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Acknowledgements The European Maritime Safety Agency (EMSA) is gratefully acknowledged for providing the KLD data and the number of executed fuel samples in the EU. The authors wish to thank Christophe Swolfs and Bart Colaers from the Federal Public Service for Mobility and Transport for their help in obtaining the Thetis-EU data. Acknowledgement to the national competent authorities for their approval to use their RPAS monitoring and port inspection data: the Danish Environmental Protection Agency (EPA), the Danish Mar- itime Agency (DMA), the French General Directorate of Maritime Affairs, Fishery and Aquaculture (DGAMPA), the German Federal Maritime and Hydrographic Agency (BSH), the Human Environment and Transport Inspectorate of the Ministry of Infra- structure and Water Management of the Netherlands (ILT), the Swedish Transport Agency, the Spanish Ministry of Transport, Mobility and Urban Agenda (MITMA). Finally, we wish to thank Rebecca Gualandi for proofreading the manuscript. Author contributions W.V.R. designed the research and wrote the paper; W.V.R., B.V.R., L.V., A.V.N., K.S. and J.-B.M. performed the analysis; A.W., J.M., J.v.V., D.v.D., J.B., F.T. and N.T. contributed data; A.V.N., K.S., J.-B.M., A.W., J.M., J.v.V. and F.M. read and commented on the paper. Competing interests The authors declare no competing interests. Additional information Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s43247-023-01050-7. Correspondence and requests for materials should be addressed to Ward Van Roy. Peer review information Communications Earth & Environment thanks the anonymous reviewers for their contribution to the peer review of this work. Primary handling editor: Martina Grecequet. A peer review ?le is available. 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