Skipjack tuna

Skipjack tuna in the western and central Pacific Ocean is not overfished or subject to overfishing.The western and central Pacific Ocean (WCPO) skipjack tuna stock is the largest tuna fishery in the world, accounting for approximately 37% of worldwide tuna landings. Catches of this stock increased steadily from 1970 onwards, reaching a record of over 2 million tonnes in 2019.The WCPO skipjack tuna fishery is managed and assessed by the Western and Central Pacific Fisheries Commission (WCPFC). The last stock assessment was carried out in 2022 using data up to 2021. The next stock assessment is expected in 2025.Spawning Biomass (SB) has declined from about 90% of unfished levels in 1970 to 51% in 2021. This is an improvement on the 2018 estimate of 44%. It is above the Target Reference Point of 40%, and well above the Limit Reference Point of 20%. Therefore, the stock is not in an overfished state.Fishing Mortality (F) has increased since the 1970s, peaking in 2018 at 45% of levels associated with Maximum Sustainable Yield (MSY). It has since declined slightly to 32%. As F is below MSY, the stock is not subject to overfishing.Trends in spawning biomass vary by region, and there is a higher depletion rate in equatorial areas. However, projections indicate that if the 2018-2021 average catch and effort levels are maintained, there is zero probability of the stock breaching its limit reference point.

Some appropriate management measures are in place to control fishing activity. However, catches have increased to record levels. Regulations have been insufficient to prevent them from increasing further and 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 Western and Central Pacific Ocean (WCPO) skipjack stock supports the largest tuna fishery in the world, accounting for approximately one third of worldwide tuna landings. It is not overfished or subject to overfishing, although fishing mortality is continuously increasing. The main management measure is now a Harvest Control Rule (HCR), which came into force in 2023.The HCR sets out targets to keep the stock at certain levels, and rules for deciding limits on catch and fishing effort. It aims to keep the stock size between 40% and 56% of unfished levels. The stock should also be above the point of reproductive impairment - 20% of unfished levels - with at least 80% probability. If the stock falls below 40%, fishing mortality must be reduced. Above 56%, it can be increased. Catch and effort limits will be set for 3 year periods. Changes are limited to up to 10% from one period to the next, to keep the fishery stable. Limits have not yet been published for 2023, so it is too early to tell what impact this will have on the fishery.To date, management of the tropical tuna fisheries (skipjack, yellowfin and bigeye) has primarily been by controlling the purse seine fishery. This method is responsible for around 80% of skipjack catches. The focus is on the main fishing grounds, between 20 degrees North and South, which is where fishing has the highest impact on the skipjack stock. In this area:Each country is allowed to fish for a set number of days. Fishing effort (in days) should not be displaced to other areas.Purse seiners must retain and land all bigeye, skipjack, and yellowfin tuna. This is intended to incentivise reductions in bycatch of juvenile fish.Fish Aggregating Devices (FADs) - floating objects which purse seiners use to attract tuna and increase catches - are banned from July-September. There is an additional 2-month closure in parts of the southwest Pacific islands.Vessel Monitoring System (VMS) polling, which tracks vessels using satellites, increases to every 30 minutes during the FAD closure.Observers, to verify catch and bycatch, must be on 100% of large purse seiners.In addition:Purse seine vessels are limited to 350 drifting FADs each.Each country has set its own catch or effort limits for purse seining within their own waters.Skipjack catches by other fishing gears are frozen to 2004 levels.This has not prevented catches from increasing. The catch in 2004 was 1.36 million tonnes. The 2017-2021 average is 1.75 million tonnes, with 2019 seeing the highest catch on record at over 2 million tonnes. The stock assessment indicates that fishing mortality is continuously increasing. Management has not, therefore, controlled fishing pressure on the stock.Observer coverage for other gears, including small purse seiners, and in other areas is low, at just 5%. There is not enough data to be sure that countries are complying with the management measures.To help address IUU, 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 skipjack 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 80% of western and central Pacific Ocean (WCPO) yellowfin catches (around 1.4 million t in 2020). Around half the purse seine catches 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 2.1% 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. At the scale of this fishery, 2.4% bycatch is a significant quantity.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. It has been estimated that across the Indian, Atlantic and Pacific Oceans around 100,000 FADs are deployed, and 7-22% of them may become stranded. 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 designs 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 is required for purse seine vessels fishing for tropical tunas between 20 degrees North and 20 degrees South. Outside of this and for other gears, observer coverage is poor at just 5%. 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. The most common species are blue shark and silky shark, but there is also sizable bycatch of shortfin mako, bigeye thresher, and oceanic whitetip. Of greatest concern are silky shark and oceanic whitetip, as both are subject to overfishing. Oceanic whitetip is also in a severely overfished state and critically endangered. 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%). Mobulid rays are also bycaught, but there is very little data on these species.There are some mitigation measures. Shark finning is banned. From 2024, between 20 degrees north and south, vessels cannot use shark lines or wire leaders, which increase bycatch in longlining. Countries targeting sharks must have shark management plans, although few countries have developed them. Sharks should be safely handled and released alive if unwanted bycatch. Landing silkies and oceanic whitetips is prohibited. The effectiveness of these measures are difficult to evaluate owing to lack of data.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. Data from the Pacific Islands indicates an average of 1,900 purse seine bycatch incidents from 2015-2019. Observer data for the whole WCPFC area indicates 27 deaths from purse seining in 2020. 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.