Pacific bluefin tuna

There is concern for the biomass and fishing pressure of Pacific bluefin tuna. The stock has been gradually recovering and rebuilding targets continue to be met ahead of schedule, but the stock assessment still lacks formal reference points.Route 2 (data limited) scoring has been applied to this rating owing to the lack of reference points for biomass and fishing pressure. Pacific bluefin tuna is considered to have medium resilience to fishing.Pacific bluefin tuna is assessed by the International Scientific Committee for Tuna and Tuna-like species in the North Pacific (ISC). It has a single Pacific-wide stock managed by both the Western and Central Pacific Fisheries Commission (WCPFC) and the Inter-American Tropical Tuna Commission (IATTC). The last stock assessment was carried out in 2024 using data up to 2022. The next assessment is expected in 2026.This species has been fished since the early 1800s. Historical catch records are poor, but catches appear to have peaked before the 1940s at about 50,000t. After this, they fluctuated widely, and are now around 18,000t.Biomass, expressed as spawning stock biomass (SSB), declined steadily from approximately 150,000 t in the early 1960s to 12,600 t by the mid‑1980s. Following a brief period of improvement, SSB fell again to a historic low of 10,800 t in 2010, representing just 1.7% of estimated unfished levels. SSB has shown gradual recovery since then, increasing to 5.6% in 2018 and 10.2% in 2020.Although there is no formal reference point for determining stock status, the initial rebuilding target was to reach 6.3% of unfished biomass by 2024. This milestone was achieved in 2019, five years ahead of schedule. The subsequent management target, 20% of unfished levels by 2029, was also met early, with SSB estimated at 23.2% in 2022.The Marine Conservation Society considers 20% of unfished biomass to be equivalent to Blim. Below this level, and in line with common reference points used for tuna stocks, the stock would be considered outside safe biological limits. As SSB has now risen above this threshold, the stock is no longer assessed as being outside safe biological limits. However, it is still classified as overfished and therefore there is concern for biomass levels.Fishing mortality (F) is measured as spawning potential ratio (SPR) - the reproductive potential of fish at the current fishing pressure compared to an absence of any fishing. F was at 1% SPR from 2004-2009 and has since improved to 23.6% SPR for 2020 - 2022. To achieve a biomass of 20% of unfished levels, the corresponding F would also be 20% SPR. Therefore, fishing mortality is at a level that should allow the stock to increase above Blim. However, this is not the level of fishing pressure that would be associated with a long-term sustainable Maximum Sustainable Yield - that target has not been defined. It is often set at 30% or 40% for other tuna stocks. It is therefore not possible to know whether the stock is subject to overfishing, therefore there is concern for fishing pressure.There is not yet a formally adopted target for the long term but maintaining the stock at levels capable of producing maximum sustainable yield is considered as a potential target.

Management appears to be recovering Pacific bluefin tuna from historically low levels. However, the rebuilding plan is not precautionary as it is allowing catches to increase while the stock remains severely depleted.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.Pacific bluefin tuna (PBF) is a single Pacific-wide stock managed by the Western and Central Pacific Fisheries Commission (WCPFC) in the west, and the Inter-American Tropical Tuna Commission (IATTC) in the east. The impact of fisheries in the WCPFC convention area on PBF (83%) is far greater than that of fisheries in the IATTC area (17%), and so management measures by WCPFC are considered to be of greater importance. However, management must be comparable and properly implemented across the entire range of the stock in order for it to be effective. The IATTC and WCPFC endeavour to work together to promote compatibility between their respective conservation and management measures across the Pacific, but this is not always achieved.PBF has been badly managed in the past, with a lack of regulation and enforcement across its range. Contributing to this has been its extremely high market value, adding incentive for Illegal, Unreported and Unregulated (IUU) fisheries. In 2010 the stock had dropped to just 1.7% of its unfished levels. A Northern Committee working group comprising IATTC, WCPFC and others was established in 2016 to support joint working on Pacific bluefin tuna. The main management measures are a rebuilding plan and harvest strategy.The rebuilding plan, started in 2015, has an initial goal of rebuilding the spawning biomass (SB) to the historical median, 40,994t, by 2024 with at least 60% probability. This would take the SB to 6.4% of unfished levels. This was reached in 2019, ahead of schedule. A second rebuilding target was adopted in 2018: to reach 20% of unfished levels within 10 years of reaching the initial target (i.e. by 2029) with at least 60% probability. Current management measures are on track to achieve and potentially exceed this target. Management therefore appears to be effectively rebuilding the stock.There is also a harvest strategy in place for the stock. If the probability of achieving the rebuilding target drops to less than 60%, catches of small fish (below 30kg) should be reduced. If the probability is above 75%, overall catches are allowed to increase (with some restrictions). This potential for increasing catches, even when the stock is in a highly depleted state, is concerning. In the 2020 stock assessment, recruitment for 2017 and 2018 was estimated to be the lowest since early 1990s. Scientific advice is that future recruitments may remain low until there is sufficient recovery in spawning biomass. Therefore, scientists have urged the commissions to take a precautionary approach to the management of Pacific Bluefin tuna. Management does not appear to be taking a precautionary approach.There are catch limits, set differently by the two RFMOs.In the northern WCPFC area (north of 20 degrees N), fishing effort is frozen to each fleet's 2002-2004 average. Countries appear to be staying within those limits. Catch for the whole area is frozen to 2002-2004 levels for large bluefin (over 30kg). The catch limits up to 2021 equated to around 14,000t. For 2022, the limit was increased by 15% for large bluefin (catches can now be 115% of the 2002-2004 average).In the IATTC area, total catch limits are set for 2-year periods. The 2021-2022 limit was 7,295t, increasing to 7,990t for 23-24. IATTC report 40% catch reductions in their area since 2012 through resolutions and voluntary measures. IATTC's scientific committee has recommended that WCPFC do more to limit catches of adult bluefin.According to the International Scientific Committee for Tuna and Tuna-like species in the North Pacific (ISC), total PBF catches in 2021 were 14,766t. This is above the 2017-2021 average (13,000t). As noted above, increasing catch limits at this early stage of recovery is not precautionary.Both RFMOs require reductions in catches of 'small' PBF (below 30kg). In the WCPFC area the limit is 50% of 2002-2004 average levels. In the IATTC area the limit is 50% of the total catch. Juvenile Pacific bluefin tuna can weigh up to 85kg, so this does not protect juveniles.Monitoring of the fisheries is not high enough for some fleets. Both RFMOs have 100% observer coverage on large purse seiners but only 5% on large longliners. A minimum of 20% is recommended for accurate data. In addition, data recorded by longliners in the IATTC area is considered inadequate for scientific purposes and minimum data standards must be identified and introduced.To help address illegal, unregulated and unreported fishing, WCPFC and IATTC maintain an IUU Vessel List; a register of authorised large longliners; and prohibit transhipments at sea for large purse seiners, and most other transhipments must be documented and observed as part of the regional observer programme. Countries are required to report annually on monitoring, control and compliance of management measures. There is also a joint WCPFC-IATTC catch documentation scheme (CDS) for PBF.

Some Pacific bluefin tuna are caught by longline. While longlining is unlikely to have habitat impacts, it can have a bycatch of highly vulnerable and endangered species, including sharks, turtles, and seabirds.Approximately half of the Pacific bluefin tuna catch is taken by purse‑seine fleets, with the remainder caught mainly by gillnets and trolling fisheries (31%), and longline fisheries accounting for around 19% of catches. Overall, about 70% of Pacific bluefin tuna catches occur in the western Pacific Ocean, with the remainder spread across the wider Pacific. While longlining represents a smaller proportion of total catch than purse seining, longline fisheries targeting tropical tunas are associated with substantial bycatch risks, the assessment of which is constrained by very poor monitoring and limited data availability.Observer coverage in Pacific longline fisheries is extremely low, with only 5% coverage required, despite scientific recommendations that at least 20% is necessary to generate reliable bycatch estimates. The 5% target is frequently not met: in the WCPO, observer coverage fell to around 4% in 2022, with especially poor coverage reported in the northwest Pacific. As a result, reported bycatch figures are considered significant underestimates, and trends are more reliable than absolute mortality estimates. Although regulations exist for sharks, rays, sea turtles, seabirds and cetaceans, most explicitly acknowledge the need for better data, and the effectiveness of mitigation measures has not been robustly evaluated.Shark bycatch represents one of the most serious concerns. In the WCPO in 2020, an estimated 1.6-1.7 million sharks were caught as bycatch or interacted with fisheries, with approximately 1.1 million taken by longline fisheries. Observer data recorded around 3,150 longline shark mortalities, but this figure reflects only a small fraction of total fishing effort. Bycatch species across both regions include bigeye thresher, shortfin mako and silky sharks, as well as critically endangered oceanic whitetip and scalloped hammerhead sharks, and the endangered pelagic thresher. Oceanic whitetip sharks are of particular concern, as the stock is assessed at around 4% of unfished levels in the WCPO, with longline bycatch identified as the primary driver of decline. Some mitigation measures are in place, including finning restrictions, bans on landing silky sharks and oceanic whitetips, and limits on shark lines, but their effectiveness remains unclear due to data limitations. Mobulid rays are also bycaught, though information on impacts is extremely limited.Seabird bycatch is another major issue, particularly for albatrosses and large petrels, which are attracted to baited longline hooks. Available data are insufficient to fully assess impacts, but modelling suggests that 13,000-19,000 seabirds were killed annually in western Pacific tuna fisheries between 2015 and 2018, with longline fisheries responsible for the majority of mortality. Of particular concern is the Antipodean wandering albatross, which has expanded its foraging range into tuna fishing grounds and is now classified as Nationally Critical in New Zealand. Required mitigation measures do not align with ACAP best practice, as WCPFC permits the use of only one or two mitigation tools (e.g. bird‑scaring lines, weighted hooks or night setting), while ACAP recommends using all three simultaneously or alternative hook‑shielding or underwater bait‑setting devices.Marine turtles are also captured in Pacific longline fisheries. All five species present in the WCPO (green, hawksbill, leatherback, loggerhead and olive ridley) are listed as threatened, with the Eastern Pacific leatherback turtle critically endangered and at risk of extinction, primarily due to longline and gillnet interactions. A 2023 review estimated that turtles represented 0.1% of WCPFC longline catch, equating to around 13,000 individuals in 2021. Interaction rates are higher in shallow‑set longlines, while mortality rates are higher in deeper‑set fisheries due to increased risk of asphyxiation. Mitigation measures include safe handling and release requirements, and limited use of circle hooks and finfish bait in shallow‑set swordfish fisheries; however, these measures apply to less than 1% of WCPO longline effort, leaving the majority of the fishery without effective mitigation.Interactions with marine mammals have also been recorded, including false killer whales and other cetaceans, but data are extremely limited. A recent review estimated that marine mammals represented around 0.01% of longline catch in the WCPO, or approximately 1,500 individuals in 2021, though true levels of interaction remain uncertain.Overall, Pacific bluefin tuna longlining in the Pacific Ocean is characterised by, data gaps, and high bycatch risk, particularly for sharks, seabirds and threatened marine megafauna. While some mitigation measures exist, they fall short of scientific best‑practice recommendations, are applied inconsistently, and cannot currently be evaluated for effectiveness due to inadequate monitoring and enforcement.