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The document provides an overview of the consolidated knowledge about fisheries catching black marlin (Istiompax indica) in the Indian Ocean since the early 1950s based on a range of data sets collected by the Contracting Parties and Cooperating Non-Contracting Parties (CPCs) of the IOTC and curated by the IOTC Secretariat. The available fisheries statistics show a major decline in black marlin catch since the mid-2010s after an increasing trend over several decades. While catches were mostly reported for industrial longline fisheries prior to the 1980s, the contribution of coastal fisheries has steadily increased since then to represent more than 63% of the total black marlin catch in 2021. The recent decline in total catch is explained by the decrease in catch from large-scale longline fisheries which started since 2008 combined with the reduction in catches from small longline fisheries from Sri Lanka and India. Information available on discarding practices of black marlin in industrial fisheries indicates that discard levels are small in longline fisheries while black marlins are more often discarded in large-scale purse seine fisheries, although in small quantities. Discarding in coastal fisheries interacting with the species is poorly known but considered to be negligible. Information available on the spatial distribution of catch and effort has substantially improved over the last decade and shows that black marlins are mostly caught in the northwestern part of the Indian Ocean, with important catches reported along the coasts of the Arabian Sea, India, and Sri Lanka. The reporting of size-frequency data has slightly improved over the last decade but remains very limited for most artisanal and industrial fisheries.
