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Skipjack tuna live in oceanic surface waters throughout the Indian Ocean and Western and Central Pacific Ocean, except in areas where ocean depth is less than about 50m. Skipjack also live in the Atlantic Ocean.
Skipjack is an important tuna species. Skipjack caught in the Asia-Pacific region contribute nearly half of total world tuna catch (all species) and about 80% of world skipjack catch. Over 70% of the total tuna catch of the Western and Central Pacific Ocean and about half that of the Indian Ocean is skipjack tuna.
Skipjack is caught by local fishers and foreign licensed vessels using many different fishing gears, from traditional to industrial, including purse-seine, pole-and-line, ring nets, gillnets, hand lines and troll lines.
SUSTAINABILITY AND MANAGEMENT
Skipjack is heavily fished but is an abundant, very resilient species that is fast-growing, short-lived, and very fecund. The skipjack resource is not overfished. The resource is managed by the Indian Ocean Tuna Commission (IOTC), the Western and Central Pacific Fisheries Commission (WCPFC) and national governments. International environment organizations and market controls have an influence on the governance of skipjack fisheries.
Skipjack is sold as canned tuna (90% of catch), with the better grade marketed as “light-meat tuna” mainly in Europe, the US and Australia/New Zealand. The remainder is sold fresh locally, dried-salted and smoked. Skipjack is canned in Thailand, Seychelles, Mauritius, Kenya, India (in the Indian Ocean) and Philippines, Papua New Guinea, Solomon Islands, Fiji, American Samoa, Ecuador (in the Pacific Ocean). Product from the Indian and Pacific oceans is also canned in Spain, Germany and Venezuela. Wherever it occurs, skipjack is also an important locally consumed fish.
The skipjack fishery provides tens of thousands of jobs in fishing and processing – including for women – although many fishing crew and processing workers are low-paid and their work arduous. Pacific and Indian Ocean country governments receive substantial revenue from granting foreign fishing licences.
As food, skipjack is a very good source of low-fat protein and is low in sodium, but has a moderate level of cholesterol.
ECOSYSTEM AND CLIMATE
Skipjack fishing bycatch, mainly juveniles of other tuna species but also of sea turtles, sharks and other marine fish species, is a significant environmental issue. Unless strictly managed, fish processing operations for skipjack (mainly by canning) also have negative effects on surrounding land and sea environments.
Global warming affects the distribution and catchability of skipjack stocks.
WILD HARVEST FISHERIES
All skipjack production is from wild harvest fisheries. Skipjack is heavily fished yet is abundant and very resilient because it is fast-growing, short-lived, and very fecund.
IUCN Red List Status
Least Concern http://www.iucnredlist.org/details/170310/0
State of the Stock(s) and Impacts of Fishing
The skipjack resources of the Western and Central Pacific Ocean (WCPO) and Indian Ocean (IO) are not overfished, nor is overfishing occurring. Certain fishing methods provide cause for environmental concern. The International Seafood Sustainability Foundation’s (ISSF Status of the Stocks Technical Report) assessment of the resource for each ocean states:
WCPO SKIPJACK TUNA
- Green – biomass is at or above stock biomass at maximum sustainable yield (BMSY)
- Green – fishing mortality less than fishing mortality at maximum sustainable yield (FMSY)
- Green – 44% of the catch is made with purse seining on free schools, with little impact on non-target species.
- Yellow – 36% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks); and 8% of the catch is made by pole-and-line fishing, with unknown impacts on baitfish stocks.
- Orange – 12% of the catch is made by other gears such as gillnets, with unknown impacts on non-target stocks.
IO SKIPJACK TUNA
- Green – biomass is at or above stock biomass at maximum sustainable yield (BMSY)
- Green – fishing mortality less than fishing mortality at maximum sustainable yield (FMSY)
Green – 3% of the catch is made with purse seining on free schools, with little impact on non-target species.
- Yellow – 40% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks); and 20% of the catch is made by pole-and-line fishing, with small bycatch of non-target species but unknown impacts on baitfish stocks.
- Orange – 24% of the catch is made by gillnets, a gear expected to have high bycatch rates. No mitigation measures are in place and monitoring is extremely deficient.
Certificates for sustainability of wild harvest fishery
Marine Stewardship Council (www.msc.org):
- PT Citraraja Ampat, Sorong pole and line Skipjack and Yellowfin Tuna certified November 2018 to November 2023.
- Parties to the Nauru Agreement (PNA – www.pnatuna.com) Western and Central Pacific Skipjack Tuna; for purse seine setting on unassociated/non-FAD free schools in the EEZs of Papua New Guinea, Kiribati, Federated States of Micronesia, Marshall Islands, Nauru, Palau, Solomon Islands and Tuvalu; certified December 2011 to March 2023.
- Maldives Pole & Line Skipjack Tuna: for pole and line fishing, Western Indian Ocean; certified November 2012 for 10 years.
- Tri Marine Western and Central Pacific Skipjack and Yellowfin Tuna: certified June 2016 for 5 years.
- Solomon Islands skipjack and yellowfin tuna purse seine and pole and line: certified July 2016 for 5 years.
- Japanese Pole and Line skipjack and albacore fishery: certified October 2016 for 5 years.
- Echebastar Indian Ocean purse seine skipjack tuna: Eastern and Western Indian Ocean; certified November 2018 to November 2023.
- Western Pacific Sustainable Tuna Alliance (WPSTA) Western and Central Pacific skipjack and yellowfin free school purse seine; certified June 2018 to June 2023.
Several other skipjack fisheries are under assessment.
Friend of the Sea (www.friendofthesea.org)
- Does not certify fisheries, but rather tuna purse seine and longline fleets, including some company fleets fishing for skipjack in the Asia-Pacific region.
Several conservation and sustainable/fair food organizations also promote sustainable tuna campaigns, e.g., see the Pew Charitable Trusts Global Tuna Conservation campaign.
Skipjack is a difficult species to assess, due to its high and variable productivity and its continuous and variable recruitment that make growth estimates difficult.
Western and Central Pacific Ocean
For the WCPO skipjack stock, status assessment and data management services are provided by the Oceanic Fisheries Programme of the Secretariat of the Pacific Community (SPC) and reviewed by the Scientific Committee of the Western and Central Pacific Fisheries Council. Skipjack assessment is based on catch, effort, fish size and tagging data. Japanese pole-and-line catch-per-unit-effort (CPUE) time series is used to estimate biomass trends, assumptions are made about growth (Hoyle et al, 2011) and adjustments made for estimated misreporting of species composition of skipjack, yellowfin-bigeye (Hampton & Williams, 2011). The International Sustainable Seafood Foundation takes the Western and Central Pacific Fisheries Commission stock assessments, plus other reliable information, in making their sustainability assessments of stock abundance, fishing mortality and environment.
Fishing mortality on skipjack has increased since 1972, particularly in the western region. While estimates of fishing mortality for skipjack have increased over time, current fishing mortality rates for skipjack tuna are estimated to be about 0.45 times the level of fishing mortality associated with maximum sustainable yield (FMSY). Therefore, overfishing is not occurring (i.e. Frecent < FMSY) (McKechnie et al., 2016). Even so, skipjack is being exploited at a moderate level relative to its biological potential.
At its most recent Scientific Committee meeting, WCPFC notes that under recent fishery conditions (2017 catch level for longline and other fisheries and effort level for purse seine), the skipjack stock was initially projected to decrease for a short period. In the longer term, assuming long term average recruitment, modest increases in the stock were projected (WCPFC, 2018).
The aggregate Indian Ocean skipjack population is determined to be not overfished and is not subject to overfishing (IOTC, 2018). The final overall estimate of stock status indicates that the stock is at the target biomass reference point and that the current and historical fishing mortality rates are estimated to be below the target. Over the history of the fishery, biomass has been well above and the fishing mortality has been well below the established limit reference points. Current spawning stock biomass relative to unexploited levels is estimated at 40%.
The skipjack resource is managed by regional tuna fisheries management organizations (RFMOs) and by national governments.
Industrial tuna fisheries are managed by the Indian Ocean Tuna Commission (IOTC) and the Western and Central Pacific Fisheries Commission (WCPFC). The Inter-American Tropical Tuna Commission (IATTC) management area encompasses the Eastern Pacific, with some overlap with the WCPFC Convention Area. The RFMOs meet annually to consider and endorse recommended management actions. [See Slide Show for convention area maps]
Regional associations, such as the Parties to the Nauru Agreement (PNA) are increasingly influential in tuna fisheries management. Individual island countries also manage their tuna resources, through national tuna management plans.
Each of the tuna RFMOs has a scientific committee that advises the RFMO management on stock status, monitoring and management advice and implications using their own and additional scientific advice provided by specialist organizations and individual national experts. The scientific committees also maintain databases for the catch, effort, size frequency, tagging, biological data, observer, sampling and other data.
On the 'receiver' end, the EU regulations against illegal, unreported and unregulated (IUU) fishing vessels (Council Regulation (EC) No. 1005/2008 and Commission Regulation (EU) No 468/2010) and the bans imposed by some marketing chains (in UK, USA) on canned tuna harvested around fixed FADs are, in effect, management measures. International environment campaigns by organizations such as Greenpeace, the Pew Environment Group and WWF increasingly target skipjack management decisions, especially on FAD fishing and bycatch.
Western and Central Pacific Ocean
Western and Central Pacific Convention Area management measures include port inspections, at-sea inspections, an observer program, regional programs, positive vessel list (vessels authorised to fish in flag States of RFMO member countries), IUU vessel lists, release tool for sea turtles (Miyake et al, 2010), fishery closures, total allowable catch and effort, ‘freezing’ vessel capacity, reducing excess fleet capacity, reducing 'trading' of fishing effort, and obligatory carrying of satellite-linked tracking devices. The first management action limiting fishing in the WCPFC Convention Area was adopted in December 2008. It incorporated an annual three-month closure for purse-seine fishing on FADs, other floating objects and whale sharks. It required that all caught tuna be retained on board (WCPFC, 2008: CMM2008-01).
Regional inter-governmental and industry organizations concerned with tuna in the Western and Central Pacific are:
- Pacific Islands Forum Fisheries Agency (FFA) - (member countries: Australia, Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, New Zealand, Niue, Palau, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu and Vanuatu)
- Parties to the Nauru Agreement (PNA) - (member countries: Federated States of Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu).The influence of the PNA in tuna management in the WCPFCA has been significant because, as a group, the member countries host the largest skipjack resources.
- TVMA (Te Vaka Moana Arrangement) - (member countries: Cook Islands, New Zealand, Niue, Samoa, Tokelau and Tonga)
- Pacific Islands Tuna Industry Association (PITIA) - (member countries: Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Palau, Papua New Guinea, Solomon Islands, Tonga, Tuvalu, Vanuatu)
IOTC management measures include port inspections, an observer program, transshipment controls, use of VMS (for vessels greater than 15 m and fishing on the high seas: ISSF, 2011c), limitations on fishing capacity (Resolution 12/07), gear (Resolution 12/12) and area closures (Resolution 12/13), electronic logbooks for purse-seiners, a vessel registry, positive vessel list, IUU vessel list, required use of a release tool for sea turtles, and other conservation measures (for sea birds and sharks) not relevant to the skipjack fisheries. The Indian Ocean Tuna Commission (IOTC) is developing criteria for a quota allocation system.
Skipjack are not produced in aquaculture.
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below.
For IUCN Red List, see Bruce Collette and colleagues (2014) and https://www.iucnredlist.org/species/170310/6739812
For stock status information, see the IOTC Report (IOTC, 2018), and WCPFC SC Summary Report (WCPFC, 2018b).
For environmental issues, see IOTC Report (IOTC, 2018) and SC Summary Report (WCPFC, 2018), and Tyedmers & Parker (2012) on fuel consumption.
For fisheries management information, see IOTC and WCPFC Working Papers, CMMs, Resolutions and Summary Reports. WCPFC CMM link: http://www.wcpfc.int/conservation-and-management-measures, IATTC Resolutions link: http://www.iattc.org/ResolutionsActiveENG.htm, and WCPFC (2018).
- Collette, B, A Acero, AF Amorim, A Boustany, C Canales Ramirez, G Cardenas, KE Carpenter, N de Oliveira Leite Jr, A Di Natale, W Fox, FL Fredou, J Graves, A Guzman-Mora, FH Viera Hazin, M Juan Jorda, O Kada, C Minte Vera, N Miyabe, R Montano Cruz, R Nelson, H Oxenford, E Salas, K Schaefer, R Serra, C Sun, RP Teixeira Lessa, PE Pires Ferreira Travassos, Y Uozumi, & E Yanez. 2011. Katsuwonus pelamis. The IUCN Red List of Threatened Species 2011: http://www.iucnredlist.org/details/170310/0
- Hampton, J and P Williams. 2011. Misreporting of purse seine catches of skipjack and yellowfinbigeye on logsheets. WCPFC-SC7-2011/ST-WP-02, Pohnpei, Federated States of Micronesia, 9–17 August 2011.
- Hoyle, S, P Kleiber, N Davies, S Harley and J Hampton. 2011. Stock assessment of skipjack tuna in the western and central Pacific Ocean. WCPFC-SC7-2011/SA-WP-04, Pohnpei, Federated States of Micronesia, 9–17 August 2011.
- IOTC (Indian Ocean Tuna Commission). 2018. Report of the 21st Session of the IOTC Scientific Committee. Seychelles, 3 – 7 December 2018.
- McKechnie, S, J Hampton, GM Pilling and N Davies. 2016. Stock assessment of skipack tuna in the western and central Pacific Ocean. WCPFC-SC12-2016/SA-WP-04, Bali, Indonesia, 3 – 11 August 2016.
- Tyedmers, P & R Parker. 2012. Fuel Consumption and Greenhouse Gas Emissions from Global Tuna Fisheries: A preliminary assessment. ISSF Technical Report 2012-03. International Seafood Sustainability Foundation, McLean, Virginia, USA.
- WCPFC (Western and Central Pacific Fisheries Commission). 2016. Twelfth Regular Session of the Scientific Committee Summary Report Retrieved from Bali, Indonesia: https://www.wcpfc.int/meetings/sc12
- WCPFC (Western and Central Pacific Fisheries Commission). 2018a. Summary Report. Fourteenth Regular Session of the Commission, 3 – 7 December, 2017, Manila, Philippines. 389p. https://www.wcpfc.int/system/files/WCPFC14%20Summary%20Report%202017_%20Issued%2016%20March%202018_complete.pdf
- WCPFC (Western and Central Pacific Fisheries Commission). 2018b. Summary Report. Fourteenth Regular Session of the Scientific Committee, 8 – 16 August, 2018, Busan, South Korea. 307p. https://www.wcpfc.int/file/225081/download?token=1E3BSSlB
Globally, skipjack is among the top 10 aquatic species, by quantity, produced. Skipjack caught in the Western and Central Pacific and the Indian oceans comprises nearly half of total world tuna production (all species) and about 80% of world skipjack catch. Skipjack comprise about 70% of the total tuna catch of the Western and Central Pacific Ocean (FFA, 2011) and about 49% of the total tuna catch of the Indian Ocean (IOTC, 2011c).
Currently, about 2 million t of skipjack are harvested from the Asia-Pacific: about 1.5 million tonnes (t) from the Western and Central Pacific Ocean (WCPFC, 2012a) and 0.5 million t from the Indian Ocean. This quantity comprises almost one half of total global tuna catches.
Skipjack is caught by local fishers and/or foreign licensed vessels using many different fishing gears, from traditional to industrial and recreational, including purse-seine, pole-and-line, ring nets, hand lines, troll and gillnets. (Lehodey et al, 2011; Hoyle et al, 2011). Most skipjack fishing targets surface schools that occur naturally, e.g., around floating objects, or that are aggregated by human actions, e.g., by drifting and fixed fish aggregating devices (FAD) and chumming with bait.
Developing countries' fleets are very diverse (Miyake et al, 2010) and range from coastal and artisanal, through semi-industrial to fully industrial vessels; developed country fleets are industrial scale and much less diverse.
SMALL SCALE FISHERIES AND LARGE AND INDUSTRIAL SCALE FISHERIES
Purse seining is the major fishing method for skipjack. Purse seine fleets usually operate in equatorial waters from 10°N to 10°S. The sizes of national fishing fleets has fluctuated widely in the last 10 years, in response to markets, costs (e.g. fuel), size of the resource, and access to fishing areas. Over the past four to five years, the U.S. and China purse seine fleets have expanded, the additions to the fleets being large boats with increased fish hold capacity. Purse-seining is a highly technological fishing operation and is capital intensive; new industrial scale vessels costing at least US$25 million (Barclay & Cartwright, 2007); smaller nationally registered vessels costing less.
Floating fish aggregation devices (FADs) aid the harvest of tunas in the purse seine fishery and have led to the expansion of fishing grounds and seasons. The type of association of tunas and floating or anchored devices has become a prime issue in tuna management, most notably for yellowfin and bigeye tuna.
Purse seine vessels primarily target surface-swimming skipjack, and also catch small yellowfin and bigeye tuna. Catches associated with floating objects (e.g., natural logs and FADs) are largely of skipjack; the yellowfin component being much less than that of skipjack and bigeye catches (in weight) (Miyake et al, 2010). In free (unassociated) sets, yellowfin dominate the catch in the Indian Ocean (IOTC, 2011a; Pianet et al, 2011), but skipjack dominate in Western and Central Pacific Ocean sets.
Western and Central Pacific Ocean
Many Western and Central Pacific Ocean domestic fleets operate around anchored FADs (Babaran, 2006). Small-scale artisanal fisheries, including in the Philippines and Indonesia, include boats that use trolling gear, and various fishing gear such as hand lines/hook and line, ring nets, pole-and-line, trolling, and traditional methods (Lehodey et al, 2011, Hoyle et al, 2011). Trolling is a particularly common fishing method in nearshore waters of the Pacific, and enhanced where anchored FADs are available.
Operating on the high seas and, under agreements, in EEZs, fishing fleets from Korea, Taiwan Province of China, Japan, and the USA account for just over 50% of the Western and Central Pacific Ocean purse seine catch. Most of the remaining purse seine catch is taken by vessels based in Pacific Islands countries fishing under the Federated States of Micronesia (FSM) Arrangement that permits domestic vessels of PNA members to access the fisheries of other PNA members on terms similar to those of the distant water fleets, and Philippines vessels. Catches by fleets flagged to or chartered by Pacific Island countries (part of their domestic fleets) have much increased in recent years (Oceanic Fisheries Programme, 2012, Lehodey et al, 2011).
In addition to purse seine vessels, the skipjack fisheries include the Japan distant-water (temperate north Pacific) and offshore pole-and-line fleets, and Japan domestic pole-and-line fleets based in island countries (Hoyle et al, 2011). Artisanal and ‘other’ gears contribute only minor amounts to the total catch (Williams & Terawasi, 2011).
The majority of the Indian Ocean skipjack catch is taken in the Western Indian Ocean (Pianet et al, 2011) and, increasingly, south of India and Sri Lanka (IOTC 2011a). About half the total skipjack catch is by ‘non-industrial’ fishing gears (IOTC, 2011c), many of which are mechanized, large-scale driftnet (Iran and Pakistan) and multi-day gillnet vessels (Sri Lanka) classified as ‘semi-industrial’ (MRAG, 2012; IOTC 2012b).
In the Indian Ocean, four main fishery types target skipjack (Kolody et al, 2011): pole & line (specifically, the Maldivian Pole-and-Line fleet but also Minicoy in India); log-associated purse seine sets from the European Union (EU)/Seychelles fleets; unassociated (or free) purse seine sets from the EU/Seychelles fleets; and ‘other’ – that includes purse seine from other nations and all other fleets (primarily gillnet fleets from Sri Lanka, Iran, Oman (Adam, 2010), Pakistan and Indonesia).
Most of the recent catch increases are from the gillnet fisheries of Sri Lanka, Indonesia, Iran and Pakistan. Historically, these fleets mostly operated in coastal waters but in recent years long distance trips to international waters have become more common (Kolody et al., 2011). Vessels from Iran and Sri Lanka have been using drifting gillnets even on the high seas in recent years, reaching as far as the Mozambique Channel. The activities of these fleets are poorly understood and limited fishing data are provided (IOTC, 2011c).
Small-scale artisanal fisheries in the Indian Ocean include boats that use trolling gear, and various other fishing equipment such as hand lines/hook and line, ring nets, pole-and-line, trolling, and traditional methods (Lehodey et al, 2011, Hoyle et al, 2011), especially in coastal or gulf parts of the Indian Ocean.
Skipjack is an important game fish usually taken by trolling on light tackle using plugs, spoons, feathers, or strip bait (Collette, 2001).
Skipjack are not produced in aquaculture.
Skipjack is canned, sold fresh, dried-salted and smoked. In addition to the harvesting operations, the tuna supply chain supports many post harvest jobs and companies. Indirectly, tuna fishing benefits to the economy, including employment and fees from foreign fishing vessels, are significant and can be up to four times the value of the actual fish harvest (Ahmed et al, 2010).
Once caught, the skipjack may be transshipped to tender boats – refrigerated fish carriers or reefers that, basically, are trucks-at-sea to carry the catch to the canneries ashore. This facility enables the seiners to keep on fishing, and also creates efficiencies by separating the fishing roles of capture and transport. Transshipments must be monitored by observers, and as a rule, RFMOs prohibit transshipping at sea – although exceptions are permitted in archipelagic and territorial waters of some member countries of the WCPFC. Transshipping regulations are one of the measures for stamping out illegal, unreported and unregulated (IUU) fishing activity.
At the cannery, tuna are pressure-cooked, then sorted, gutted, finned, skinned, and de-boned. The flesh is then either placed into vacuum-sealed packages (‘pouche’) and dispatched to (usually) western processors for further processing, or packed into cans into which vegetable oil (or brine) and sometimes flavourings are added, before the cans are sealed and re-cooked, then labeled for sale.
Skipjack from the Western and Central Pacific and Indian oceans is canned in factories in Thailand, Seychelles, Mauritius, Kenya, India (in the Indian Ocean) and Philippines, Papua New Guinea, Solomon Islands, Fiji, American Samoa, Ecuador (in the Pacific Ocean). Product from these oceans is also canned in Spain, Germany and Venezuela. Higher grade skipjack is sold as ‘light-meat tuna’ mainly in Europe, the US and Australia/New Zealand (Miyake et al, 2010, Hamilton et al, 2011).
Thailand is the world leader in canned tuna production, including skipjack. Most of the Thai canned skipjack is purchased from catches outside Thai waters, including especially from catches in other Asia-Pacific countries. Philippines and the USA are second and third in terms of amount of skipjack canned (Hamilton et al., 2011).
Papua New Guinea is an important supplier of skipjack pouches to the Spanish and German canneries. The number of canneries in Papua New Guinea has increased since the RD Tuna cannery was established in 1977: six canneries now are built or planned (Lae, Madang, Wewak), to eventually employ more than 15,000 people (PNG National Fisheries Authority, pers comm.).
For small island economies such as American Samoa, the Seychelles, Mauritius, the Solomon Islands and the Marshall Islands, expansion of canning is constrained by weak infrastructure (poor harbour and land development, lack of investment capital) and high import costs for inputs such as canning materials. One example is Papua New Guinea’s canned tuna industry which has to compete in a sector with low-margins, high product volumes and strong retail market pressure to reduce prices (Hamilton et al, 2011).
SALTED AND DRIED PRODUCTS
Japan and other Asia-Pacific countries, produce commercial and artisanal dried and salted skipjack products – such as katsuobushi (Japan), hikimas (Maldives, Lacshadeep islands, India), Maldive Fish (Maldives), balaya (Sri Lanka). Katsuobushi is made of flakes or shavings of dried and smoked skipjack (bonito) tuna, and used widely in Japanese cooking as a condiment and as a key ingredient in soup broths (dashi) and sauces.
SASHIMI AND OTHER PRODUCTS
Skipjack is also sold fresh or frozen. Some pole-and-line fleets have established a sashimi market for high-quality frozen skipjack in recent years, particularly targeting consumers in the Pacific countries (Miyake et al, 2010).
Common Market Names
Skipjack is known by many local common names (e.g., see FishBase – http://www.fishbase.org – for lists) but, due to its large global market, is usually known at also country level as "skipjack" or "skipjack tuna".
Skipjack is low in fat, especially saturated fat and in sodium. Skipjack tuna is a very good source of protein and selenium. It has medium levels of cholesterol (compared to shellfish, red meat and animal products such as eggs) but no information is available on the breakdown of cholesterol into HDL (“good”) and LDL (“bad”) types.
Per 100 g of raw product, skipjack contains approximately:
|Kilojoules||418 (100 calories)|
|Total fat (oil)||0.4g|
|Omega 3 EPA||13mg|
|Omega 3 DHA||96mg|
|Omega 6 AA||15mg|
Sources: Mooney, et al. (2002) for fat (oil) content of Australian fish, other figures from NOAA FishWatch for eastern Pacific skipjack.
Trade and Markets
In the Asia-Pacific region, skipjack is a major food commodity of political and economic importance due to the large volume harvested, its high share of global skipjack production, its value and international fishing and market access arrangements that have impacts on and beyond fisheries. Prices of frozen skipjack for canning are comparable throughout the world because the raw material varies little with season, area and size, most of it is canned, and it has few competitors (Miyake et al., 2010).
About 90% of the Asia-Pacific skipjack catch is canned. The main costs in the skipjack canned fish supply chain: are purchase of tuna, capital investments, labour costs, freight costs, licence fees and fuel costs (Barclay & Cartwright, 2007). In the final price of canned tuna, the purchase of fish costs 39-48%, price of can 17-20%, labour costs 6-8%, sea freight 5-6%, by-product sales -2%, utilities 6-8%, fixed overheads 5-6%, brine/oil filling 1-5%, cardboard sleeves and outer cases 3% and marketing 3-4% (Campling & Doherty, 2007).
Skipjack and other tunas are the subjects of several international market access and trade preference agreements.
The world’s largest canned tuna market is the USA but its consumer demand has declined due to changing product lines, consumer preferences and lower quality raw material from yellowfin and skipjack caught on associated-FAD fishing. Many of the big USA brands of canned tuna require ‘dolphin-safe’ tuna (Hamilton et al, 2011) as a result of USA actions and legislation that began in the Eastern Pacific Ocean in the 1980s.
For the EU market, eligible Pacific Island States use the EU Lomé/Cotonou Agreement trade preference designed to help the countries attract foreign direct investment, create employment and stimulate the economies (Campling et al, 2007). It enables access to EU markets for tuna products. Pacific island and Indian Ocean countries also have other forms of preferential market access available under the EU’s Generalised System of Preferences (GSP) and the EU-Economic Partnership Agreement (EPA) that enables eligible countries meet EU “rules of origin” requirements (Hamilton et al, 2011, Havice & Reed, 2012).
The UK canned tuna market, especially the large retailers, has been targeted by some environmental groups that advocate sales of products that come only from sustainable sources, defined by these groups to be from pole-and-line and FAD-free fisheries. Several major retailers have changed or intend to change the sourcing policies for own-brand canned tuna (Pala, 2011).
In addition to large markets for skipjack in Europe and the United States, canned skipjack is eaten also across the Western and Central Pacific. In the Western and Central Pacific, fresh skipjack is very popular in Polynesia (e.g. in French Polynesia from the specialist ‘bonitier’ fishery); and is well-liked in much of Micronesia. In Melanesia, most consumption of skipjack is limited to the urban centres or communities close to canneries where smaller-sized skipjack are unloaded from industrial vessels and sold or traded for local consumption.
Employment, Social Factors and Gender
The skipjack tuna fishery is a very significant employer in fishing and processing operations. It provides tens of thousands of jobs in the Asia-Pacific region – including for women. In 2008 in the Western and Central Pacific, nearly 10 times as many local jobs were in shore-based processing (about 11,000) compared to local jobs on tuna vessels (Bell et al., 2009, Bell et al, 2011). Total employment on all vessels, enterprises and from all countries, however, is not available.
To keep labour costs low, many canneries have been developed near areas of labour supply in low-cost Pacific and Indian Ocean Island States (Campling & Doherty, 2007). These are also close to the tuna stocks through fishing access agreements to EEZs and port facilities for transshipment. In the case of Thailand, labour costs are reduced by bringing in low cost immigrant labour from, for example, Myanmar and Bangladesh.
The skipjack fishery benefits people all over the world but is particularly important to people in the Pacific region, parts of Asia and to coastal communities in the Indian Ocean because it provides high-protein food, income and employment. More significantly, tuna will need to provide much of the additional fish for food security as the populations of the Pacific grow (Bell et al., 2011).
Because of the scale and importance of the skipjack and other tuna fisheries, focus has been almost solely on the direct benefits. Recently, however, attention has also turned to the conditions for workers on vessels and in canneries and the impacts on the environment. Skipjack products supply a highly competitive global market, creating strong incentives to keep supply chain costs low. At the present state of knowledge, the existence of serious problems in the treatment of crew on vessels and of workers in canneries is apparent from documented cases, but the prevalence of these problems is unknown.
In tuna science and management in selected Pacific island countries (Solomon Islands, Marshall Islands and Tonga), (Tuara and Passfield, 2011) found more men were employed than women. Women made up 18% of staff in government fisheries agencies, environmental institutions and environmental non-governmental organisations (NGOs). When fishing vessel observers were removed from the statistics, women’s participation increased to 25%. However, women comprised more than 60% of those in administrative and clerical jobs in government agencies.
Market pressures create conditions in which some fishing vessels are operated unsafely, fishing operations circumvent regulations and do not comply with relevant UN and ILO standards. At the worst, cases have been documented in the Asia-Pacific of illegal fishing vessels operated outside laws and social norms, using forced labour and abandoning crew in foreign ports. Some crew sexually abused children during port visits and fellow crew at sea, and used prostitutes in port (de Coning, 2011).
Almost all at-sea workers on vessels catching skipjack are males, and some boys (under 18 years). In Fiji in 2001, only 3% of people in the harvesting sector were women (Tuara Demmke, 2006). Many crew members on vessels from higher income countries, e.g., Japan, USA, Taiwan and Thailand, are workers from low-wage countries.
In the environmental campaigns that promote tuna pole-and-line fishing and oppose purse seine and associated-FAD fishing, several social as well as environment benefits of pole-and-line have been mentioned, such as that it offers enhanced employment opportunities for local crews because eight to nine times more labour is needed to catch a ton of tuna, and that it is fun and exciting for the fishers (Gillett, 2011). However, the promotion of social and environment benefits has not resulted in large new investments or revitalization except in the Maldives (Gillett, 2011), likely due to its complexity and unprofitability. Fishing for bait fish for the pole and line fishery may also interact with other local fisheries for human food.
Canneries and loining factories have become the most major employers in tuna supply chains. Most are now located in developing countries where labour costs are lower, although lower labour productivity partly offsets this (Hamilton et al., 2011). Women form a major share of the cannery workforces, especially in the Pacific, although they are rarely in supervisor and management positions. Up to date statistics on the numbers of employees and the breakdown by gender, however, are not available. In Thailand tuna processing plants migrant workers are engaged, including underage women and men (de Coning, 2011).
Among the unskilled workers who form the majority, men undertake the loading and other more physically-demanding tasks, and women work primarily on the processing lines. Canneries prefer to engage women processors because they are considered more deft than are men at cleaning and cutting the fish, and they accept (i.e. are paid) lower wages than men. All work long hours, have little job security (Sullivan, 2011). Workplace hazards and high risk work cause many health issues (Jeebhay et al., 2004). In some countries, workers cannot join or form trade unions and have little legal protection.
Industrial tuna processing affects different groups of people in distinct ways. Whereas the economic opportunities of the industry are recognised, employees’ expectations of good jobs and wages, education, roads, medical services and certain material goods often are not realised. Furthermore, communities’ well-being and societies may be negatively affected by losing the informal household and community support efforts of the cannery workers (Tuara Demmke, 2006; Parriss, 2010; Havice & Reed, 2012).
However, new industry accreditation schemes for social accountability may lead to addressing issues such as fair working hours and conditions, and workers income, job security, and freedom to form associations.
All fishing gears have some level of environmental effect. For skipjack, bycatch is one of the most noticeable effects (ISSF, 2012), but air and water pollution are other environment concerns. Ocean climate and global warming affect the distribution and catchability of skipjack stocks.
Effects of Fishing on Other Species
In the equatorial regions of the Indian and Western and Central Pacific oceans, the surface fishery for skipjack (purse seine and pole-and-line) also catches the smaller size classes (< 80 cm) of juvenile yellowfin tuna and juvenile bigeye tuna, and, in fishing free schools in the Western and Central Pacific Ocean (Harley et al., 2013), larger (>100cm) yellowfin tuna. Development of FAD fishing in the 1990s (and the later development of anchored or fixed FADs) led to higher fishing efficiencies and catch rates but also higher catches of juveniles and discards (Miyake et al, 2010, Leroy et al., 2012). Of the order of 40,000 FADs, and increasing, may be deployed in the WCP and IO for tuna fishing (Baske et al. 2012). A set on a FAD school catches many fish other than tuna. Juvenile bigeye are caught by FAD fishing and, because the stock size of bigeye is far smaller than the stock size of the other tunas caught under FADS (yellowfin and skipjack), the effect of the purse seine catch on the bigeye stock is greater than it is on the latter. The two main effects of FAD catches on juvenile bigeye are a reduction in bigeye stock size (also an effect of any other fishery including longline), and the potential reduction in yield (“growth overfishing”) of bigeye in longline fisheries (which target spawning-size bigeye). The effect on yellowfin stock is similar but not as significant.
Most RFMOs have mitigation measures in place for sea birds and sea turtles. In the Indian Ocean, cormorants, migratory shearwaters (which are common in coastal waters of many IOTC coastal states), sea turtles and sharks, are particularly vulnerable to bycatch in gillnet fisheries (IOTC, 2011c, MRAG, 2012). Sea turtles caught in fishing operations are usually discarded, and about 50% of the turtles are alive when brought in (MRAG, 2012). In the Western and Central Pacific, attempts have also been made to prohibit fishing activities for schools of tuna associated with whale sharks because of the FFA members’ concern about accidental mortality of the sharks (FFA Members, 2010; Pew Environment Group, 2012); the PNA introduced a ban in 2010, supported and extended by the Western and Central Fisheries Commission (WCPFC) in December 2012 (WCPFC, 2012b).
In the case of the pole-and-line fishery for skipjack in the Western and Central Pacific Ocean, the effect on baitfish resources (which are coastal) has a limiting effect on pole-and-line fishing in eastern parts of the Western and Central Pacific Ocean and would be a limiting factor in reviving the pole-and-line fishery which has been in a long decline, despite proposals to integrate community-based baitfishing (Gillett, 2011).
Impacts on Air and Water
Exhaust fumes and refrigerant gases from fishing vessels and processing plants contribute to global warming. The estimated total carbon footprint of purse seine-caught tuna in 2009 was approximately 1,530 kg CO2 per tonne of tuna landed, 75% of which is directly or indirectly (e.g. extraction, processing, and transport) from the consumption of fuel by the fishing vessel (Tyedmers & Parker, 2011).
Modern tuna fishing relies heavily on fossil fuel. Fuel consumption by vessels typically exceeds the energy use and greenhouse gas (GHG) emissions from processing, packaging and transport of resulting products combined (exceptions include when fresh products are transported by air). Compared to purse seine fisheries, pole-and-line fisheries targeting skipjack, and troll fishing, have much higher fuel use intensity (Tyedmers & Parker, 2011).Purse seine vessels fishing for skipjack are more fuel-efficient than purse seiners targeting other tuna species (ibid).
Tuna processing can have significant environmental effects if not properly conducted and regulated. For skipjack, most initial processing is done in low-cost countries where waste discharge has grown considerably (Havice & Reed, 2012) and where the regulation and monitoring of waste discharge is often weak. Other issues, especially for island states, are the high use of water in all stages of processing, energy use, noise, odour and solid waste (UNEP, 2000).
Effects of Environment on Skipjack
As an oceanic species, ocean climate conditions have pronounced effects on skipjack and its fisheries, especially the El Niño Southern Oscillation (ENSO) in the Western and Central Pacific Ocean. ENSO is a swing between a warmer (El Niño) and cooler (La Niña) ocean conditions across much of the tropical Pacific and that occurs on irregular cycles (2-7 years) due to interactions between the atmosphere and the ocean (Lehodey et al, 2011). ENSO affects skipjack through its affects on ocean currents and temperatures (Ganachaud et al. 2011) that influence where and when fish spawn, and how larvae, juveniles and their prey are dispersed or retained in areas conducive to their growth and survival (Lehodey et al, 2011). In the Western and Central Pacific Ocean, skipjack recruitment is linked to ENSO events; the biomass of fish recruited to the stock is positively correlated with the Southern Oscillation Index value of eight months earlier (Lehodey et al, 2011). In El Niño conditions, skipjack biomass is higher than in La Nina conditions (Lehodey et al. 1997).
ENSO also affects where the larger skipjack catches are taken in the Western and Central Equatorial Pacific. During El Niño (warm) events, higher purse-seine catches are taken in the central Pacific, e.g., Kiribati (Line Islands). Several months after an El Niño is completed, catches increase in the Solomon Islands and PNG, and particularly when an El Niño is followed by a La Niña (Lehodey et al, 2011).
Effects of Climate Change on Skipjack
In the shorter term (by 2035), fisheries for skipjack across the western and central-eastern Pacific are projected to gain from a warming ocean (Lehodey et al. 2011, Bell et al. 2011). However, by mid century, catches of skipjack in the western Pacific are expected to begin to decline, whereas those in the central-eastern Pacific are projected to remain significantly higher than the average catches made between 1980 and 2000 (Lehodey et al. 2011). One reason for these projections is that skipjack tuna are expected to move to areas within their preferred temperature range as sea surface temperatures (SST) increases. However, once SST in areas of the ocean exceeds the thermal maxima for skipjack, negative effects on skipjack populations will occur. By 2100, the effects of climate change are expected to cause a 5-10% decline in skipjack production relative to 1980-2000 catch levels (Lehodey et al. 2011).
The main fishing grounds and the catchability of skipjack in the surface fishery in the tropical Pacific are expected to change in a manner akin to the changes observed during present-day El Niño events. Prime skipjack fishing grounds are expected to move eastward along the equator, and towards higher latitudes, changing the location of suitable fishing areas for Pacific Island countries (Lehodey et al; 2011). Where skipjack remains within its preferred temperature range, catch rates of surface schools may increase as the water column becomes more stratified due to increasing SST and decreasing salinity.
All life cycle stages of skipjack are also expected to be affected by the projected changes to the nutrients in ocean surface layers, which affect the natural food available for fish (Le Borgne et al. 2011). Complex climate-related changes could result in trophic cascades, i.e., linked increases or decreases in the availability of prey or predators when the abundance of one or the other changes within the oceanic food web (Griffiths et al, 2010).
The skipjack is a small to medium size fish with an elongate, round-and-tapered body. The back is dark purplish blue, the lower sides and belly silvery. There are four to six very conspicuous dark bands along the body (appear as dark blotches in live fish). The body lacks scales except for the area behind the pectoral fins and along the lateral line. Skipjack has two dorsal fins separated by a short interspace; the dorsal and anal fins are followed by 7-9 finlets. There is a strong keel on each side of the caudal fin base between two smaller keels. The gill rakers are numerous, 53-63 on the first gill arch (Fishbase; Collette, 2001).
Skipjack tuna does not have a swim bladder.
Skipjack are at the top level of the pelagic food chain. Accordingly, fluctuations in their population size may significantly affect the balance of all trophic levels over time (Collette et al 2011). All tuna have the specialised anatomy of a vascular counter-current heat exchanger, that allows them to sustain muscle temperatures above ambient temperature, so enabling them to live in a wide range of temperatures. They regulate their body temperature in response to their muscle temperature changes, moving into cooler or warmer waters as needed. In this way, the feeding habitat of adult fish can be extended to the rich, deep forage layer, or to more productive temperate surface waters (Lehodey et al, 2011).
Habitat and Distribution
Skipjack live in offshore tropical and subtropical waters where they often school in surface waters with birds, drifting objects, sharks and whales (Collette, 2001). They range seasonally to 40°N and 40°S, roughly corresponding to the 20°C surface isotherm (Hoyle et al, 2011; Banks et al, 2011). Skipjack do not occur over shallow coastal shelves (ocean depths less than about 50 m) due to their need for access to warmer and cooler water. [See slide show for skipjack distribution map]
The availability of food, suitable water temperatures and dissolved oxygen levels, determine the distribution and abundance of skipjack. Except for the shallow coastal shelves, skipjack tuna live within a depth range of 0-260 m (Collette & Nauen, 1983) and sea surface temperature range of 17-30 degree C (Lehodey et al, 2011). In general, skipjack are less tolerant of low ambient oxygen concentrations than are yellowfin and bigeye tuna, and increase their swimming speeds when oxygen levels fall below 4 mg/l. Skipjack also spend less than 10% of their time at depths where oxygen levels are below ~ 5.0 mg/l (3.8 ml/l, 75% saturation) (Lehodey et al, 2011).
Skipjack movement is highly variable, being influenced by large-scale oceanographic variability. Skipjack also make long migrations into temperate waters during the summer months (Miyake et al, 2010). Tagging data show that individual skipjack are capable of undertaking long-distance movements of several thousand kilometres; and make significant seasonal movements between the western and eastern equatorial regions (Hoyle et al, 2011).
Growth, Reproduction and Diet
Skipjack growth is rapid compared to that of other large tunas. Females and males mature at 1-2 years, at size 40-45 cm (fork length) and are captured at sizes between 40 and 70 cm (WCPO) or 3.0-3.5 kg (IO) at 1-3 years of age.
If not captured, skipjack can grow to 100 cm fork length (FL), commonly to 80 cm FL. The maximum recorded weight is 34.5 kg (IO) (Collette & Nauen, 1983; Collette, 2001), and 30 kg (WCPO). The maximum reported age estimates vary at least between 8 and 12 years (Collette & Nauen, 1983) but most skipjack do not live beyond 3 to 4 years.
Skipjack are highly fecund and can spawn throughout the year in the tropics, although a study in the Indian Ocean revealed that the gonadosomatic index (GSI) is highest in January, April, July and December, and lowest in June and August (Norungee & Kawol, 2011).
Under favourable conditions, skipjack are serial opportunistic spawners. A skipjack releases its eggs in several portions; the eggs and the larvae are pelagic. The sex ratio does not appear to vary with size for skipjack (Hoyle et al, 2011) and (in the Indian Ocean), males are slightly more common (1.19:1) than are females (Norungee & Kawol, 2011).
Skipjack feed on fishes, crustaceans, cephalopods and molluscs; cannibalism is common (Collette, 2001). The principal predators of skipjack are other large pelagic fishes, including tunas and billfishes (Collette & Nauen, 1983).
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The information on skipjack was compiled and written by Patricia Kailola, and edited by Meryl Williams and Derek Staples.
Information Provided by the Following
- John Hampton (Secretariat for the Pacific Community -SPC)
- Johann D. Bell, SPC (Pacific Island consumption patterns, climate change)
- Lindsay Chapman, SPC (Pacific Island consumption patterns)
- Simon Hoyle – SPC
- Peter Williams – SPC
- Peter Nichols (CSIRO, Australia)
- Victor Restrepo ISSF
- Ludwig Kumoru – Papua New Guinea, National Fisheries Authority
- Leontine Baje – PNG NFA
- M. Shiham Adam – Maldives Marine Research Centre (and Founding Trustee of the International Pole-and-Line Foundation, IPNLF, http://www.ipnlf.org)
- FAO – for use of figures
- Fishbase team
- Victoria Jollands - updating Sustainability and Quick Facts pages, Feb. 2019
Drafts of the presentation were reviewed by the following:
- John Hampton (SPC)
- Victor Restreppo (ISSF, SAC Chair)
- Johann Bell (SPC)
- Lindsay Chapman (SPC)
- Meryl Williams (AsiaPacific-FishWatch)
Photographs and Graphics
- Secretariat for the Pacific Community
- Johann Bell (SPC)
- International Seafood Sustainability Foundation
- Fabien Forget (ISSF)
- David Itano (ISSF, personal)
- Food and Agriculture Organization
- Warren Scomi (SPC)
- Wikimedia Commons
Funding and Support
Funding to prepare the skipjack information was provided by the International Seafood Sustainability Foundation (iss-foundation.org) and the Asian Fisheries Society (www.asianfisheriessociety.org).
In-kind support has been provided by the host organizations of those who provided information and reviewed drafts.