Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Gill or fixed net
Capture area — Indian Ocean: Western (FAO 51), Eastern ( FAO 57)
Stock area — Indian Ocean
Stock detail — All Areas
Picture of Tuna, skipjack

Sustainability rating five info

Sustainability overview

Updated: November 2020

Skipjack in the Indian Ocean is currently not in an overfished state, and not subject to overfishing. However, recent catches have been well above the catch limits and this lack of control is concerning. A harvest control rule is in place for this fishery, but management measures are clearly not controlling fishing pressure on the stock. There are significant issues with monitoring and compliance in most fisheries that are overseen by the Indian Ocean Tuna Commission (IOTC). This reduces the accuracy of stock assessments, the effectiveness of management measures, and the likelihood of maintaining the fisheries at a sustainable level. Observer coverage, which could improve monitoring, is very low, at just 5%. Recommendations are for 20%. Therefore, MCS considers Indian Ocean tuna and swordfish fisheries to be poorly managed and requiring considerable improvement. An alarming 20% of skipjack catch is made by gillnets, a gear expected to have high bycatch rates. They can be 7 km long and are known for extremely high bycatch including turtles, whales, dolphins, whale sharks, mobulids, requiem sharks and sunfish. Monitoring and reporting in these fisheries in the Indian Ocean is extremely deficient, and there are few mitigation measures in place. A critical fail is applied to capture method impacts due to bycatch concerns, resulting in a default red rating.

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

Indian Ocean skipjack is not overfished and not subject to overfishing, despite recent large catches tht exceeded the catch limits.

This stock is managed by the Indian Ocean Tuna Commission (IOTC). A new stock assessment was carried out in 2020, using data up to 2019. Catches for Indian Ocean skipjack gradually increased from the 1950s to the 1980s, staying below 100,000 tonnes. They then sharply increased to over 600,000t in 2006, before dropping to around 350,000t in 2012. Another peak followed, again reaching 600,000t in 2018. These dramatic fluctuations in catches correspond with significant drops in the biomass of the spawning portion of the stock (spawning biomass, SB). SB is estimated to have dropped from very high levels in the 1980s to below target levels in the early 2010s. It has since recovered, and is estimated to be 11% above the target level, which is a spawning stock size of 40% of unfished levels (SSB 2019:SSB 40%SSB0 = 1.11). Meanwhile, the exploitation rate (E) has contuously increased, exceeding target levels in the mid-2010s and only recently falling just below them again. In 2019, E was 92% of target levels, which is an exploitation rate consistent with keeping the stock at 40% of unfished levels (E 2019:E 40%SSB0 = 0.92). The new target limit according to the 2020 assessment is 536,000t, an increase on the preivous assessment, which indicated a limit of 510,100t. Catches in 2018 and 2019 (547,248 t) exceeded this and the 2018 -2020 TAC (470,029t), which is of concern for future management of this stock.

Due to its specific life history attributes, skipjack can respond quickly to ambient foraging conditions driven by ocean productivity, which seem to have been favourable in recent years. Environmental indicators should be closely monitored to inform on the potential increase/decrease of stock productivity. The reduction since 2006 has been partially attributed to piracy in the western Indian Ocean (especially in waters near Somalia, Kenya, Tanzania and the Maldives).

Management

Skipjack in the Indian Ocean is currently not in an overfished state, and not subject to overfishing. However, recent catches have been well above the catch limits and this lack of control is concerning. There are significant issues with monitoring and compliance in most fisheries that are overseen by the Indian Ocean Tuna Commission (IOTC). This reduces the accuracy of stock assessments, the effectiveness of management measures, and the likelihood of maintaining the fisheries at a sustainable level. Observer coverage, which could improve monitoring, is very low, at just 5%. Recommendations are for 20%. Therefore, MCS considers Indian Ocean tuna and swordfish fisheries to be poorly managed and requiring considerable improvement.

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; for this stock it is the Indian Ocean Tuna Commission (IOTC). There are five main tuna RFMOs worldwide and it is their responsibility to carry out data collection, scientific monitoring and management of these fisheries. 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.

Monitoring and compliance with management measures in the IOTC region is generally poor, and MCS is particularly concerned about the impact this is having on a number of species. Some countries repeatedly fail to report catch data to the commission annually. In 2018 IOTC introduced a new measure aimed at improving reporting on catch and bycatch, including prohibiting a country from retaining a species if they fail to report catches for it. However, in 2020 the scientific committee reported that data reporting issues persist.

IOTC has set targets and thresholds for fishing effort and spawning stock biomass for the species it manages, which is positive. Even more encouragingly, a Harvest Control Rule (HCR) for skipjack came into force in 2017, with a target of maintaining the stock at or above 40% of unfished levels. Catch limits are based on stock assessments, carried out every 3 years. The Total Allowable Catch for 2018-2020, based on the 2017 stock assessment, is 470,029 t. Catches in 2018 (600,000t) and 2019 (provisionally 547,248t) have significantly exceeded it. This lack of control and enforcement is of significant concern, and undermines the potential of a Harvest Control Rule to keep the stock at sustainable levels. The scientific committee has suggested that the rebuilding plan for yellowfin and associated restrictions has displaced activity onto purse seines with fish aggregating devices, which has led to an associated increase in skipjack catches. Skipjack catches by the purse seine fishery increased by 43% from 2017 to 2018.

On average from 2015-2019, purse seining accounted for around 53% of skipjack catches: 42% using Fish Aggregating Devices (FADs) and 2.4% on free-schooling fish. The maximum number of drifting FADs that can be in use at any one time by each purse seiner has been steadily reduced from 550 in 2015 to 300 in 2019, and the maximum that can be acquired each year reduced from 1100 in 2015, to 500 in 2019. Countries that use FADs must report regularly to the Commission and submit FAD management plans outlining how they will minimise mortality of juvenile yellowfin and bigeye tuna and vulnerable non-target species such as sharks, turtles and rays.

Vessel capacity and tonnage was frozen to 2007 levels for vessels over 24m, or vessels under this length operating in international waters. This measure expired in 2018, and IOTC reverted to previous legislation which froze capacity and tonnage to 2003 levels. This legislation is very generic, applying across all fleets, and would be better replaced by spatial and temporal closures and quota allocation. There also appear to be concerns that the freeze has not been well enforced thus far.

In 2016 IOTC introduced a number of resolutions to improve the poor compliance with existing management measures, e.g. observer coverage, catch and effort reporting, support for countries to implement measures. However, mandatory observer coverage is very low, at just 5% for all vessels over 24m or under 24m and fishing outside of their Exclusive Economic Zone (EEZ). A number of countries fail to meet the 5% threshold. In general, 20% is scientifically recommended to ensure adequate monitoring of catch and bycatch. In 2019 a proposal was put forward to increase coverage to at least 20%, but consensus could not be reached.

Other IOTC conservation and management measures of note include:
A ban on the discarding of bigeye, yellowfin and skipjack tunas by purse seine vessels which from 2018 will extend to non-target species such as other tunas and billfish.
A ban on the use of aircraft and unmanned aerial vehicles as fishing aids, which significantly contribute to fishing effort by helping to detect fish.
A ban on surface or submerged artificial lights for the purpose of aggregating tuna and tuna-like species beyond territorial waters.
In 2012 IOTC banned the use of driftnets on the high seas. In 2022 this will be extended to the entire IOTC area (i.e. within countries’ EEZs as well).
To help address IUU, the IOTC maintains an active vessel register and an IUU Vessel List and prohibits transhipments for large scale vessels at sea unless they are pre-approved, monitored by an observer and the vessel uses a Vessel Monitoring System (VMS).

Capture Information

Criterion score: Critical Fail info

An alarming 20% of skipjack catch is made by gillnets, a gear expected to have high bycatch rates. Whilst it is known that vessels from Iran and Sri Lanka have been using gillnets on the high seas in recent years, reaching as far as the Mozambique Channel, the activities of these fleets are poorly understood, as no information about catches and effort has not been available. As such a large amount of skipjack is caught in gillnet fisheries in many different countries, it is important for the commercial supply chain to have robust traceability systems in place to ensure that gillnet caught or Illegal, Unreported and Unregulated seafood (IUU) doesn’t end up mixed in with skipjack from more sustainable sources.

Gillnets being used for catching tuna and tuna like species can be 7km long and are known for extremely high bycatch including turtles, whales, dolphins, whale sharks, mobulids, requiem sharks and sunfish. Monitoring and reporting in these fisheries in the Indian Ocean is extremely deficient, and there are few mitigation measures in place. The IOTC prohibits fishing with gillnets larger than 2.5 kilometres in the high seas, and from 2022 in EEZs (although Pakistan, a major part of the gillnet fleet, has objected to the latter and is exempt). Despite these restrictions, the Indian Ocean is one of the few regions in the world where gillnetting is being increasingly carried out.

Sharks and rays: Better data reporting is needed, as impacts and population trends are not well understood. Piracy displaced longlining into the southern and eastern Indian Ocean, and there could be localised depletion of sharks here. Full utilisation of sharks is required (i.e. no fin removal), unwanted sharks must be released live wherever possible and shark catches must be reported annually. Countries must develop conservation and management measures for vulnerable shark species. Transshipment of oceanic whitetips and threshers is prohibited. A number of countries are banning the retention of oceanic whitetip, in accordance with IOTC resolutions, but it is too early to evaluate the impact of this. In 2019 the first resolution for any ray species in the IOTC area of competence was brought in. It protects mobulid rays, which are declining across the Indian Ocean. Targeted fishing, retention, transhipping, landing, selling, or storage of mobulid rays is prohibited, with exceptions made for accidental catch by artisanal fishing until 2022. The status of shark species in 2020 were:
Blue shark is not currently overfished or subject to overfishing, but will become so if current catches continue. It is fairly resilient, for a shark species, and is targeted by longliners in several areas as well as bycaught by swordfish longliners. Management measures could be introduced in 2021.
Oceanic whitetip is Critically Endangered, and mainly caught by trolling and gillnetting. There is not enough data to assess the stock but it could be declining.
Scalloped hammerhead is endangered in the western Indian Ocean, caught by a range of gears. It is less susceptible to being caught by longline than other sharks.
Shortfin mako is endangered and considered the most vulnerable Indian Ocean shark species as it is very susceptible to longlining, less so to purse seining. Trends are conflicting, but as it has been placed on CITES Appendix II, future landings could be affected.
Silky shark is Vulnerable, and highly susceptible to longline and purse seine. Abundance could be declining.
Bigeye thresher is Vulnerable and commonly caught as bycatch by longliners. Catches haven’t been reported since 2012. Pelagic thresher is Endangered, and highly susceptible to purse seining. It is commonly caught as bycatch by longliners. Most threshers die after being hooked, even if released. Therefore the ban on retaining them, and promoting live-release, is probably not effective at protecting them.

Turtles: The status of all turtle species in the Indian Ocean is concerning, and interactions are severely underreported. The last specific regulations to protect turtles were passed in 2012. Turtles must be released wherever possible and countries are requested to research other mitigation techniques. Longliners must carry cutters or de-hookers to aid with this but gear modification, such as circle hooks, is not required. Gillnetting is the biggest concern for turtles, with estimates ranging from 11,000-52,000 individuals being caught annually. Longlining in the southwest may also have an impact on population levels. Turtles can also be entangled by Fish Aggregating Devices used by purse seiners. Estimates of catch by longline and purse seine ranges from 250-3,500 individuals. Green turtles are mostly caught by gillnets, while loggerhead, hawksbill, leatherback and olive ridley are caught by various gears depending on the season. The scientific committee advises that maintaining or increasing fishing effort in the Indian Ocean without appropriate measures in place will likely result in further population declines. It recommends that appropriate mechanisms are developed to ensure compliance with data collection and reporting requirements.

Seabirds: Seabird bycatch is mainly of concern in longline fisheries, fishing south of 25 degrees South. While the status of seabirds is affected by a range of factors such as degradation of nesting habitats and targeted harvesting of eggs, for albatrosses and large petrels, fisheries bycatch is generally considered to be the primary threat. Several Endangered and Critically Endangered species are being caught, including the Critically Endangered Tristan albatross. As with most tuna RFMOs, the IOTC requires two seabird bycatch mitigation measures from a list of three options (weighted branch line, bird scaring lines, and night setting), but recommended best practice is for these three measures to be applied simultaneously. Monitoring and reporting is deficient, and there has not been enough information available to fully review the effectiveness of the applied mitigation measures.

Marine mammals: Very little effort has gone into monitoring and mitigating the bycatch and entanglement of cetaceans. Most recorded interactions are from gillnets. Longline is also of concern as cetaceans could be attracted by the fish caught on the line. Purse seine can encircle or entangle the animals, although interactions are thought to be low. It is illegal to intentionally set a purse seine net around a cetacean if the animal is sighted prior to the commencement of the set. In 2020, it was noted that there are tuna-dolphin associations for yellowfin tuna. This is where fishers wait for dolphins to encircle a school of tuna, and then try to catch the tuna, e.g. with nets. The dolphins are not targeted, but can be caught as bycatch. This association appears to be rather widespread around the Indian Ocean, and is used by coastal country fishermen in Maldives, Sri Lanka, Oman and elsewhere to target yellowfin tuna.

Several countries have failed to implement national plans of action (NPOAs) for sharks, seabirds and turtles as required (although the shark plan is not binding in India as they have objected to the measure). In 2020, of the 34 members of IOTC, 16 countries had completed NPOAs for sharks. Just 7 had plans for seabirds, although 8 countries report low or no interaction because they don’t use longline or don’t fish south of 25 degrees S. 11 countries had plans for turtles. Click here to see which countries had and had not fully implemented NPOAs.

Mandatory observer coverage is very low, at just 5% for all vessels over 24m or under 24m and fishing outside of their Exclusive Economic Zone (EEZ). A number of countries fail to meet the 5% threshold. In general, 20% is scientifically recommended to ensure adequate monitoring of catch and bycatch. In 2019 a proposal was put forward to increase coverage to at least 20%, but consensus could not be reached.

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].

Aranda, M., 2017. Description of tuna gillnet capacity and bycatch in the IOTC Convention Area, IOTC-2017-WPEB13-18, for the 13th Working Party on Ecosystems and Bycatch for the Indian Ocean Tuna Commission, 4-8 September 2017, San Sebastian, Spain. 28pp. Available at http://www.iotc.org/meetings/13th-working-party-ecosystems-and-bycatch-wpeb13 [Accessed 23.11.2017].

Criquet, G., Stokes, K. and Halim, A., 2020. Marine Stewardship Council (MSC) 2nd Surveillance Report: Maldives pole & line skipjack tuna, September 2020. Prepared by SAI Global on behalf of Maldives Seafood Processors & Exporters Association (MSPEA). 54pp. Available at https://fisheries.msc.org/en/fisheries/maldives-pole-line-skipjack-tuna/@@assessments [Accessed on 07.12.2020].

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Fu, D. 2020. Preliminary Indian Ocean Skipjack Tuna Stock Assessment 1950-2019 (Stock Synthesis). IOTC–2020–WPTT22–10. 57pp. Available at https://iotc.org/sites/default/files/documents/2020/10/IOTC-2020-WPTT22AS-10_Rev1.pdf [Accessed on 04.12.2020].

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].



IOTC, 2018. Report of the 22nd Session of the Indian Ocean Tuna Commission, IOTC-2018-S22-R[E]. 21-25 May 2018, Bangkok, Thailand, 144pp. Available at https://iotc.org/documents/report-22nd-session-indian-ocean-tuna-commission [Accessed on 28.11.2019].

IOTC, 2019. Report for the 23rd session of the Indian Ocean Tuna Commission, IOTC-2019-S23-R_rev1[E], 17-21 June 2019, Hyderabad, India. Available at https://iotc.org/sites/default/files/documents/2019/10/IOTC-2019-S23-RE_Rev1_FINAL.pdf [Accessed on 26.11.2019].

IOTC, 2019. On a regional observer scheme. Paper IOTC-2019-S23-PropJ[E] submitted by the European Union to the 23rd session of the Indian Ocean Tuna Commission, 17-21 June 2019, Hyderabad, India. 5pp. Available at https://iotc.org/documents/regional-observer-scheme-eu [Accessed on 27.11.2019].

IOTC, 2019. Compendium of Active Conservation and Management Measures for the Indian Ocean Tuna Commission, 29 October 2019. Available at https://iotc.org/sites/default/files/documents/compliance/cmm/IOTC_-_Compendium_of_ACTIVE_CMMs_29_October_2019_designed.pdf [Accessed on 04.12.2020].

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