Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Purse seine (FAD & Free School)
Capture area — Pacific, North West (FAO 61) and Central (FAO 71,77)
Stock area — Western and Central Pacific
Stock detail — All Areas
Picture of Tuna, skipjack

Sustainability rating three info

Sustainability overview

Updated: November 2020

The Western and Central Pacific Ocean (WCPO) skipjack stock supports the largest tuna fishery in the world, accounting for approximately 37% of worldwide tuna landings. It is not subject to overfishing, but the stock size is slightly below target levels and is projected to decline under current catch levels. A Harvest Control Rule is to be developed for skipjack. Until then, management measures are mainly aimed at limiting fishing effort by purse seiners, which is responsible for around 80% of the skipjack catch. There are also limits on the number of large longliners allowed to fish for skipjack. Observers, to verify catch and bycatch, are on 100% of purse seiners within the main fishing grounds, but coverage is low for other areas and gear types at just 5%. There is not enough data to be sure that countries are complying with the management measures. Purse seine fishing accounts for 80% of skipjack tuna catches in the Western and Central Pacific Ocean (WCPO). Around 37% uses Fish Aggregating Devices (FADs) and 43% is on free schools. 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 reduce impacts to vulnerable species and encourage development of a harvest strategy for skipjack. Large buyers should consider supporting such improvements. There are MSC certified fleets within the scope of this rating which represent the best choice and there is also is a Fishery Improvement Project (FIP) in place for some fleets. More info is available from fisheryprogress.org.

MCS advocates specifying the need for supplying vessels to register on the ISSF Proactive Vessel Register.

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 info

The Western and Central Pacific Ocean (WCPO) skipjack stock supports the largest tuna fishery in the world, accounting for approximately 37% of worldwide tuna landings. It is not subject to overfishing, but the stock size is slightly below target levels and is projected to decline under current catch levels.

This stock is managed and assessed by the Western and Central Pacific Fisheries Commission (WCPFC). The latest stock assessment was carried out in 2019 using data up to 2018. Skipjack tuna catches in the WCPO increased steadily from 1970 onwards, roughly doubling during the 1980s. After stabilising at around 1 million tonnes during the early 1990s, they increased to a record catch of around 2 million tonnes in 2014. Catches have since levelled off at around 1.75 million tonnes. Fishing mortality (F) has correspondingly increased, peaking in 2018 at 45% of levels associated with Maximum Sustainable Yield (MSY). There is zero probability that F exceeds FMSY, meaning that the stock is not subject to overfishing. Biomass has declined from about 90% of unfished levels in 1970 to 44% in 2018. There is a Target Reference Point of 50% of unfished levels. While this puts the stock below the target level, the stock assessment concludes that the stock is not overfished because it is above the Limit Reference Point of 20%. Spawning biomass is around 2.5 times the level associated with MSY (SBMSY), but fishing mortality is continuously increasing and SB has reached its lowest level on record. The scientific committee therefore recommends that management is implemented to keep the biomass fluctuating around the TRP, e.g. through a Harvest Control Rule.

The skipjack catch in 2018 (1,795,048t) was a 10% increase from 2017 and a 1% decrease from the 2013-2017 average. If 2012 purse seine effort levels (and 2012 catches for other gear types) are maintained, SB is projected to decrease to 42% of unfished levels. To keep the stock at between 44% and 50% of unfished levels, effort must be reduced from 2012 levels by 7-25%. This would lead to increases in spawning biomass of between 3% and 18%.

The scientific committee advises that tagging data is a critical component of the skipjack stock assessment and recommend regular large-scale tagging cruises and complementary tag recovery work continue to be undertaken in a way that provides the best possible data for stock assessment purposes.

Management

Criterion score: 0.5 info

The Western and Central Pacific Ocean (WCPO) skipjack stock supports the largest tuna fishery in the world, accounting for approximately 37% of worldwide tuna landings. It is not subject to overfishing, but the stock size is slightly below target levels and is projected to decline under current catch levels. A Harvest Control Rule is to be developed for skipjack. Until then, management measures are mainly aimed at limiting fishing effort by purse seiners, which is responsible for around 80% of the skipjack catch. Observers, to verify catch and bycatch, are on 100% of purse seiners within the main fishing grounds, but are low for other areas and gear types at just 5%. There is not enough data to be sure that countries are complying with the management measures.

Most tuna stocks range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. As a result, 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. The tuna fisheries in the Western and Central Pacific Ocean (WCPO) are managed by the Western and Central Pacific Fisheries Commission (WCPFC). 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. 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. In addition, around 50% of West Pacific purse-seine-caught skipjack and 70% of yellowfin is certified by the Marine Stewardship Council.

WCPFC is looking to establish harvest strategies for key fisheries and stocks but has not yet completed this work and so a bridging measure is in force to manage bigeye, yellowfin and skipjack. It lasts from 2018 until harvest strategies are in place, or February 2021. There is a limit reference point for the spawning biomass of bigeye, skipjack, and yellowfin tuna of 20% of unfished levels (SB/SBF0 = 0.2), below which the stock should not fall. Skipjack also has an interim target reference point of 50% of unfished levels, while bigeye and yellowfin are to be maintained at recent levels (the average from 2012-2015). Skipjack is slightly below the target, at 44%, and is projected to decline under current catch levels. Recent effort levels in terms of numbers of sets in the tropical purse seine fishery have been 87% (2015-2018 average) and 98% (2019 levels) of those in 2012.

An evaluation of the bridging measure in 2019 found that it would achieve its targets if bigeye recruitment remains high, but if that declines, fishing mortality will double to above FMSY and biomass has a 20% chance of dropping below the limit reference point. For yellowfin, the measure will marginally fail its aims as SB will experience a small decrease. The bridging measure includes a number of new measures and consolidates some pre-existing ones. It isn’t clear how well they have been implemented, especially given the ongoing increases in total catch of skipjack. The scientific committee recommends more comprehensive data collection relating to FADs. It also recommends reducing fishing mortality on juveniles by preventing increases in overall fishing mortality. In the tropical region, between 20 degrees North and 20 degrees South, the following applies:
FADs are banned for 5 months of the year (3 months for Kiribati and the Philippines). VMS polling frequency increases to every 30 minutes during the FAD closure.
Effort limits (in vessel days) apply to purse seining on the high seas (excluding Small Island Developing States, SIDS). Limits vary by country. Effort shouldn’t be transferred into areas outside of the bridging measure. Large purse seine and longline vessel numbers and capacity are frozen to 2016 levels (excluding SIDs and Indonesia).
Purse seiners must retain and land all bigeye, skipjack, and yellowfin tuna. This is intended to incentivise reductions in bycatch of juvenile fish.
100% observer coverage is required for purse seine vessels. Outside of the areas covered by the bridging measure, observer coverage on purse seiners is poor. Only 5% coverage is required on longliners greater than 20m in length. 20% is considered to be the minimum to be effective.

Other measures that apply to tuna in the wider convention area:
Each purse seine vessel is limited to 350 drifting FADs at a time. Countries should have FAD management plans, with strategies to implement closures and other measures for reducing mortality of juvenile bigeye.
Catch and/or effort limits apply to purse seining within national waters (it varies by country). For bigeye, there are country-specific limits on longline catch. By 2020, limits for bigeye and a framework to allocate them amongst countries should be developed. Catches by other fisheries for bigeye, yellowfin or skipjack tuna (except those taking less than 2,000 tonnes) are frozen to either the average level for 2001-2004 or the level of 2004.

More generally:
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.

Capture Information

Criterion score: 0.75 info

Purse seine fishing accounts for 80% of skipjack tuna catches in the Western and Central Pacific Ocean (WCPO). Around 37% uses Fish Aggregating Devices (FADs) and 43% is on free schools. 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. WCPFC limits how many FADs a country can use, and bans them for part of the year. To reduce the entanglement of sharks, marine turtles or any other species, and reduce the amount of synthetic marine debris, WCPFC requires the use of low-entanglement-risk FADs as of January 2020. It also encourages the use of biodegradable materials in the construction of FADs. Implementation of this is slow: a 2020 assessment indicated that 65–90% of FADs have nets attached, which are the main cause of entanglement. Natural and low or non-entangling dFAD materials are rarely used in the WCPO. FADs lost at sea can cause ghost fishing and wash up on reefs or beaches, adding to marine pollution. 100% observer coverage is required for purse seine vessels fishing for tropical tunas in the tropical region, between 20 degrees North and 20 degrees South. Outside of this and for other gears, observer coverage is poor. Only 5% coverage is required on longliners greater than 20m in length. 20% is considered to be the minimum to be effective.

Marine mammals: Cetaceans are particularly 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. 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.

Turtles: The five marine turtle species in the WCPFC Convention Area are threatened or critically endangered, and WCPFC does not hold sufficient information to quantify the severity of the threat posed by its fisheries to sea turtle populations. Countries should try not to encircle turtles with nets, and release them safely if they have. Comatose or inactive turtles should be recovered or resuscitated before release. Interactions must be recorded.

Sharks: 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). Redistribution of 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%). Shark measures include: no shark finning; a prohibition to land silky and oceanic whitetip sharks; and a prohibition on the use of shark lines. Tuna often swim with whale sharks; deliberately setting a net on a whale shark is prohibited. 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. There are measures to improve recording of manta and mobula rays discarded and released, and to treat these species as key shark species for assessment and research. Guidelines for safe release of manta and mobulid rays were adopted in 2017. The commission is also looking to develop guidelines for other rays and sharks, and develop stronger and more comprehensive management measures for sharks, but there is no stated deadline for this. No limit reference points are in place for any Pacific sharks, and it is recommended that these be implemented.

Shark species of concern are:
Silky sharks, which are subject to overfishing. In 2016, catches of silky sharks in the longline fishery were around three times higher than in the purse seine fishery.
Pacific bigeye thresher, which seems likely to be experiencing overfishing, primarily from the bigeye tuna fleet.
Oceanic whitetip, which is heavily overfished, at just 4% of unfished levels. This is a very slight recovery from previous years, but it’s unclear if recovery will continue. Fishing pressure is high but has declined. 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. Reduced catch and retention has occurred as a result of the existing management measures, but this has reduced the amount of data coming in about the species.

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].

Brouwer, S., Pilling, G., Williams, P., WCPFC Secretariat , 2017. Trends in the South Pacific albacore longline and troll fisheries, Document WCPFC-SC13-2017/SA-WP-08 for the Thirteenth Regular Session of the Scientific Committee of the Commission for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean, 9 - 17 August 2017, Rarotonga, Cook Islands. 70 pp. Available at https://www.wcpfc.int/meetings/sc13 [Accessed on 27.11.2017].

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].

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].

ISC, 2020. Report of the 20th Meeting of the International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean, 15-20 July 2020, online. 74pp. Available at http://isc.fra.go.jp/pdf/ISC20/ISC20_PLENARY_Report_FINAL.pdf [Accessed on 10.12.2020].

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].

Phillip, N.B. and Escalle, L., 2020. Updated evaluation of drifting FAD construction materials in the WCPO. WCPFC-SC16-2020/EB-IP-03 presented to the Western and Central Pacific Fisheries Commission Scientific Committee 16th Regular Session, 11-20 August 2020, Online. Available at https://www.wcpfc.int/node/46724 [Accessed on 11.12.2020].

SPC-OFP, 2020. Updates to WCPO Skipjack Tuna Projected Stock Status to Inform Consideration of an Updated Target Reference Point. WCPFC17-2020-11 presented to the Western and Central Pacific Fisheries Commission 17th Regular Session, 7 - 15 December 2020, Online. Available at https://www.wcpfc.int/node/48919 [Accessed on 11.12.2020].

WCPFC, 2020. Stock Status and Management Advice: Skipjack Tuna (Katsuwonus pelamis). Available at https://www.wcpfc.int/doc/03/skipjack-tuna [Accessed on 10.12.2020].

WCPFC, 2020. Summary Report of the Sixteenth Regular Session of the Scientific Committee of the WCPFC, 12-19 August 2020 (Reconvened on 10 September 2020), Online. Available at https://www.wcpfc.int/file/568072/download?token=hcPeql6u [Accessed on 10.12.2020].

WCPFC, 2020. Conservation and Management Measures of the Western and Central Pacific Fisheries Commission. Compiled 2 Nov 2020 - 09:46. Available at https://www.wcpfc.int/system/files/booklets/31/CMM%20and%20Resolutions.pdf [Accessed on 10.12.2020].