Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Pole & line
Capture area — Indian Ocean, Western (FAO 51) and Eastern ( FAO 57)
Stock area — All Areas
Stock detail

All Areas


Picture of Tuna, skipjack

Sustainability rating two info

Sustainability overview

The most recent assessment for Indian Ocean skipjack tuna was carried out in 2017 and indicated that the stock was not overfished nor subject to overfishing but great uncertainty noted. A harvest control rule and TAC are now in place for this fishery. However, catches have recently begun to increase, with the 2012-2016 average at 407,456 t and the provisional 2017 catch at 524,282 t: above the proxy for MSY of 510,100 t. The 2018 -2020 TAC is 470,029 t, so if the high catch of 2017 were to continue it would be cause for concern. The stock has declined due to lower than expected recruitment in the recent period and it is unclear if recruitment will return to the expected levels in the near future. Some countries in the IOTC do not report fishery data which is important for stock assessment and management and in 2018, the IOTC introduced a new measure aimed at improving reporting on direct and incidental catches, including prohibiting a country from retaining a species if they fail to report catches for that species. About 20% of skipjack catches in the Indian Ocean come from pole & line fisheries. Pole & line fishing is very selective but does contribute to catches of juvenile yellowfin and bigeye, and does rely on a substantial amount of small live fish for bait. The total catch of bait fish is relatively low compared to targeted fisheries and is unlikely to overexploit these stocks, but could have implications for local availability so should be monitored.

The Maldives fishery is certified by the Marine Stewardship Council (MSC) as a well managed fishery. Some other pole & line fleets are also in a Fishery Improvement Project (FIP) which is making progress on improving elements of the fishery. More info about the FIP 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

All Areas

Stock information

Skipjack and other tuna stocks in the Indian Ocean are assessed by IOTC - the Indian Ocean Tuna Commission. Catches of skipjack in the Indian Ocean increased dramatically from 50,000t in 1980 to over 600,000t in 2006, coinciding with the widespread use of Fish Aggregation Devices (FADs) in the purse seine fisheries. After that, catches were relatively stable at around 400,000t. 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).

The most recent assessment for Indian Ocean skipjack tuna was carried out in 2017, which differs from the previous (2014 and 2011) assessments owing to improvements to the model and inclusion of new data. There remains considerable uncertainty in the assessment, but as with the previous assessments the skipjack tuna stock is determined to be not overfished (spawning stock biomass is at the target level of 40% of unexploited levels) and is not subject to overfishing. However, catches have recently begun to increase, with the 2012-2016 average at 407,456 t and the provisional 2017 catch at 524,282 t - above the proxy for FMSY of 510,100 t. The 2018 -2020 TAC is 470,029 t, so if the high catch of 2017 were to continue it would be cause for concern. It is worth noting that the stock has declined due to lower than expected recruitment in the recent period and it is unclear if recruitment will return to the expected levels in the near future.

Given the current status of the fishery and assuming that catch does not exceed recommended levels, it would be expected that the stock would fluctuate around the target level. Fluctuations in catch per unit effort, mainly for the purse seine, coincide with changing environmental conditions. Due to its specific life traits, skipjack can respond quickly to foraging conditions driven by ocean productivity. The scientific committee recommends that environmental indicators should be closely monitored to inform on the potential increase/decrease of stock productivity.

Management

Criterion score: 0.25 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; 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.

There are persistent failures by some countries to report to the commission annually, including reporting catch data, and other issues with lack of data and poor quality data persist. In 2018 IOTC introduced a new measure aimed at improving reporting on direct and incidental catches, including prohibiting a country from retaining a species if they fail to report catches for that species.

IOTC has set targets and thresholds for fishing effort and spawning stock biomass for the species it manages. A Harvest Control Rule (HCR) for skipjack came into force in 2017, with a target of maintaining the spawning stock at or above 40% of its unfished biomass. It requires stock assessments every 3 years and bases catch limits on those assessments. It also states that maximum Total Allowable Catch (TAC) should never exceed 900,000 t (the upper estimate of MSY based on the 2014 assessment). The TAC for 2018-2020, based on the 2017 stock assessment, is 470,029 t. 2016 catches were below this level.

Other IOTC conservation and management measures of note include:
A ban on the discarding of bigeye, yellowfin and skipjack tunas by purse seine vessels, as well as of non target species such as other tunas and billfish.
A ban on the use of aircrafts 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).
Regarding the use of drifting Fish Aggregation Devices (FADs): The maximum number of drifting FADs that can be in use at any one time by each purse seiner was reduced from 550 in 2015 to 425 in 2016 and 350 in 2017. The maximum that can be acquired each year was reduced from 1100 in 2015 to 850 in 2016 and 500 in 2017. 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. To reduce the entanglement of sharks, marine turtles or any other species, the design and deployment of FADs must be based on certain principles: The surface of the FAD should not be covered, or only covered with non-meshed material; If a sub-surface component is used, it should not be made from netting but from non-meshed materials such as ropes or canvas sheets; To reduce the amount of synthetic marine debris, the use of natural or biodegradable materials should be promoted. From 2016, each FAD must be marked with a unique identification number.
There is a freeze on capacity to 2006 levels which extends to vessels greater than 24m in length, or vessels under this length operating in international waters. This is to be reviewed in 2018.
5% regional observer coverage is required for all vessels over 24m and for vessels under 24m fishing outside of their Exclusive Economic Zone (EEZ).
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).

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.

Capture Information

Criterion score: 0.25 info

In 2016 around 20% of skipjack catches in the Indian Ocean were from pole and line fisheries, almost all of it from the Maldives. In recent years, pole and line catches for skipjack have decreased corresponding with the development of the handline fishery for the larger yellowfin tuna.

Pole and line fishing consists of a bamboo or plastic pole, 10 to 15 feet in length, with a line and a feathered barbless hook attached to the smaller end of the pole, capable of handling a fish weighing below 23kg. Bycatch is relatively low in these fisheries, yet can be greater when used in conjunction with Fish Aggregation Devices (FADs). Pole and line fishing is a very selective method of fishing, yet it does depends on significant quantities of bait fish to attract the tuna. In the Maldivian targeted skipjack pole and line fishery, for example, it has been estimated that for each tonne of bait fish, roughly seven tonnes of skipjack are caught. In this fishery, the primary bait fish used is silver sprat. Whilst this species is a small and relatively resilient to overfishing, there is a need to ascertain what impact their use as bait may have on the stock and to develop some basic management measures.

References

Fishery Progress, 2018. Fishery Improvement Project Directory. Available at https://fisheryprogress.org/ [Accessed on 05.12.2018].

IOTC, 2017. Report of the 13th Working Party on Ecosystems and Bycatch, IOTC-2017-WPEB13-R, for the Indian Ocean Tuna Commission, 4-8 September 2017, San Sebastian, Spain. 124pp. Available at http://www.iotc.org/meetings/13th-working-party-ecosystems-and-bycatch-wpeb13 [Accessed 21.11.2017].

IOTC, 2018. Compendium of Active Conservation and Management Measures for the Indian Ocean Tuna Commission, 04 October 2018. Avaiable at http://www.iotc.org/cmms [Accessed on 6.12.2018].

IOTC, 2018. Draft Resource Stock Status Summary Skipjack Tuna, Status of the Indian Ocean skipjack tuna (SKJ: Katsuwonus pelamis) resource, IOTC-2018-SC21-ES03 for the 21st Meeting of the Scientifc Committee of the Indian Ocean Tuna Commission, 3-7 December 2018, Mahe, Seychelles. 3 pp. Available at http://www.iotc.org/meetings/21st-scientific-committee-sc21 [Accessed on 04.12.2018].

IOTC, 2018. Outcomes of the 22nd Session of the Indian Ocean Tuna Commission, IOTC-2018-SC21-16 [E], 21-25 May 2018, Bangkok, Thailand. 4 pp. Available at http://www.iotc.org/meetings/22nd-session-indian-ocean-tuna-commission-s22 [Accessed on 04.12.2-18].

IOTC, 2018. Report of the 22nd Session of the Indian Ocean Tuna Commission, IOTC-2018-S22-R[E], 21-25 May 2018, Bangkok, Thailand. 144 pp. Available at http://www.iotc.org/meetings/22nd-session-indian-ocean-tuna-commission-s22 [Accessed on 04.12.2-18].

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

ISSF, 2018. Status of the world fisheries for tuna: October 2018. ISSF Technical Report 2018-21. International Seafood Sustainability Foundation, Washington, D.C., USA. 103 pp. Available at: https://iss-foundation.org/about-tuna/status-of-the-stocks/ [Accessed on 06.12.2018].