Yellowfin tuna

Yellowfin tuna in the western and central Pacific Ocean is not overfished or subject to overfishing.The western and central Pacific Ocean (WCPO) yellowfin tuna stock is managed and assessed by the Western and Central Pacific Fisheries Commission (WCPFC). Fishing for this stock began in the 1950s and catches have steadily increased, peaking in 2021 at around 750,000 tonnes. The WCPO yellowfin tuna fishery is the second largest in the world after WCPO skipjack. The last stock assessment was carried out in 2023 using data up to 2021. The next stock assessment is expected in 2026.Spawning Biomass (SB) continuously declined until the mid-2000s, when it reached around 50% of unfished levels. It has stayed relatively stable since then. The average SB between 2018 – 2021 was 47% of unfished levels and 228% of the level consistent with Maximum Sustainable Yield (MSY). The management objective is to maintain the spawning biomass depletion ratio above the average of 2012–2015, which was 44%. There is also a limit reference point (LRP) of 20%. Below this level, the stock would be considered depleted. As the biomass is above the management target and SBMSY, it is not in an overfished state.Since 2015, fishing mortality (F) has sharply increased for juveniles. In 2015, it was 22% of MSY and in 2021 it had increased to 46%. However, it has stabilized for adults. The average F from 2017-2020 was 50% of MSY, an increase on the previous assessment which was 36%. As F is below FMSY, the stock is not subject to overfishing. All models in the assessment indicated that the stock was above SBMSY, and fishing mortality rates below FMSY, with 100% probability. Therefore, it is not overfished, nor subject to overfishing. Assuming fishing effort and catch levels stay at 2018-2021 levels, there is a zero probability of the stock falling below the LRP.There are some research needs to improve the assessment, including estimation of natural mortality rates using tagging data.

Some appropriate management measures are in place to control fishing activity. However, catches have increased to record levels. Regulations are insufficient to prevent them from increasing further and potentially exceeding sustainable limits.Tuna 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. It is important that commercial buyers choose tuna that has been caught by vessels that are well regulated by their flag state.This stock is managed and assessed by the Western and Central Pacific Fisheries Commission (WCPFC). Some stocks overlap with the Inter-American Tropical Tuna Commission (IATTC). 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. A significant proportion of West Pacific skipjack and yellowfin tuna is caught within the waters of the Parties to the Nauru Agreement (PNA). These South Pacific island nations have incorporated additional management measures, and pushed for improvements in the wider management of these stocks.The WCPFC has not yet set a target size for the yellowfin stock, although work is underway to achieve this. In the interim, for 2022-2024 there is a harvest strategy that aims to maintain the stock at 2012-2015 average levels, which is 44% of unfished biomass. The 2018-2021 spawning biomass was 47% of unfished levels. There is no explicit target for fishing mortality.There is no Total Allowable Catch. Instead, management is mainly aimed at limiting fishing effort by purse seiners, which are responsible for around 53% of the yellowfin catch. Each country has set their own catch or effort limits for purse seining within their own waters. On the high seas in the tropics (between 20 degrees N and S), each country is allowed to fish for a set number of days. Fishing effort (in days) in the areas outside of this should not increase. Purse seiners must retain and land all bigeye, skipjack, and yellowfin tuna. This is intended to incentivise reductions in bycatch of juvenile fish. Yellowfin catches by other fishing gears are frozen to 2004 levels.This has not prevented catches from increasing. The catch in 2004 was 600,000t. The 2016-2020 average is 700,000t with 2021 seeing the highest catch on record at 754,442t. Management is not, therefore, controlling fishing pressure on the stock. WCPFC has also noted that further increases in fishing mortality are likely to impact other stocks and species due to multispecies and gear interactions.There are also restrictions on the use of drifting fish aggregation devices (dFADs) - floating objects which purse seiners use to attract tuna and increase catches. Each purse seine vessel is limited to 350 dFADs at a time. FADs are banned from July-September, with an additional 2-month closure in parts of the southwest Pacific islands. VMS polling frequency increases to every 30 minutes during the FAD closure.Additional measures for all newly deployed FADs came into place in January 2024. This includes prohibiting mesh netting on any part of a FAD, and only allowing non-entangling materials and designs for raft covers and subsurface structures. Decisions on implementation of biodegradable FAD requirements are scheduled for no later than 2026. Currently, biodegradable and non-plastic materials are encouraged but not required. There is uncertainty about the level of compliance and effectiveness of these new regulations due to varying observer coverage and the recent date of implantation.Observers, to verify catch and bycatch, are required on 100% of purse seiners between 20 degrees N and S, but are low for other areas and gear types at just 5%. These observer levels have not been routinely met, peaking in 2018 and 2019 at 90% for purse seine and 6% for longline. In 2021 observer coverage fell to below 10% and 4% for purse seine and longline fisheries due to the impacts of the COVID-19 pandemic and lonely slightly improved in 2022. Scientific recommendations are for 20%.To help address illegal, unreported, and unregulated (IUU) fishing, the WCPFC maintains an IUU Vessel List, prohibits transhipments at sea between purse seiners (some exemptions apply) and requires all other transhipments to be documented and 100% observed as part of the regional observer programme. In 2017 a Compliance Monitoring Scheme was introduced to assess and improve compliance with obligations, and penalise non-compliance.

Some of the yellowfin tuna catches in the western and central Pacific Ocean are by longlining. While longlining is unlikely to have habitat impacts, it can have a bycatch of highly vulnerable and endangered species, including sharks, turtles, and seabirds.Around 12% of western and central Pacific Ocean (WCPO) yellowfin catches are by longlining (87,000t in 2022). The longline catch has increased by more than 15% from 2021 levels. A number of Endangered and Critically Endangered species are caught as bycatch in WCPO longline fisheries.Data on bycatch in longline fisheries is poor, partly because there are not enough scientific observers on vessels. Observer coverage is only required to be 5%, and recommendations are for at least 20%. WCPFC reported that the 5% target is not currently being achieved, and the situation has been exacerbated by ongoing Covid impacts. In 2022, coverage was 4%. WCPFC scientists advise that observer coverage has been particularly poor in the northwest Pacific, and for all WCPFC bycatch data, trends are more reliable than magnitudes. There are regulations for sharks and rays, turtles, seabirds and cetaceans. Most highlight the need for better data. Some bycatch mitigation measures are in place, but they often don't follow scientific recommendations for best practice, and their effectiveness has not been evaluated.In 2020, an estimated 1.7 million sharks were caught as bycatch or had an interaction with WCPO fisheries. Of these, around 34,000 individuals were caught in FAD-free purse seines, 60,000 in FAD-associated purse seines, and 1.1 million by longlining. A proportion of these will have been released alive, however. Observer data indicates that there were 5,500 purse seine mortalities and 3,150 longline mortalities in 2020. As just 5% of the longline fleet is observed, this is a significant underestimate of total mortality. Bycatch species include bigeye thresher, shortfin mako, and silky. Of greatest concern is oceanic whitetip shark, which is in a severely overfished state and critically endangered. In the WCPO, it is at just 4% of unfished levels, although fishing pressure has been reduced and there are some signs of recovery. The greatest impact on this species is bycatch from longline fisheries, with lesser impacts from purse seining. Further catch mitigation and improved handling and release practices are required. Mobulid rays are also bycaught, but there is very little data on these species.The status of silky and oceanic whitetip sharks is of concern as assessments have shown that these stocks are subject to overfishing and, in the case of oceanic whitetip, is severely overfished.There are some mitigation measures, including restrictions on finning, a ban on landing silkies and oceanic whitetips; and restrictions on the use of shark lines (which increase bycatch in longlining). The effectiveness of these measures are difficult to evaluate owing to lack of data. As of 2014, shark management plans are required where sharks are being targeted, although few countries have developed them.The five marine turtle species in the WCPFC Convention Area (green, hawksbill, leatherback, loggerhead and olive ridley) are vulnerable, endangered, or critically endangered. A 2023 review estimated that turtles represented 0.1% of WCPFC longline catch from 2003-2019, and around 13,000 individuals in 2021. Around 15% of turtle catches were loggerhead, 52% were olive ridley and 13% green. NOAA lists the North Pacific loggerhead population as endangered, with fisheries bycatch being the primary threat. There are some mitigation measures, including requirements for safe handling and release. Shallow-set swordfish longliners must use circle hooks and whole finfish bait (with some exemptions), but this covers less than 1% of WCPO longline effort, even though approximately 20% of the WCPO longline effort consists of shallow sets. The remaining 80% of longlining, which is deeper-set, has no mitigation requirements. Turtle interaction rates are thought to be higher in shallow-set longlines, but mortality rates are higher in deeper sets because sea turtles have a higher probability of asphyxiation.Seabird bycatch is also a concern. Albatrosses and petrels are attracted to the baited hooks on longlines. Data on seabird bycatch is not good enough to fully assess the impact of longlining in the WCPO, owing to the low observer coverage. Even the data that is recorded is thought to be a significant underestimate, due to lost, undetected bycatch. However, in the WCPO, modelling has estimated that between 13,000 and 19,000 seabirds were killed annually in longline and purse seine fisheries from 2015 to 2018. Two thirds of the mortalities were by longline fisheries north of 20 degrees N. Two thirds of the mortalities were by longline fisheries north of 20 degrees N, one quarter by longline fisheries south of 30 degrees S, and negligible amounts from purse seining. A small area east of Tasmania and south of 40 degrees S is estimated to account for around 60% of the longline seabird bycatch south of 30 degrees S and 15% of the total. Of critical concern is Antipodean wandering albatross, which is expanding its foraging range into tuna fishery areas and has experienced a high and sustained rate of decline - it is now in New Zealand's "Nationally Critical" conservation status category.Countries are expected to implement the International Plan of Action for Reducing Incidental Catches of Seabirds in Longline Fisheries (IPOA-Seabirds) and report back on this. The required longline mitigation measures do not follow recommended best practice by ACAP (the Agreement on the Conservation of Albatrosses and Petrels). WCPFC requires one or two measures (depending on location) from a set list of options, including weighted hooks, bird scaring lines and night setting. ACAP recommends the simultaneous use of all three, or hook-shielding or underwater bait setting devices. Further research is being done on hook shielding devices, and countries are encouraged to develop and refine measures to mitigate seabird bycatch, including safe release of seabirds captured alive. Scientific advice is to increase observer coverage and ensure compliance with existing regulations.Interactions between marine mammals and longliners have been recorded, but data is very poor. They can be attracted by the fish caught on the line. Species have included false killer whales and other cetaceans. A 2023 review estimated that mammals represented 0.01% of WCPFC longline catch from 2003-2019, and around 1,500 individuals in 2021.

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