Blue marlin

Atlantic blue marlin has been overfished for the last 10-15 years, and the most recent stock assessment in 2024 indicates that the stock is still in an overfished state, but is no longer subject to overfishing.Atlantic blue marlin stocks are managed by the International Commission for the Conservation of Atlantic Tuna (ICCAT). This stock has been fished since the late 1950s, with catches peaking at 9,000t in the early 1960s and dropping to around 2,000t in the late 1970s. After rising to over 5,700 tonnes in 1997, catches have declined again to around 2,000t in 2023.The most recent stock assessment is from 2024, using data up to 2022. The assessment shows that the spawning stock biomass (SSB) has continuously declined since 1960, dropping below levels associated with Maximum Sustainable Yield (SSBMSY) in the 1990s. SSB in 2022 was estimated to be 67% (B2022/Bmsy = 0.67) of the target level (SSBMSY). The stock is therefore in an overfished state.Fishing pressure (F) increased from the late 1970s, exceeding target levels (FMSY) since around 1990. It has declined since the early 2000s. Fishing pressure is now below FMSY, in 2022 F was 8% below FMSY (F2022/Fmsy = 0.91). Therefore, the stock is not subject to overfishing.Catches are likely to be underestimated owing to significant unreported catches, particularly in artisanal fisheries. There is also a lack of reporting on live releases or dead discards.Blue marlin are listed globally as Vulnerable by the International Union for the Conservation of Nature (IUCN), and Endangered in the Gulf of Mexico.

A rebuilding plan came into force for this stock in 2020. It follows scientific advice, but it is too early to tell if it will be effective. Catches are likely to be underestimated, and observer coverage is low, so these fisheries are not well monitored.Tuna, marlin, and swordfish are highly migratory species, found on the high seas and in numerous countries' waters. This makes harmonised and effective management challenging. Regional Fisheries Management Organisations (RFMOs) are responsible for monitoring and managing these stocks on behalf of the countries that access them. However, the degree to which management is implemented, monitored and enforced by each country varies significantly.This stock is managed and assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Atlantic blue marlin has been overfished and subject to overfishing since the 1990s. The main management measures are a catch limit (Total Allowable Catch, TAC) and a rebuilding plan.The blue marlin TAC for 2013-2019 was 2,000 t, with individual catch limits assigned to each country. However, catches exceeded this limit in 2016 and 2017, which prevented the stock from recovering. Scientific advice from the 2024 stock assessment was to lower or maintain to the current landings limit of 1,670t until the increased biomass trend seen in the 2024 assessment is confirmed at the next assessment. A rebuilding programme was agreed in 2019, aiming to end overfishing of blue marlin and rebuild the stock. An annual catch limit of 1,670t, began in 2020 and has continued to the most recent assessment. Catch in 2022 and 2023 was 1,789t and 2,068t, respectfully, these both exceeded the annual catch limit.Additionally, catches are probably underestimated owing to poor reporting from some artisanal fisheries and a lack of data on discards. This is of serious concern for future assessments, prevents assessment of the effectiveness of current regulations, and reduces the likelihood that any additional management measures will work.Under the rebuilding plan, longliners and purse seiners can only land dead marlins. If they are alive at the point of being hauled in, they should be released in a way that maximises survival. This is in line with scientific advice to reduce fishing mortality and minimise the chance of exceeding TACs. While there have been studies and data collected on the live release of blue marlin, there is not enough information on the proportion of fish being released alive to evaluate the effectiveness of this measure.Around 70%-80% of marlin catches are by longlining. To help reduce marlin bycatch, circle hooks can be used on longliners. However, most countries have not implemented this as a requirement. Marlin bycatch also happens around Fish Aggregating Devices. Over the last 20 years, Antillean artisanal fleets have increased the use of Moored Fish Aggregating Devices (MFADs) to capture pelagic fish. Catches of blue marlin caught around MFADs are known to be significant and increasing in some areas, however reports to ICCAT on these catches are incomplete.This fishery is not well monitored. Observer coverage increased from 5% to 10% in 2022. Many fleets might not have reached this level, although some are at 100%. Scientific recommendations are for at least 20% for accurate reporting of bycatch. Vessel Monitoring Systems are required for all vessels over 24m, which means smaller vessels are less well monitored.In terms of enforcement and compliance with management measures: in 2016 ICCAT passed measures to strengthen and streamline its compliance assessment process and to develop a scheme of responses to non-compliance. There is also a list of vessels authorised to fish for tuna and tuna-like species in the ICCAT area, and a list of vessels caught carrying out Illegal, Unreported or Unregulated activities. At-sea transhipment is prohibited unless pre-authorised and the vessel has an observer on board.

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.