Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Pole & line
Capture area — Western & Central Pacific - WCPO (FAO 61,71,77)
Stock area — Western and Central Pacific
Stock detail

All Areas


Picture of Tuna, skipjack

Sustainability rating two info

Sustainability overview

The latest stock assessment was undertaken in 2016 and results were very similar to previous assessments, indicating that the stock is not overfished (Spawning Biomass, SB, at 2.56 Bmsy) nor being subject to overfishing (Fishing mortality, F, at 0.45 Fmsy). In 2018, the Western and Central Pacific Fisheries Commission (WCPFC) adopted a bridging measure to manage bigeye, yellowfin and skipjack until harvest strategies are in place or February 2021. As part of this, the average spawning biomass for skipjack is to be maintained at the interim target of 50% of unfished levels (about current levels). There is no Total Allowable Catch (TAC) set for this stock, but as skipjack is caught alongside bigeye and yellowfin, primarily in purse seine fisheries, the range of measures and capture method impacts listed for bigeye also apply to skipjack. About 8% of the catch is taken in pole & line fisheries. These are very selective but do rely on a substantial amount of small live fish for bait. The total catch of bait fish in pole & line fisheries is generally considered low compared to targeted fisheries for these species and is unlikely to overexploit these stocks, but could have implications for local availability.

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

Stock Area

Western and Central Pacific

Stock information

The Western and Central Pacific Ocean (WCPO) skipjack stock supports the largest tuna fishery in the World, accounting for approximately 38% of worldwide tuna landings. It is managed and assessed by the Western and Central Pacific Fisheries Commission (WCPFC).

Skipjack tuna catches in the WCPO increased steadily from 1970 onwards, roughly doubling during the 1980s. After stabilising at around 1,000,000t during the early 1990s, they increased to between 1.5 and 2 million t from 2007 and a record catch of just over 2 million t was taken in 2014. The increase in fishing mortality since the 1980s has been due to the increase of catches of both juvenile and adult fish from both associated purse seine sets and the mixed gear fisheries in the Philippines and Indonesia. Biomass also increased from the early 1980’s, resulting from higher recruitments, then fluctuated and declined slightly up until 2012. Since then there appears to have been a strong increase in spawning biomass, peaking in 2013/2014 at levels just below the 1980s peaks.

The total skipjack catch in 2016 (1,816,762 t) was the fourth highest recorded, nearly 160,000 mt less than the record in 2014 (1,977,019 mt). It was comparable to that in 2015 and a 2% increase over 2011-2015. The latest stock assessment was undertaken in 2016 and results were very similar to previous assessments, indicating that the stock is not overfished (Spawning Biomass, SB, at 2.56 Bmsy) nor being subject to overfishing (Fishing mortality, F, at 0.45 Fmsy). Recent levels of spawning biomass are well above the level that will support MSY, and while there has been a steady depletion of the stock over most of the assessment period, the stock is still estimated to be healthy, and is estimated to have been at approximately 50% of unfished levels for the past decade: well above the limit reference point of 20%.

Under recent fishery conditions (2016), the skipjack stock is initially projected to decrease for a short period and then to increase as recent relatively high recruitments move through the stock (predicted F2018/FMSY = 0.37, and SB2018/SBF=0 = 0.47).

The scientific committee advise 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. Currently, pole and line CPUE is the major indicator of abundance for assessment purposes, which in 2017 represented around 10% of the catch and continues to shrink geographically.

Management

Criterion score: 0.5 info

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.

WCPFC has put in place a lower limit for the spawning biomass of bigeye, skipjack, and yellowfin tuna of 20 percent of unfished levels (SB/SBF=0, aka spawning biomass depletion ratio), below which the stock should not fall. For skipjack there is also an interim target of 50 percent of unfished levels, which was adopted in 2015 and has been reached. The scientific committee recommends reducing fishing mortality on juvenile bigeye and yellowfin in the tropics, through preventing increases in overall fishing mortality, until targets for these two stocks can be agreed. The commission is looking to establish harvest strategies for key fisheries and stocks but has not yet completed this work and so, as of January 2018, a bridging measure is in force to manage bigeye, yellowfin and skipjack - the measure lasts until harvest strategies are in place or until February 2021. As part of this, spawning biomass depletion ratios for bigeye and yellowfin are to be maintained at recent levels (the average from 2012-2015) and skipjack at 50 percent. The bridging measure includes a number of new measures and consolidates some pre-existing ones, and is outlined below.

In the tropical region, between 20 degrees North and 20 degrees South, the following applies:
The use and deployment of FADs is prohibited 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. In order not to undermine the effectiveness of this, countries cannot transfer effort into areas outside of this region.
To create an incentive to reduce the non-intentional capture of juvenile fish, to discourage waste and to encourage an efficient utilization of fishery resources, purse seiners must retain on board and then land or transship at port all bigeye, skipjack, and yellowfin tuna (also applies to national waters).
All purse seine vessels operating on the high seas or within national waters in this region must carry an observer. This also applies to purse seiners anywhere in the convention area fishing in waters under multiple countries’ jurisdiction or moving between the high seas and national waters.
The number and capacity of large (over 24m) purse seiners and longliners (with freezing capacity and ice-chilled) operating in this area is frozen to 2016 levels (excluding SIDs and Indonesia).

Other measures that apply to the wider convention area:
The number of drifting FADs with activated instrumented buoys deployed at any one time is limited to 350 per purse seine vessel.
Catch and/or effort limits apply for purse seining within national waters (both the type of limit and the amount vary by country).
There are country-specific limits on longline bigeye catch, and by 2020 hard limits for bigeye and a framework to allocate them amongst countries shall be developed.
Catches by other commercial tuna fisheries for bigeye, yellowfin or skipjack tuna (excluding those taking less than 2,000 tonnes) shall not exceed either the average level for the period 2001-2004 or the level of 2004.

More generally:
There is a requirement to submit FAD management plans, including information on strategies used to implement closures and other measures for reducing mortality of juvenile bigeye. A number of aspects in the bridging measure have been brought forward from previous management measures, and 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.
Observer coverage on purse seiners is poor in areas not specified in the bridging measure and only 5% coverage is required on longliners greater than 20m in length. 20% is considered to be the minimum to be effective.
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: 0.25 info

The Western and Central Pacific Ocean (WCPO) supports the largest skipjack tuna fishery in the world. Economic factors and technical advances in the purse seine fishery have seen a gradual decline in the number of vessels in the pole and line fishery, which now accounts for approximately 8% of the skipjack catch. Pole and line fishing is a very labour intensive yet selective method of fishing, having little bycatch, yet considerable amounts of bait fish are used in these fisheries to attract the skipjack. Whilst bait fish are usually small, resilient species, it is important that these stocks are monitored and some basic management applied.

References

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

WCPFC, 2017. Provisional outcomes document, WCPFC14-2017-outcomes, from the Western & Central Pacific Fisheries Commission Fourteenth Regular Session (As at 18 December 2017), 3-7 December 2017, Manila, Philippines. 15 pp. Available at https://www.wcpfc.int/meetings/wcpfc14 {Accessed on 18.12.2017]

WCPFC, 2017. Summary Report of 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. 281 pp. Available at https://www.wcpfc.int/meetings/sc13 [Accessed on 27.11.2017]