Tuna, skipjack

Euthynnus pelamis, Katsuwonus pelamis

Method of production — Caught at sea
Capture method — Pole & line
Capture area — Western Atlantic (FAO 21,31,41)
Stock area — West Atlantic
Stock detail

All Areas


Picture of Tuna, skipjack

Sustainability rating two info

Sustainability overview

Skipjack stocks are difficult to assess. The latest stock assessment for the West Atlantic was undertaken in 2014. Results suggest that it is unlikely that the stock is overfished (probably close to 1.3Bmsy) nor being subject to overfishing (probably close to 0.7Fmsy). Maximum Sustainable Yield (MSY) was estimated to be around 30 -32,000t and recent catches are below this. There is concern regarding the under reporting of skipjack catches in the Atlantic. There are no specific management measures for skipjack in the West Atlantic. Approximately 91% of the bigeye in the West Atlantic is caught in pole and line surface fisheries which are selective yet rely on large amounts of live bait fish. Whilst the scale of this is unlikely to overexploit stocks of these species, it 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 34 kg 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

West Atlantic

Stock information

Skipjack and other tuna stocks in the Atlantic are assessed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). In the West Atlantic the major fishery is the Brazilian bait boat fishery, followed by the Venezuelan purse seine fleet. West Atlantic annual catches have been relatively stable over the last 20 years, following the historic record of 40,272 t in 1985. Preliminary catches for 2016 were approximately 28,570 t, similar to the five year average of 29,427 t.

In all the oceans, the traditional stock assessment models are difficult to apply to skipjack because of their particular biological and fishery characteristics (on the one hand, continuous spawning, spatial variation in growth and on the other, discrimination of effort for free schools and FADs, transition between these two fishing methods which are difficult to quantify). In order to overcome these difficulties, several assessment methods have been applied to the two stocks of Atlantic skipjack. Based on the large geographic distances between the fishing areas and current knowledge on small-scale migrations of skipjack in the Atlantic, the Scientific Committee has also analysed the possibility of using smaller stock units than east and west Atlantic, but for now continues to stick with these two main units. It is expected that the five year Atlantic Tropical Tuna Tagging Programme (AOTTP), may improve understanding of skipjack stock structures and movement patterns. The latest stock assessment for the west Atlantic was undertaken in 2014. Results suggest that it is unlikely that the stock is overfished (probably close to 1.3Bmsy) nor being subject to overfishing (probably close to 0.7Fmsy). Maximum Sustainable Yield (MSY) was estimated to be around 30 -32,000t

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 address 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 International Commission for the Conservation of Atlantic Tunas (ICCAT). 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. There remain large data deficiencies in most tuna and billfish fisheries, particularly with regards to fine scale spatial and temporal data for both target and especially for vulnerable bycatch species. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.

The scientific committee recommends that the catch and effort levels do not exceed the maximum sustainable yield. In addition, increasing harvests and fishing effort for skipjack could lead to involuntary consequences for other species that are caught in combination with skipjack in certain fisheries (particularly juveniles of yellowfin and bigeye). There is concern regarding uncertainties which the underreporting of skipjack catches may have on the perception of the state of the stocks.

There are no specific management measures for skipjack in the West Atlantic, but ICCAT measures designed for yellowfin and bigeye are likely to impact skipjack. Other Atlantic wide measures include: A maximum of 500 purse seine FADs to be active at any one time and countries must have FAD Management Plans that improve understanding of FADs and limit their impacts on the ecosystem.
ICCAT maintains a list of vessels over 20m authorised to fish for these species, although other vessels may retain them as bycatch as long as the country sets limits on this and doesn’t exceed its quota.
Performance indicators and evaluations of the projected impact of current management measures are expected in 2017, with adjustments to management following in 2018.
Countries are encouraged to reduce discards.
There is a mandatory level of observer coverage of 5%, which may not have been implemented by many fleets, although some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips. This is in spite of scientific committee recommendation of a minimum of 20% for accurate reporting of bycatch. Purse seine and longline vessels over 20m long are encouraged to increase their observer coverage from the required minimum. Vessel Monitoring Systems are required for all vessels over 24m.<
ICCAT maintains lists of vessels authorised to fish for tuna and tuna-like species in the ICCAT area, and those caught carrying out Illegal, Unreported or Unregulated activities.
At-sea transhipment is prohibited unless pre-authorised and the vessel has an observer on board.
In 2017 ICCAT banned the discarding of skipjack, yellowfin and bigeye.
In 2016 the Commission passed measures to strengthen and streamline its compliance assessment process and to develop a scheme of responses to non-compliance.

Capture Information

Criterion score: 0.25 info

In the West Atlantic the major fishery is the Brazilian bait boat fishery, followed by the Venezuelan purse seine fleet. Pole and line fishing accounts for approximately 91% of skipjack catches in the Western Atlantic. Pole and line fishing is labour intensive, but is very selective and has the least impact on bycatch species. Substantial amounts of bait fish are used in these fisheries though and a better understanding of the impact to these stocks is needed. The average weight (3 to 4.5kg) of skipjack caught in the Western Atlantic is higher than in the East (2 to 2.5kg). This is primarily because the pole and line fleet targets larger fish than FAD associated purse seining.

ICCAT aims to take an ecosystem-based and precautionary approach to fisheries management.

For sharks: Countries are required to develop and submit National Plans of Action for the conservation and management of sharks. Sharks must be fully utilised (e.g. no removal of fins). Sharks must be released wherever possible (if not being directly targeted) and countries must try to minimise bycatch of sharks (although no gear-specific measures are identified). Catching silky sharks, hammerheads, oceanic whitetips, and bigeye threshers is prohibited, and catching other thresher species is discouraged. Shortfin mako can be caught and retained, but as of 2017 the country’s law must require a minimum length of 180cm for males and 210cm for females, otherwise, shortfin makos caught alive must be released unharmed. This is expected to prevent the stock’s currently poor state from worsening, and a rebuilding plan will be developed for 2019. In 2016 additional measures for blue shark were introduced, mainly focussed on improved data recording, with potential to introduce Harvest Control Rules. A catch limit of 39,102 t was also introduced in the north Atlantic (but none for the south Atlantic): if exceeded the commission has committed to reviewing the effectiveness of its blue shark management measures. Preliminary catch in 2016 was 42,117 t. Porbeagle is overfished throughout the Atlantic, significantly so in the northwest, and for the north Atlantic overall it is predicted to take at least 30 years to recover if there was zero fishing mortality. The main porbeagle-directed fisheries (EU, Uruguay and Canada) have closed, and ICCAT have a recommendation to release live porbeagle unharmed, but it is still caught incidentally and discarded, and also landed by other fleets. Currently there is not enough data to properly assess the status of many pelagic sharks (no assessments have been carried out for the Mediterranean).

There is a mandatory level of observer coverage of 5%, which may not have been implemented by many fleets, in spite of scientific committee recommendation of a minimum of 20% for accurate reporting of bycatch. However, some fleets are currently implementing voluntary observer programmes that cover 100% of fishing trips.

References

ICCAT, 2017. Report of the Standing Committee on Research and Statistics (SCRS) of the International Commission for the Conservation of Atlantic Tunas, 2-6 October 2017, Madrid, Spain. 465 pp. Available at http://www.iccat.int/com2017 [Accessed on 27.11.2017].

ICCAT, 2017. Resolutions, Recommendations and other Decisions. Available at http://www.iccat.es/en/RecsRegs.asp [Accessed on 12.12.2017]

Fishery Progress, 2017. Fishery Improvement Project Directory. Available at https://fisheryprogress.org/ [Accessed on 05.12.2017].

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

ISSF, 2017. Status of the world fisheries for tuna: November 2017. ISSF Technical Report 2017-02A. International Seafood Sustainability Foundation, Washington, D.C., USA. 98 pp. Available at: https://iss-foundation.org/about-tuna/status-of-the-stocks/ [Accessed on 20.11.2017].