Following the tuna trail: Contrasting global catch estimates from FAO and RFMOs

This study compares annual catch statistics from the Global Tuna Atlas (GTA) and FAO FishStat (FS) marine capture datasets, with a focus on tuna and tuna-like species. The analysis first describes the differences between both dataset structures, then applies a harmonized mapping and filtering procedure to enable consistent inter-comparison. At the global scale, total catches from both datasets are highly consistent (differences < 1%), yet this apparent agreement conceals substantial variations at finer levels, particularly by species and fishing fleet. These discrepancies often compensate each other across years, producing an illusion of equivalence in aggregated time series. A regional focus on the Indian Ocean Tuna Commission (IOTC) management area confirms this pattern: while temporal trends are parallel overall, differences emerge for some species such as bigeye tuna and Albacore, often linked to specific fleets. In recent years (post-2014), several species show nearly identical values in both datasets, reflecting cases where one source adopts figures from the other when deemed more reliable. However, differences persist for certain taxa and, in some cases, where the underlying data flows or integration processes differ between the two datasets. This analysis highlights both the complementarity and the limitations of GTA and FS: GTA provides detailed fishing gear and fishing mode, while FS offers finer spatial resolution and broader taxonomic coverage. Understanding these structural and procedural differences is essential for ensuring the comparability and reproducibility of global fisheries statistics.