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 2019 

Skipjack tuna is a notoriously difficult species to assess, as its high and variable productivity makes it difficult to detect the effect of fishing on the population. This is compounded in the Eastern Pacific Ocean (EPO) by a lack of data, which is being addressed through a tagging study from 2019-2023. Data limited scoring has been applied for assessing stock status. The scientific committee advises that if a levelling off of catch or Cath Per Unit Effort (CPUE) occur, it may indicate that the exploitation rate is near or above the level associated with MSY. However, there is a significant amount of uncertainy surrounding all possible indicators relating to the level of fishing pressure. There is no concern for the biomass, as according to the scientific committee, the indicators have yet to detect any adverse impacts of the fishery. Therefore, MCS considers that there is curently no concern for fishing pressure or biomass.

Management measures include capacity limits for purse seiners, interim Harvest Control Rules, seasonal closures and restrictions on the number of floating objects the purse seine fishery can use. However, these have failed to limit fishing pressure on bigeye, skipjack and yellowfin tuna, and in 2019 indications are that fishing mortality is increasing on all three species. This is primarily owing to increases in purse seine fishing effort, specifically on floating objects.

Less than 1% of EPO skipjack catch is taken by troll, and pole and line boats. These fisheries are labour intensive yet very selective and low impact to the marine ecosystem. Pole and line fisheries depend on significant quantities of bait fish to attract the tuna. Whilst these bait fish are usually small, resilient species, some basic monitoring and management measures need to be developed.

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. FAD-associated purse seining generally encounters higher bycatch rates than sets on free-schools, and higher proportions of juvenile tuna. Most bigeye tuna purse-seine catch is from the FAD skipjack fishery: bigeye tuna is in an overfished state, with overfishing occurring, and fishing morality needs to be reduced on this species. The proportion of bycatch of vulnerable species is low in purse seine fisheries in the EPO (less than 0.5% for sharks), yet the overall catch of sharks is still significant and better monitoring and reporting is needed. FADs can also entangle sharks and turtles, but FAD construction and overall management is improving. There is 100% observer coverage on large purse seiners, but small purse seiners have no observer requirement and data from them is very poor.

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

Stock Area

Eastern Pacific

Stock information

The skipjack stock in the Eastern Pacific Ocean (EPO) is assessed by the Inter-American Tropical Tuna Commission (IATTC). Skipjack tuna is a notoriously difficult species to assess. 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. Therefore, data limited scoring has been applied to assess stock status. Skipjack has medium resilience to fishing pressure, and there appears to be no concern for fishing pressure or biomass.

According to the scientific committee, of primary concern for this stock is the constantly increasing exploitation rate, but this appears to have levelled off in recent years and consequences have not emerged. While biomass and recruitment appear to have been increasing over the past 20 years, this is based on unreliable and probably optimistic Catch per Unit Effort (CPUE) data, and therefore is probably an inflated estimate. However, there is no concern for the biomass, as according to the scientific committee, the stock indicators have yet to detect any adverse impacts of the fishery.

The scientific committee state that it is unknown if the current fishing mortality levels are appropriate because there is no reference point, but that a levelling off of catch or Catch per Unit of Effort (CPUE) may indicate that the exploitation rate is near or above the level associated with MSY. With regard to catches: following record high levels (342,500t in 2016), catches have declined to around 288,000t in 2018, below the 5 year average (311,000t) and close to the recent 10-year average (279,000t). With regard to CPUE: this is measured as Catch per Days Fished, which has generally increased but declined in the last 2-3 years. However, Catch per Days Fished is probably overestimated, because there has been an increase in the number of floating-object purse seine sets that have been put out per day. Catch per set (which would be another way to measure CPUE) has fallen.

The average weight of skipjack has been declining since 2000, reaching levels last seen in the early 1980s. In 2015 and 2016 it was below the lower reference level (although this is likely due to large recruitments in 2015 and 2016), increased in 2017 but fell again in 2018. The long-term pattern of reduced average weight is probably due to increasing fishing mortality, resulting from the increasing number of purse seine sets. Any continued decline in average length is a concern.

This stock assessment presents a number of uncertainties. Overall, considering that there is no concern for biomass, that skipjack is less susceptible to overfishing that other tropical tunas, and that the scientific assessment cannot provide clear indications of overfishing, MCS considers that there is currently no concern for biomass or fishing pressure.

As skipjack and bigeye tuna stocks have similar characteristics, skipjack status can be inferred from bigeye status, as long as bigeye fishing mortality is below the MSY level. The 2018 assessment of bigeye indicates that the stock is subject to overfishing, so skipjack status cannot be inferred from bigeye status. The large-scale tagging program in the EPO, which began in 2019 and will run until 2023, is critical to obtain an assessment of this stock.

Discards of skipjack at sea have decreased each year, from 8% in 2004 to a low of less than 1% in 2017, averaging about 3% of the total catch of the species.

Management

Criterion score: 0.75 info

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.

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. Further evaluation of this HCR and alternatives will be conducted, so that a permanent HCR can be adopted. In 2002, purse seine fleet capacity (defined by the well volume of the boats) was frozen. 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: fleet capacity in 2017 was estimated to be about 6.7% greater than the previous three-year average. Management measures were updated accordingly, in line with recommendations: the 62-day closure for large purse seiners was extended to 72 days annually until 2020. The scientific committee considers it essential that fleet capacity does not increase further. In 2019, skipjack, yellowfin and bigeye assessments were too uncertain to produce values for fishing mortality, and stock status indicators were 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 per-vessel limits on the number of FADs that can be active at any one time (between 70 and 450, depending on vessel size) and regular reporting on FAD activity is required. However, it is considered to be impractical to limit FAD purse seining alone, as accurate real-time monitoring of FAD versus non-FAD sets is challenging. Instead the combined number of purse seine sets (FAD and non-FAD) is recommended to 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 current FAD limits are considered to be arbitrary and too high, and should be reduced by 30%.

Until 2020, there is a 30-day closure of an area known as the “Corralito” (west of the Galapagos Islands, where catch rates of small bigeye are high) to the purse-seine fishery for yellowfin, bigeye, and skipjack tuna.

A requirement to retain and land all bigeye, skipjack, and yellowfin tuna caught by purse seine has been extended until 2020, although the degree of enforcement regime may vary depending on the country or authority.

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. 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 commonly an industrial scale fishery used to catch tuna destined for canneries. These fisheries target smaller fish that aggregate close to the surface, whereas longliners target larger fish that inhabit deeper waters. Many juvenile fish are often caught in purse seine fisheries and the method can also be associated with bycatch of vulnerable species, in particular sharks. In the EPO, the bycatch of sharks comprises a small proportion of the total catch of tuna, but as the volume of tuna caught is high, the catch of sharks is still significant.

FAD-associated purse seining generally encounters higher bycatch rates compared with sets on free-schools, and higher proportions of juvenile tuna. Most of the bigeye purse-seine catch is produced by the fishery on floating-objects which targets skipjack tuna. Bigeye tuna is considered to be in an overfished state, with overfishing occurring, and fishing morality needs to be reduced on this species. It’s unknown if the widespread use of FADs has other impacts such as on the natural species composition of tuna schools, migratory patterns, growth rates and predation rates of affected pelagic species. Poorly designed FADs can also entangle animals like sharks and turtles.

Bycatch mitigation measures such as sorting grids are in place to reduce mortality of turtles, sharks and non-target species in general. From Jan 2015, all purse seiners using FADs in the EPO must record and report to the authorities details relating to the FAD design, deployment, catch and bycatch summaries for each set. Additionally, FAD design is required to be non-entangling so as to minimise interaction with turtles and sharks and is encouraged to be made from biodegradable materials. Further restrictions to reduce the entanglement of sharks, sea turtles or any other species come into force in January 2019. Vessels are prohibited from knowingly setting a purse seine around tuna schools associated with a live whale shark and if a whale shark is incidentally encircled, all reasonable steps must be taken to ensure its safe release. Whale shark interactions are not common in this fishery. Details of the interaction must be recorded, as with all other sharks and turtles. Permissible sharks are to be fully utilized and no more than 5% of fins to total shark weight can be retained; landing oceanic whitetip, silky sharks and mobula rays is prohibited and vessels must not fish in silky shark pupping areas. 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. Mobulid rays are among the bycatches of the tropical tuna purse-seine fishery, and are of special concern because of their low reproductive rates. Purse seining in the eastern Pacific Ocean catches an average of 1,500 mobula rays per year, mostly in dolphin and free-schooling sets. For other shark species, mainly silky, oceanic whitetip, hammerhead, and mako, catches are generally greatest in sets on floating objects, followed by unassociated sets and, at a much lower level, dolphin sets. In 2018, all forms of purse seining combined caught 505 tonnes of sharks. Longlining caught 13,680t. The scientific committee 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. There is 100% observer coverage on large purse seiners in the EPO so the data coming from these fleets should be useful and of high quality. Data from small purse seiners is very poor and 20% observer coverage is recommended for them as well.

Alternatives

Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.

Anchovy, anchovies
Arctic char
Herring or sild
Mackerel
Salmon, Atlantic (Farmed)
Salmon, Chum, Keta, Calico or Dog salmon
Salmon, Pink, Spring , humpback
Salmon, Sockeye , Red Salmon, Bluebacks, Redfish
Swordfish
Trout, Rainbow
Tuna, albacore
Tuna, skipjack
Tuna, yellowfin

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 03.12.2019].

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].

Hall, M., Lezama-Ochoa, N., and Roman, M., 2019. Mobulid rays. 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_Mobulids%20rays.pdf [Accessed on 03.12.2019].

IATTC, 2019. Inter-American Tropical Tuna Commission: Active IATTC and AIDCP Resolutions and Recommendations. Available at https://www.iattc.org/ResolutionsActiveENG.htm [Accessed on 02.12.2019].

IATTC, 2019. Report on the tuna fishery, stocks, and ecosystem in the Eastern Pacific Ocean in 2018, Document IATTC-94-01 presented to the Inter-American Tropical Tuna Commission 94th Meeting, 22-26 July 2019, Bilbao, Spain. 125pp. Available at https://www.iattc.org/Meetings/Meetings2019/IATTC-94/Docs/_English/IATTC-94-01_The%20tuna%20fishery,%20stocks,%20and%20ecosystem%20in%20the%20Eastern%20Pacific%20Ocean%20in%202018.pdf [Accessed on 02.12.2019].

IATTC, 2019. The tuna fishery in the Eastern Pacific Ocean in 2018 (revised). Inter-American Tropical Tuna Commission Scientific Advisory Committee Tenth Meeting, 13-17 May 2019, San Diego, California (USA). 49pp. Available at https://www.iattc.org/Meetings/Meetings2019/SAC-10/Docs/_English/SAC-10-03-REV-14-May-19_The%20tuna%20fishery%20in%20the%20EPO%20in%202018.pdf [Accessed on 03.12.2019].

IATTC, 2019. Staff recommendations for management and data collection, 2019. Document IATTC-94-03 presented to the Inter-American Tropical Tuna Commission 94th Meeting, 22-26 July 2019, Bilbao, Spain. Available at https://www.iattc.org/Meetings/Meetings2019/IATTC-94/Docs/_English/IATTC-94-03_Conservation%20recommendations%20by%20the%20Commission%20staff.pdf [Accessed on 03.12.2019].

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].

Lopez, J., Lennert-Cody, C. E., Maunder, M. N., Xu, H., Brodie, S., Jacox, M., Hartog, J., 2019. Developing alternative conservation measures for bigeye tuna in the eastern pacific ocean: a dynamic ocean management approach. Document SAC-10 INF-D presented to the Inter-American Tropical Tuna Commission Scientific Advisory Committee Tenth Meeting, 13-17 May 2019, San Diego, California, USA. 24pp. Available at https://www.iattc.org/Meetings/Meetings2019/SAC-10/INF/_English/SAC-10-INF-D_Bigeye%20tuna%20Dynamic%20Ocean%20Management.pdf [Accessed on 04.12.2019].

ISSF, 2019. Status of the world fisheries for tuna. Oct. 2019. ISSF Technical Report 2019-12. International Seafood Sustainability Foundation, Washington, D.C., USA. Available at https://iss-foundation.org/knowledge-tools/technical-and-meeting-reports/download-info/issf-2019-12-status-of-the-world-fisheries-for-tuna-october-2019/ [Accessed on 26.11.2019].

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].