T.L., C.C., and L.G. acknowledge the support from the Bertarelli Foundation. K.M. acknowledges support of the Convex Seascape Survey, Oceans 5, and Wildlife Conservation Society Congo Programme.

Keywords

Chagos Archipelago, deterrence, enforcement, illegal fishing, large-scale MPA, multidisciplinary, non-compliance

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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