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.

Most of the yellowfin tuna catches in the western and central Pacific Ocean are by purse seining. This method is associated with bycatch of species such as sharks, turtles and marine mammals.Purse seining accounts for around 53% of western and central Pacific Ocean (WCPO) yellowfin catches (around 370,000t in 2022). Some purse seine catches (20%) are from Fish Aggregating Devices (FADs) and the rest is on free schooling tuna, but it is not always possible to verify which catches are from which method.Purse seining is associated with bycatch of species such as sharks, turtles and marine mammals, although less so than longlining. Bycatch is higher when FADs are used. FADs are floating objects that tuna and other species tend to aggregate around. It is estimated that 1.1% of the total catch (by weight) in FAD fisheries in the western Pacific is non-target species, as opposed to 0.3% in free-schooling fisheries.FADs can include hanging elements such as ropes and nets, which can entangle vulnerable species. FADs can also become lost at sea, continuing to ghost fish and be a source of marine debris. Some mitigation measures are in place. The Western and Central Pacific Fisheries Commission (WCPFC) limits how many FADs each vessel can use, and bans them for part of the year. Countries must use non-entangling FADs and biodegradable are encouraged. Implementation of this is slow: a 2020 assessment indicated that 65-90% of FADs have nets attached, which are the main cause of entanglement.To help gather data on catch and bycatch, 100% observer coverage has required for purse seine vessels fishing for tropical tunas between 20 degrees North and 20 degrees South since 2010. Outside of this and for other gears, observer coverage is poor at just 5%. In practice, these covered levels are not regularly met though have been increasing. Purse seine coverage peaked in 2018 at just over 90%, and longline in 2019 at just under 6%, coverage rates have not yet fully recovered since the impacts of the COVID-19 pandemic. Scientific recommendations are for a minimum of 20% for useful data.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 1.6 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. These are thought to be an underestimate. 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. Redistribution of purse seine effort from FADs to free schools has resulted in substantial reductions in estimated catches of silky shark (by 83%) and oceanic whitetip shark (by 57%). 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.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, and WCPFC does not have enough data to assess the threat posed by fisheries. Observer data indicates 0 deaths from purse seining in 2020. There are some mitigation measures, including requirements for safe handling and release.Cetaceans are vulnerable to being encircled by purse seine nets because tuna tends to form schools around them. They are also attracted to the same prey as tuna. These interactions are not well recorded and the scale of impact by purse seining is unclear, but likely to be underestimated. Species recorded include false killer whales, Bryde's whales, and sei whales. Around 80% of interactions result in the animal being released alive. It is illegal to deliberately set a purse seine net around tuna if a cetacean is also present. If one is accidentally encircled, it must be safely released and recorded.The fishery is not considered to be a threat to seabirds.FADs are also of concern due to the unknown impacts such gear might have on other tuna and fish species in relation to species composition of schools, migratory patterns, growth rates and predation rates. Juvenile and bigeye tuna are caught by purse seining, and scientific recommendations are for these impacts to be reduced to protect the stocks.