Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Purse seine (FAD & Free School)
Capture area — Pacific, Eastern Central (FAO 77), South, East (FAO 87) and West (FAO 81)
Stock area — Eastern Pacific
Stock detail — All Areas
Picture of Tuna, skipjack

Sustainability rating four info

Sustainability overview

Updated: November 2020

East Pacific skipjack is not well understood, and management cannot be truly science-based until there are better stock assessments available. While the stock is not thought to be overfished or subject to overfishing, fishing mortality is increasing and there are no catch limits. The primary measure has been limits on the purse seine fishery (responsible for 99% of catches). These limits include closed areas and seasons, and limits on the number of Fish Aggregating Devices (FADs) that can be used. The FAD limits are considered to be too high and don’t restrict the fishery enough. The capacity (number and size of vessels) of the fleet was supposed to have been frozen to 2002 levels, but has since increased. 99% of the skipjack landings in the Eastern Pacific Ocean (EPO) are from purse seining: 70% on floating objects including Fish Aggregation Devices (FADs), and 29% on free schooling fish. Purse seining is associated with bycatch of species such as sharks, turtles and marine mammals, although less so than longlining. Whilst bycatch may comprise a small proportion of the total catch, the high volume of tuna that is caught means that it can still be significant for these vulnerable species. Bycatch is higher where Fish Aggregation Devices are being used. Poorly-designed FADs can entangle vulnerable species, and can also become lost at sea, continuing to ghost fish and be a source of marine debris. Some management is in place, but better data is needed to understand and control impacts.

Commercial buyers should establish what measures the flag state and fleet relating to their source is taking to improve the management of FADs and status of bycatch and other tuna species caught with skipjack. Large buyers should consider supporting such improvements. MCS also advocates specifying the need for supplying vessels, in particular purse seiners, to register on the ISSF Proactive Vessel Register. There are some Marine Stewardship Council (MSC) certified fleets within this area which represent the best option. There are also some Fisheries Improvement Projects (FIPs) for purse seine fleets operating in this area which are making good progress to address some key environmental issues and aim to achieve MSC certification. Further information about these FIPs is available from fisheryprogress.org.

Biology

Tuna belong to the family Scombridae. They are large, oceanic fish and are seasonally migratory, some making trans-oceanic journeys. Skipjack tuna are found throughout the world’s tropical and warm temperate waters. During the day they school on the surface (often with birds, drifting objects, sharks, whales etc.) but at night can descend to depths of 260m. Skipjack tuna are a very fast growing species, maturing at 2 to 3 years old (40cm in length) and living for up to 12 years. They can grow up to 100cm and 34kg in weight but are rarely found larger than 80cm and 10kg. They spawn all year round and have a medium to high resilience to fishing.

Stock information

Criterion score: 0.25 info

Skipjack tuna is a notoriously difficult species to assess. With some uncertainty, it is thought that the stock is not overfished and not subject to overfishing. Improved stock assessments are crucial for this stock. Skipjack has medium resilience to fishing pressure.

The skipjack stock in the Eastern Pacific Ocean (EPO) is assessed by the Inter-American Tropical Tuna Commission (IATTC). Due to its high and variable productivity, it is difficult to detect the effect of fishing on the population with standard methods. This is particularly true for the stock of the EPO, where there is a lack of data. There are a number of methods employed to assess skipjack.

The main method is to use the stock status of bigeye tuna. Skipjack and bigeye tuna have similar characteristics: skipjack is thought to have a similar level of susceptibility and a higher level of productivity. Therefore, skipjack stock status can be inferred from bigeye, and would be more optimistic and have a lower probability of exceeding reference points that bigeye. This only holds true as long as bigeye fishing mortality is below the MSY level. The 2018 assessment of bigeye indicated that the stock is subject to overfishing, but a new bigeye assessment was done in 2020. It was not conclusive, but it is clear the fishing pressure was increasing and stock biomass decreasing. IATTC have used the 2020 assessment to infer skipjack status. They have concluded that there is a less than 50% probability that the stock is subject to overfishing, and a less than 53% probability that it is in an overfished state. There is a less than 10% probability that limit reference points have been exceeded. These inferences about skipjack stock status from the PSA analysis are interim and direct advice from a skipjack assessment is still needed.

While this indicates that the stock is not subject to overfishing and not overfished, it is likely that fishing mortality on skipjack is increasing owing to the increase in the use of floating objects, or fish aggregating devices (FADs), which are responsible for about 70% of the total catch. Other indicators for skipjack have been developed, and all of them suggest that the stock status could be at risk of declining. These indicators use average values from 2000-2019 as a reference point:
Total catch: Catches of skipjack have steadily increased from around 60,000 tonnes in the 1980s to 350,000t in 2019 - the highest on record. They are above the average and increasing.
Catch per unit of effort (CPUE, based on catch per purse-seine-set): CPUE on FADs is below the average and declining. However, CPUE on free-schooling tuna (29% of total catches) is above the average and increasing.
Average length of skipjack caught: lengths are below the average and declining.

IATTC is currently conducting a multi-year tagging study of tropical tunas in the EPO aimed at obtaining data that will contribute to, and reduce uncertainty in, tuna stock assessments, particularly for skipjack. In addition, an MSE process for tropical tunas, which includes skipjack, is ongoing at IATTC.

Management

Criterion score: 0.75 info

East Pacific skipjack is not well understood, and management cannot be truly science-based until there are better stock assessments available. While the stock is not thought to be overfished or subject to overfishing, fishing mortality is increasing and there are no catch limits. The primary measure has been effort limits on the purse seine fishery (responsible for 99% of catches).

Most tuna stocks range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. To try and achieve this, Intergovernmental Regional Fisheries Management Organisations (RFMOs) have been established. There are five main tuna RFMOs worldwide and it is their responsibility to carry out data collection, scientific monitoring and management of these fisheries. This stock is managed and assessed by the Inter-American Tropical Tuna Commission (IATTC). Whilst the RFMOs are responsible for the development of management and conservation measures, the degree to which they are implemented, monitored and enforced still varies significantly between coastal states. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.

Management of tropical tunas (bigeye, yellowfin, and skipjack) in the Eastern Pacific is based on measures that last for three years. The current measures run from 2017-2020. At the 2020 IATTC commission meeting, the planned rollover of these measures to 2021 was blocked by one country, although a subsequent emergency meeting has resulted in them being extended until the end of 2021. Measures include:
A 30-day closure to large purse seiners of an area known as the “Corralito” (west of the Galapagos Islands, where catch rates of small bigeye are high) in October-November. Either before or after this, an additional 72-day closure in the whole IATTC area.
A limit on Fish Aggregating Devices, which catch high numbers of juvenile yellowfin and bigeye and are the main cause of increasing fishing pressure on all three tropical tunas. Limits per vessel range from 70 to 450, depending on vessel size. There were concerns about practicality of these limits, as accurate real-time monitoring of FAD versus non-FAD sets is challenging. It was recommended instead that the combined number of purse seine sets (FAD and non-FAD) should be limited to 2015-2017 average numbers (a 13% decrease on 2018 levels), with only dolphin-associated sets allowed once this limit is reached. In addition, the FAD limits were considered to be arbitrary and too high, and should be reduced by 30%.
Bigeye catch limits for longliners (varying by country). The scientific committee advises that if adequate management is in place for bigeye, this should also protect the skipjack stock.
A requirement to retain and land all bigeye, skipjack, and yellowfin tuna caught by purse seiners.
These measures represent the primary controls on catches and fishing effort for tropical tunas, and without them these fisheries will be effectively unregulated. Information on additional management measures is below.

In 2016, interim Harvest Control Rules were brought in for bigeye, skipjack and yellowfin purse seine fisheries, with the aim of preventing fishing effort from exceeding FMSY for the species that requires the strictest management. For other fisheries, management measures will be as consistent as possible with those for the purse seine fishery. Skipjack, yellowfin and bigeye stock assessments are too uncertain to produce values for fishing mortality, and stock status indicators are used instead. Indications are that fishing mortality is increasing on all three species owing to increases in purse seine fishing effort, specifically on floating objects. There are plans to evaluate this HCR and assess alternatives, so that a permanent HCR can be adopted.

The scientific committee considers it essential that fleet capacity does not increase beyond current levels. In 2002, regulations were implemented to freeze purse seine fleet capacity, but this has not been successful. Fleet capacity in 2017 was estimated to be about 6.7% greater than the previous three-year average. In 2017, it was acknowledged that the commission had failed since 2013 to reduce fishing mortality of yellowfin and bigeye (adjusted for capacity) to a level not exceeding MSY.

There is 100% observer coverage on large purse seiners. The scientific committee continues to recommend 20% observer coverage for small purse seiners, to obtain better data on discards and bycatch, as well as investigations into an electronic monitoring system on all purse seiners for better data on species, sizes, and quantities of target and bycatch species. Since 2011 only 5% observer coverage has been required on large longliners, considered by the scientific committee to be too low for accurate data: a minimum of 20% coverage is recommended. In addition, data recorded by longliners is considered inadequate for scientific purposes and minimum data standards must be identified and introduced.

To help address IUU, the IATTC maintains an IUU Vessel List; maintains a register of authorised fishing vessels; and prohibits transhipments at sea for most vessels (some exemptions apply) and requires most other transhipments to 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. However, IATTC is the only tuna RFMO not to have adopted Port State measures to strengthen work to tackle IUU. IATTC does not report on countries’ compliance with management measures and does not have a framework for addressing non-compliance.

The IATTC and WCPFC endeavour to work together to promote compatibility between their respective conservation and management measures across the Pacific.

Capture Information

Criterion score: 0.75 info

99% of the skipjack landings in the Eastern Pacific Ocean (EPO) are from purse seining: 70% on floating objects including Fish Aggregation Devices (FADs), and 29% on free schooling fish. Purse seining is associated with bycatch of species such as sharks, turtles and marine mammals, although less so than longlining. Whilst bycatch may comprise a small proportion of the total catch, the high volume of tuna that is caught means that it can still be significant for these vulnerable species. Bycatch is higher where Fish Aggregation Devices are being used. Poorly-designed FADs can entangle vulnerable species, and can also become lost at sea, continuing to ghost fish and be a source of marine debris. Some management is in place, but better data is needed to understand and control impacts.

The widespread use of FADs is also of concern due to the unknown impacts such gear might have on natural species composition of tuna schools, migratory patterns, growth rates and predation rates of affected pelagic species. Juvenile and bigeye tuna are caught by purse seining, and scientific recommendations are for these impacts to be reduced to protect the stocks. IATTC has limits on how many FADs a vessel can use for tropical tunas, although these limits are (at the time of writing) set to expire at the end of 2020. Scientific recommendations have been that the limits are too high and should be reduced (see Management tab). Bycatch mitigation measures such as sorting grids and non-entangling design are required to reduce mortality of turtles, sharks and non-target species in general. Countries must report details relating to FAD design, deployment, catch and bycatch. Biodegradable materials are encouraged, but not required. 100% observer coverage is required for large purse seine vessels, but there is no requirement for small purse seiners and scientists have repeatedly recommended a requirement for 20% coverage. This would improve reporting on bycatch.

Marine mammals: In the EPO, there is an active dolphin-associated purse seine fishery for yellowfin. There is a separate rating for this fishery. There are no other measures specifically to protect cetaceans. 778 dolphins and other mammals were killed by the fishery in 2019.

Turtles: IATTC note that tuna fisheries in the Eastern Pacific are having an adverse effect on sea turtle populations. If a turtle is caught, or encircled by a net, it must be safely released. All interactions should be recorded. There is some work underway to improve observer coverage, reduce turtle bycatch and investigate fishery closures near nesting beaches. The purse seine fishery is not a significant threat to turtle populations: out of 989 recorded interactions on large purse seiners in 2019, there were just 2 recorded mortalities.

Sharks: In 2018, all forms of purse seining combined caught 505 tonnes of sharks. Longlining caught 13,680t. Catches, mainly of silky, oceanic whitetip, hammerhead, and mako, are generally greatest in FAD fisheries, followed by free-school sets and, at a much lower level, dolphin sets. Many sharks are deliberately targeted, and so RFMO management must cover active shark fisheries as well as bycatch in tuna fisheries. However, sharks are vulnerable to fishing pressure, being slow-growing and late to mature. Some are listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). For fisheries specifically targeting sharks, countries are required to develop management plans, demonstrating how they intend to avoid or reduce catches of highly depleted shark species. There is a ban on shark finning, and a prohibition to land silky and oceanic whitetip sharks and mobula rays. Purse seining in the eastern Pacific Ocean caught 69 tonnes of mobula rays, below the long term average of 115t. Mobulid rays are of special concern because of their low reproductive rates. Any shark (whether alive or dead) caught that is not retained must be safely released. Tunas tend to aggregate around whale sharks, so vessels are prohibited from knowingly setting a purse seine a live whale shark and must release it if caught. Whale shark interactions are not common in this fishery. Fishing in silky shark pupping areas is prohibited, although these areas do not appear to have been clearly defined. In 2016 IATTC introduced stricter monitoring and reporting of catches of shark species, but the scientific committee continues to advise that shark data collection is inadequate and must be improved - it is currently not possible to assess the state of most sharks and mobulid ray species. The scientific committee also recommends that experiments be conducted on mitigating bycatches of sharks, especially in longline fisheries, and on the survival of sharks and mobulid rays captured by all gear types, with priority given to those gears with significant catches.

References

ACAP, 2019. ACAP Review and Best Practice Advice for Reducing the Impact of Pelagic Longline Fisheries on Seabirds, Reviewed at the Eleventh Meeting of the Advisory Committee of the Agreement on the Conservation of Albatrosses and Petrels, 13 - 17 May 2019, Florianopolis, Brazil. Available at https://www.acap.aq/en/bycatch-mitigation/mitigation-advice/3498-acap-2019-review-and-best-practice-advice-for-reducing-the-impact-of-pelagic-longline-fisheries-on-seabirds/file [Accessed on 29.11.2019].

Dias, M. P., Martin. R., Pearmain, E., J., Burfield, I. J., Small, C., Phillips, R. A., Yates, O., Lascelles, B., Garcia Borboroglu, P. and Croxall, J. P., 2019. Threats to seabirds: A global assessment. Biol. Cons. 237, pp 525-537. https://doi.org/10.1016/j.biocon.2019.06.033 [Accessed on 29.11.2019].

Froese R. and Pauly D. (Editors), 2019. Katsuwonus pelamis, Skipjack tuna. Available at: https://www.fishbase.de/summary/Katsuwonus-pelamis.html [Accessed on 15.12.2020].

Griffiths, S. and Fuller, L., 2019. Ecosystem considerations. Document SAC-10-14 presented to the Inter-American Tropical Tuna Commission Scientific Advisory Committee Tenth Meeting, 13-17 May 2019, San Diego, California, USA. Available at https://www.iattc.org/Meetings/Meetings2019/SAC-10/Docs/_English/SAC-10-14_Ecosystem%20considerations.pdf [Accessed on 03.12.2019].

IATTC, 2020. Inter-American Tropical Tuna Commission: Active IATTC and AIDCP Resolutions and Recommendations. Available at https://www.iattc.org/ResolutionsActiveENG.htm [Accessed on 14.12.2020].

IATTC, 2020. Report On The Tuna Fishery, Stocks, And Ecosystem In The Eastern Pacific Ocean In 2019. IATTC-95-05 presented to the Inter-American Tropical Tuna Commission 95th Meeting, 30 November - 4 December 2020, Online. Available at https://www.iattc.org/Meetings/Meetings2020/IATTC-95/Docs/_English/IATTC-95-05_The%20fishery%20and%20status%20of%20the%20stocks%202019.pdf [Accessed on 14.12.2020].

IATTC, 2020. Staff Recommendations for Management and Data Collection, 2020. IATTC-95-01 presented to the Inter-American Tropical Tuna Commission 95th Meeting, 30 November - 4 December 2020, Online. Available at https://www.iattc.org/Meetings/Meetings2020/IATTC-95/Docs/_English/IATTC-95-01-MTG_Conservation%20recommendations%20by%20the%20Commission%20staff.pdf [Accessed on 14.12.2020].

ISSF, 2020. Position Statement 2020-02: IATTC. presented to the Inter-American Tropical Tuna Commission 95th Meeting, 30 November - 4 December 2020, Online. Available at https://iss-foundation.org/downloads/21177/ [Accessed on 15.12.2020].

ISSF, 2020. Status of the world fisheries for tuna. Nov. 2020. ISSF Technical Report 2020-16. International Seafood Sustainability Foundation, Washington, D.C., USA. Available at https://iss-foundation.org/knowledge-tools/technical-and-meeting-reports/download-info/issf-2020-16-status-of-the-world-fisheries-for-tuna-november-2020/ [Accessed on 10.12.2020].

Lopez, J., Lennert-Cody, C., Maunder, M., and Aires-da-Silva, A., 2019. Adjusting current fad limits to meet 2019 staff recommendations for tropical tuna management in the Eastern Pacific Ocean. Document FAD-04-01 presented to the Inter-American Tropical Tuna Commission Ad-Hoc Permanent Working Group on Fads Fourth Meeting, 19 July 2019, Bilbao, Spain. Available at https://www.iattc.org/Meetings/Meetings2019/IATTC-94/Docs/_English/FAD-04-01_Active%20FAD%20limits.pdf [Accessed on 03.12.2019].

Wallace, B., 2019. A call for collaboration between IAC and IATTC to save Eastern Pacific leatherbacks. Presented to the Inter-American Tropical Tuna Commission Scientific Advisory Committee Tenth Meeting, 13-17 May 2019, San Diego, California, USA. Available at https://www.iattc.org/Meetings/Meetings2019/SAC-10/BYC-09/Presentations/BYC-09-PRES_A%20call%20for%20collaboration%20between%20IAC%20and%20IATTC%20to%20save%20Eastern%20Pacific%20leatherbacks.pdf [Accessed on 02.12.2019].