Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Purse seine (FAD & Free School)
Capture area — Atlantic, North (FAO 27), Central (FAO 34) and South (FAO 47) Eastern
Stock area — East Atlantic
Stock detail — All Areas
Picture of Tuna, skipjack

Sustainability rating four info

Sustainability overview

Updated: November 2020

Skipjack tuna are notoriously difficult to assess, and often there are high levels of uncertainty. There are two stocks of Atlantic skipjack: east and west. This rating is for the eastern stock, which hasn’t had a stock assessment since 2014 and owing to Covid disruption isn’t now due to receive the next one until 2022. In 2014, it was thought that the stock was unlikely to be in an overfished state, and unlikely to be subject to overfishing. However, concerns were raised at the time that catches could be above sustainable levels, and they have been consistently above recommended limits since then. As the 2014 stock assessment continues to be used for management advice, MCS has not changed stock scores, but remains concerned that overfishing could be taking place. There are no specific management measures for skipjack, and no catch limits. The main management measure of relevance is therefore controls on the use of certain gear (Fish Aggregating Devices) in the purse seine fishery. Catches are higher than recommended limits, and it is possible that they have been under reported. Existing management is not effective at controlling this fishery. Roughly 83% of eastern skipjack catch is by purse seine fishing. 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, which is around 90% of the purse seine catch in this fishery. FAD use is increasing. 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. There are measures in place requiring countries to improvement FAD management and reduce these impacts. All large purse seine vessels fishing for tropical tunas must have an observer, which improve understanding of bycatch and help to improve compliance with management measures.

Commercial buyers should establish what measures the flag state relating to their source is taking to improve data collection, research, monitoring and management of their fisheries and specify the need to see ongoing, demonstrable improvements. 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 four active Fishery Improvement Projects (FIP) in place which cover East Atlantic skipjack as well as bigeye and yellowfin tuna. There is also a completed purse seine FIP which is currently in Marine Stewardship Council assessment. In terms of the active FIPs, two are for pole and line and two for purse seine. The main purse seine FIP is the Eastern Atlantic Sustainable Tuna Initiative (EASTI). It runs from 2018-2023, and is behind schedule on several actions including ecosystem impacts. While progress has been made in some areas, the FIP has not taken direct action to limit the catches of its own fleets.

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 are notoriously difficult to assess, and often there are high levels of uncertainty. There are two stocks of Atlantic skipjack: east and west. This rating is for the eastern stock, which hasn’t had a stock assessment since 2014 and owing to Covid disruption isn’t now due to receive the next one until 2022. In 2014, it was thought that the stock was unlikely to be in an overfished state, and unlikely to be subject to overfishing. However, concerns were raised at the time that catches could be above sustainable levels, and they have been consistently above recommended limits since then. As the 2014 stock assessment continues to be used for management advice, MCS has not changed stock scores, but remains concerned that overfishing could be taking place. Skipjack has a medium resilience to fishing pressure.

Skipjack stocks in the Atlantic are assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The last stock assessment was carried out in 2014 using data up to 2013. It could not provide reliable estimate of a sustainable level of fishing (i.e. Maximum Sustainable Yield, MSY). It was considered unlikely that the eastern skipjack stock is overexploited, as there was no evidence of a fall in yield, or in the average weight of individuals captured. There was a steady decrease in average weight up to 2011, as most catches were by purse seiners, which were taking high numbers of juveniles. This trend has reversed since 2012, but average skipjack weight in the East Atlantic (2kg) is generally much lower than the estimates for other oceans (3kg), except in the East Pacific. The stock size and therefore MSY may have been increasing, but not as quickly as the increases in catches. East Atlantic catches have steadily increased since 1960, reaching a record 284,000t in 2018 and falling slightly to 245,124t (preliminary) in 2019. The 2015-2019 average catch is 246,000t, whereas scientific recommendations are for no more than 218,000 tonnes. In the 2014 assessment it was thought that catches could be at or above MSY, but the scientific committee concluded that fishing mortality (F) was unlikely to be above FMSY. No projections were available to indicate the effect of catches on the stock. At that point, the five-year average catch was 200,000t.

In order to overcome the challenges in carrying out stock assessments, several methods have been applied to the two stocks of Atlantic skipjack. Smaller sub-units of stocks are being considered and it is expected that the five year Atlantic Tropical Tuna Tagging Programme (AOTTP) may improve understanding of skipjack stock structures and movement patterns.

Underreporting has been a problem in the fishery, and corrections have been applied to try to account for this. There has been a sharp increase in purse seine catch, particularly on FADs, in part due to piracy in the Indian Ocean displacing fleets into the Atlantic. Estimates of the unreported catches of these purse seiners have increased since 2006 and may have exceeded 20,000 t for the three main species of tropical tunas. The scientific committee has expressed the need for the countries and the industry in the region to cooperate to estimate and report these catches accurately to ICCAT.

Management

Criterion score: 0.75 info

There are no specific management measures for skipjack, and no catch limits. The main management measure of relevance is therefore controls on the use of certain gear (Fish Aggregating Devices) in the purse seine fishery. Catches are higher than recommended limits, and it is possible that they have been under reported, leading to potential overfishing of this stock. Existing management is not effective at controlling this fishery.

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 address 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 International Commission for the Conservation of Atlantic Tunas (ICCAT). 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. There remain large data deficiencies in most tuna and billfish fisheries, particularly with regards to fine scale spatial and temporal data for both target and especially for vulnerable bycatch species. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.

In spite of scientific recommendations and attempts to develop a Harvest Control Rule (HCR) for eastern skipjack, there is no TAC (Total Allowable Catch) or HCR in place for this stock. The last stock assessment for eastern skipjack was in 2014, when no reliable estimate of the maximum sustainable yield (MSY) could be provided. It was considered unlikely that the stock was overfished or subject to overfishing. However, the committee stated that it was possible that current catches at the time were at or even above MSY. No projections were available to indicate the effect of those catches on this stock, but the committee recommended that the catch and effort levels should not exceed the levels in 2012-2013 (218,000 tonnes). At the time of the assessment, the five-year (2010-2014) average catch was 200,000t. East Atlantic catches have substantially increased since, reaching a record 284,000t in 2018 and falling slightly to 245,124t (preliminary) in 2019. The 2015-2019 average catch is 246,000t. The majority of this increase has been driven by increases in catches by the purse seine fishery. There may be under-reporting of skipjack catches, possibly exceeding 20,000 t for the three main species of tropical tunas. Management is therefore not appropriately monitoring or controlling this fishery. Scientists have advised that increasing catch and effort for skipjack could also lead to consequences for other species that are caught alongside them, e.g. juvenile yellowfin and bigeye.

There is concern about the impact of catching tuna using purse seine nets around fish aggregation devices (FADs). The increasing use of FADs in skipjack fisheries since the early 1990s has changed the species composition of free schools. It is noted that, in fact, free schools of mixed species were considerably more common prior to the introduction of FADs. It may also have negative consequences for adult yellowfin and bigeye tuna, as well as other by-catch species. Association with FADs may also have an impact on the biology (growth rate, plumpness of the fish) and on the ecology (distances, movement orientation) of skipjack and yellowfin (the “ecological trap” concept). Many juvenile fish are often caught in purse seine fisheries, mainly skipjack, yellowfin and bigeye. When a high proportion of young fish are removed from a population, the potential maximum catch from a fishery is reduced. The recent average weight in European purse seine catches, which represent the majority of the landings, has declined to about half of the average weight of 1990, at least in part due to the use of FADs and the increased catches of small yellowfin. A decline in average weight and size is also evident in eastern tropical bait boat catches, although longline catches have not seen the same trend. In 2015 a working group was formed to look at ways to reduce juvenile catches of bigeye and yellowfin tuna caught in FAD fishing, and countries must have FAD Management Plans that improve understanding of FADs and limit their impacts on the ecosystem. However, the scientific committee continues to recommend that more work needs to be done on this.

A multi-annual management programme has been in place for bigeye and yellowfin since 2012, and eastern skipjack since 2015, mostly focussed on FAD management. Fishing for these species using aggregation devices, including FADs, was prohibited from 1st January to 28th February in an area off the west African coast to reduce catches of juvenile bigeye and yellowfin, for the rest of the year vessels were limited to 500 FADs. This failed to reduce the mortality of juvenile bigeye and yellowfin tuna so in 2019, to address this, the number of FADs was reduced from 500 to 350 in 2020 and 300 in 2021. The FAD closure was extended to the full convention area, lasting 2 months in 2020 and 3 months in 2021. In 2020 the scientific committee advised that it was too soon to evaluate the impact of these changes.

The main other management measures for bigeye, skipjack and yellowfin, which are usually caught together, include:

There is a tagging programme to improve stock assessments for tropical tunas and gauge effectiveness of management measures for these species. This helped to improve the quality of the 2019 yellowfin assessment. In 2017 ICCAT banned the discarding of skipjack, yellowfin and bigeye, so that all fish caught must now be landed.

Other management by ICCAT includes:
ICCAT maintains a list of vessels over 20m authorised to fish for this species, although other vessels may retain them as bycatch as long as the country sets limits on this and doesn’t exceed its quota.
In 2019 ICCAT increased observer coverage: large purse seiners targeting tropical tunas must have 100% coverage year round rather than just during the FAD closures, and longline coverage will increase from 5% to 10% in 2022. However, the 5% coverage was not well complied with or enforced by some fleets (although others exceeded it), and even this increase falls short of recommendations for a minimum of 20% for accurate reporting of bycatch. However, standards for electronic monitoring are to be developed by 2021. Purse seine and longline vessels over 20m long are encouraged to increase their observer coverage from the required minimum, and some have. Vessel Monitoring Systems are required for all vessels over 24m.
Drift nets were banned by the EU in 2002 and by ICCAT in the Mediterranean in 2003.
In terms of enforcement and compliance with management measures: in 2016 ICCAT passed measures to strengthen and streamline its compliance assessment process and to develop a scheme of responses to non-compliance. There is also a list of vessels authorised to fish for tuna and tuna-like species in the ICCAT area, and a list of vessels caught carrying out Illegal, Unreported or Unregulated activities. At-sea transhipment is prohibited unless pre-authorised and the vessel has an observer on board.

There are four active Fishery Improvement Projects (FIP) in place which cover East Atlantic skipjack as well as bigeye and yellowfin tuna. There is also a completed purse seine FIP which is currently in Marine Stewardship Council assessment. In terms of the active FIPs, two are for pole and line and two for purse seine. The main purse seine FIP is the Eastern Atlantic Sustainable Tuna Initiative (EASTI). It runs from 2018-2023, and is behind schedule on several actions including ecosystem impacts. Some collaborative work has been done to build consensus and advocate for robust harvest strategies these to ICCAT. The FIP has also reviewed its fleets’ compliance with ICCAT regulations, in order to develop additional actions where compliance is poor. However, the FIP has not taken direct action by implementing its own harvest strategy or catch limits, and this is of particular concern to MCS. Some progress has been made on recording and mitigating impacts on vulnerable species. Some codes of practice and voluntary agreements are in place to minimise ecosystem impacts. The Ghanaian pole and line and purse seine fleets are carrying out a trial to develop biodegradable FADs. The Ghanaian pole and line FIP runs from 2018-2023. MCS has concerns about the rate of progress of this FIP and its ability to address the key issues, including harvest strategies for the stock and mitigating impacts of the baitfishery. It has made some attempt to work with other FIPs relating to harvest control rules, but in September 2020 reported that “A conducive conclusion could not be reached in conjunction with the EASTI purse seine FIP participants and talks were therefore halted.” It has made no progress on improving understanding and management of baitfish. The fleet has 100% observer coverage but hadn’t been recording the use of baitfish. The Senegalese pole and line FIP runs from 2019-2024. It faces similar challenges to the Ghanaian FIP, but seems to have made better progress. It intends to install an electronic monitoring system for better monitoring of the fishery and is working with the EASTI FIP to influence stock assessment and harvest strategies. This includes a joint position paper for ICCAT strongly supporting the development of harvest strategies and formal management procedures. There is an intention to develop a national management plan for baitfish.

Capture Information

Criterion score: 0.75 info

Roughly 83% of eastern skipjack catch is by purse seine fishing. 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, which is around 90% of the purse seine catch in this fishery. FAD use is increasing. 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. There are measures in place requiring countries to improvement FAD management and reduce these impacts. All large purse seine vessels fishing for tropical tunas must have an observer, which improve understanding of bycatch and help to improve compliance with management measures.

Purse seining is commonly an industrial scale fishery used to catch tuna destined for canneries. Skipjack are captured in association with bigeye and yellowfin tuna. It is difficult to discriminate fishing effort between free schools (composed of large yellowfin tunas) and for FAD fishing (targeting skipjack) in the East Atlantic because fishing strategies can change from one year to the next. In addition, the sea time devoted to activities on FADs and the assistance provided by supply vessels are difficult to quantify. Purse seining tends to catch smaller (and therefore younger) tuna than longlining. The proportion of small fish in the catches of East Atlantic skipjack since the onset of FADs has significantly increased, and average retained skipjack weight observed here is approximately 2kg whereas estimates in other oceans are closer to 3kg. Scientists have advised that increasing catch and effort for skipjack could also lead to consequences for other species that are caught alongside them, e.g. juvenile yellowfin and bigeye tunas. Scientists have repeatedly advised that effective measures are needed to reduce fishing mortality on small yellowfin, and bigeye is overfished and subject to overfishing. Therefore, FAD management is an important tool to manage the impacts of this fishery.

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. In order to minimize the ecological impact of FADs, in particular the entanglement of sharks, turtles and other non-targeted species, and reduce marine pollution from lost gear, countries must use non-entangling FADs and phase out non-biodegradable FADs. Countries must also have FAD Management Plans that improve understanding of FADs and limit their impacts on the ecosystem.

Other management in place to protect vulnerable species include:

For sharks: Countries are required to develop and submit National Plans of Action for the conservation and management of sharks. Sharks must be fully utilised (e.g. no removal of fins); must be released wherever possible (if not being directly targeted); and countries must try to minimise bycatch of sharks (although no gear-specific measures are identified). Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako, which is heavily overfished, can be caught and retained if over 180cm for males and 210cm for females, otherwise, they must be released unharmed. An updated assessment in 2019 indicated that shortfin mako is unlikely to recover to healthy levels until 2070, unless size restrictions combined with a fixed Total Allowable Catch were introduced. The maximum catch that would allow recovery by 2070 with a reasonable probability (60%) was 300 tonnes. Regardless of management measures, the stock will continue to decline until 2035. However, in 2019 ICCAT failed to reach agreement on measures to protect this species. For blue shark, catch limits are now in place for both northern (39,102t as of 2016) and southern (28,923t as of 2016) stocks, with the northern TAC being allocated to countries - a first for ICCAT shark stocks. If exceeded, the commission has committed to reviewing the effectiveness of its blue shark management measures, although preliminary catch of northern blue shark in 2016 was 42,117 t. Porbeagle is significantly so in the northwest Atlantic and stock status in the northeast and south Atlantic is unknown. In the northwest, the stock could recover by 2035 under recent catches, but these are likely to be underestimated because dead discards are rarely reported. The main porbeagle-directed fisheries (EU, Uruguay and Canada) have closed, and ICCAT have a recommendation to release live porbeagle unharmed, but it is still caught incidentally and discarded, and also landed by other fleets. Currently there is not enough data to properly assess the status of many pelagic sharks (no assessments have been carried out for the Mediterranean) and more work is needed to understand the effects of entanglement in FADs.

For turtles: Purse seiners must avoid encircling turtles and release them when they do so. The scientific committee has noted that management or turtle bycatch is only in place for purse seine and longline. Measures for other gears are needed to both coordinate methods to avoid them, and to improve data on bycatch.

For marine mammals: there are no specific management measures to protect marine mammals, including cetaceans. ICCAT has not prioritised collecting data on mammal bycatch to date. More needs to be done to understand and reduce the impact of ICCAT fisheries on marine mammals.

In 2019 it was agreed to increase observer coverage for large purse seiners targeting tropical tunas to 100% coverage year-round rather than just during the FAD closures, which is a positive improvement.

References

EC, 2019. European Commission Press: Good news for tuna and blue sharks, 29.11.2019. Available at https://ec.europa.eu/fisheries/press/good-news-tuna-and-blue-sharks_en [Accessed on 09.12.2019].

ICCAT, 2020. Resolutions, Recommendations and other Decisions. Available at http://www.iccat.es/en/RecsRegs.asp [Accessed on 26.11.2020].

Froese R. and Pauly D. (Editors), 2019. Katsuwonus pelamis, Skipjack tuna. Available at: https://www.fishbase.de/summary/Katsuwonus-pelamis.html [Accessed on 02.12.2020].

ICCAT, 2020. 2020 SCRS Advice to the Commission, September 2020, Madrid, Spain. 362pp. Available at https://www.iccat.int/Documents/SCRS/SCRS_2020_Advice_ENG.pdf [Accessed on 26.11.2020].

ICCAT, 2020. Report of the 2020 ICCAT Intersessional Meeting of the Sub-Committee on Ecosystems, 4-6 May 2020, Online. 28pp. Available at https://iccat.int/Documents/Meetings/Docs/2020/REPORTS/2020_SC_ECO_ENG.pdf [Accessed on 26.11.2020].

ISSF, 2019. International Seafood Sustainability Foundation Blog: ICCAT Moves to Protect Atlantic Bigeye and Close Gaps in Monitoring and Data Collection, 4 December 2019. Available at https://iss-foundation.org/iccat-moves-to-protect-atlantic-bigeye-and-close-gaps-in-monitoring-and-data-collection/ [Accessed on 09.12.2019].

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].

IPNLF, 2012. Ensuring sustainability of live bait fish, International Pole and Line Foundation, London, 57 pp.

ISSF, IPNLF, 2019. Skippers’ Guidebook to Pole-and-Line Fishing Best Practices. Version 1.0 - April 2019. International Seafood Sustainability Foundation and International Pole & Line Foundation. Available at http://ipnlf.org/perch/resources/pl-guidebookipnlfissffinal.pdf [Accessed on 30.11.2020].

FIP DOCUMENTATION:
Defaux V., Gascoigne J. and Huntington T., 2018. MSC pre-assessment of a Ghana based pole and line tuna fishery. 72 pp. Available at https://fisheryprogress.org/system/files/documents_assessment/1435R01B%20TUE%20Poseidon%20GHA%20PL%20pre%20assess_v3_20180316.docx [Accessed on 02.12.2020].

Key Traceability Ltd., 2020. Fishery Progress Six Month Update for the Ghana Tuna Pole and Line Fishery Improvement Project. Project ref: 0080. Prepared by by Key Traceability Ltd. September 2020. Available at https://fisheryprogress.org/system/files/documents_additional/Six%20month%20action%20updates%20for%20Ghana%20P%26L%20FIP%20-%20September%202020.pdf [Accessed on 02.12.2020].

Fishery Progress, 2020. Eastern Atlantic Ocean tuna - pole & line: Actions Progress. Available at https://fisheryprogress.org/node/11420/actions-progress [Accessed on 02.12.2020].

Key Traceability Ltd., 2020. Fishery Progress Annual Update for the Eastern Atlantic Sustainable Tuna Initiative (EASTI) Fishery Improvement Project. Project ref: 0079. Prepared by by Key Traceability Ltd. June 2020. Available at https://fisheryprogress.org/system/files/documents_additional/Annual%20action%20updates%20for%20EASTI%20FIP%20-%20June%202020.pdf [Accessed on 02.12.2020].

Fishery Progress, 2020. Eastern Atlantic tuna - purse seine: Actions Progress. Available at https://fisheryprogress.org/node/7547/actions-progress [Accessed on 02.12.2020].