A study published in Science Advances has identified the owners and flags of all globally used refrigerated cargo vessels (reefers), which are used as mobile ports for fishing boats and are a weakness in the traceability of the seafood value chain. The research found that 324 owners are responsible for all transshipment of fish worldwide, with a significant contribution from China, Russia, and Greece. The study identifies 569 reefers currently in use and their 324 beneficial owners, with 10 owners accounting for nearly a quarter of all transshipment events. The data from the study is freely accessible and can be used by NGOs, insurance companies, and financial actors to promote sustainable behaviors at sea.