Blue marlin in the Atlantic are mainly landed as bycatch in longline fisheries for tuna and swordfish. While longlining is unlikely to have habitat impacts, it can have a bycatch of highly vulnerable species such as sharks, turtles, and seabirds.Monitoring and reporting of bycatch in fisheries managed by ICCAT is poor. Most data comes from scientific observers on vessels. Scientific recommendations are that 20% of a fishery should be observed for accurate data. ICCAT only requires coverage of 5%, increasing to 10% in 2022. Many fleets are not reaching this level. This makes it difficult to assess the impact of these fisheries on vulnerable species.There is a bycatch of loggerhead, leatherback and olive ridley turtles in longline and purse seine fisheries. According to the IUCN Red List, loggerhead turtles are endangered in the north east Atlantic and leatherbacks are endangered in the north west Atlantic and critically endangered in the southwest Atlantic. Observer data for 2020 indicates 20 dead discards of turtles, 1,308 live discards and 20 discards of unknown status. Given the poor observer coverage, this is likely to be an underestimate of the total catch. Post-release mortality is 1-4%. Longliners are required to safely unhook and release alive turtles, and purse seiners must avoid encircling them. Other scientifically recommended mitigation measures, such as using finfish bait and large circle hooks, are not mandated.Albatrosses and large petrels are amongst the most threatened groups of birds in the world, due in a large part to the impacts of bycatch in longline fisheries. In the Atlantic Ocean, bycatch of seabirds is most problematic in waters south of 25°S, which coincides with the greatest densities of albatrosses and large petrels. Observer data for 2020 indicates 195 dead discards of seabirds, 21 live discards and 2 discards of unknown status. Species recorded included the wandering albatross, the endangered sooty albatross, and the black-browed albatross. Given the poor observer coverage, this is likely to be an underestimate of the total catch. A recent assessment estimated that approximately 30,000-40,000 seabirds were killed by longlining in the Southern Hemisphere (including south Atlantic) between 2012 and 2016. The required mitigation measures do not follow recommended best practice by ACAP (the Agreement on the Conservation of Albatrosses and Petrels). ICCAT requires one or more measures from a set list of options, including weighted hooks, bird scaring lines and night setting, depending on location and target species. ACAP recommends the simultaneous use of all three, or hook-shielding or underwater bait setting devices. In the Mediterranean, all these mitigation measures are voluntary.Sharks are both bycaught and targeted in longline fisheries in the Atlantic. Bycatch species include the critically endangered scalloped hammerhead, silky shark, and the bigeye thresher, which is endangered in Europe and the Mediterranean. Observer data for 2020 indicates 1,098 dead discards of sharks and 1,109 live discards. Given the poor observer coverage, this is likely to be an underestimate of the total catch. There are some mitigation measures, such as restrictions on finning, but no gear-specific measures. This is in spite of repeated recommendations from the scientific committee to use circle hooks, which have been shown to increase survival of shortfin mako, blue marlin and swordfish if accidentally caught. Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako, which is heavily overfished, can be caught and retained. However, measures are came into force in 2022 to end overfishing of this species.There are no specific management measures to protect marine mammals, including cetaceans. ICCAT has not prioritised collecting data on mammal bycatch to date. More needs to be done to understand and reduce the impact of ICCAT fisheries on marine mammals.
