Habitat and Biology
Climatic zone: Temperate; Tropical.
Information on the habitat and biology of tunas and tuna like species is further described in the factsheet on the Biological characteristics of tunas and tuna-like species
and in Goujonand Majkowski (2010). Global aspects of tuna resources, fishing, fisheries management,processing and trade can be found in Allen (2010), Joseph (1998, 2000, 2003), Miyake,Miyabe and Nakano (2004) and Miyake et. al. (2010). Information references at regionalscale are given in the respective sections on resource status.
Jurisdictional distribution: Highly migratory
The 1982 UNCLOS classifies the principal market tunas, billfishes, blackfin tuna,bullet and frigate tuna, little tunny and kawakawa as highly migratory. This is despitelittle tunny and kawakawa being mostly confined to the continental shelf and upperslope. Black skipjack is not classified as highly migratory, but it is probably moreoceanic than little tunny and kawakawa.
Considered a single stock: No
The suborder Scombroidei is usually referred to as tuna and tuna-like species (Klawe,1977; Collette and Nauen, 1983; Nakamura, 1985). It is composed of tunas (sometimesreferred to as true tunas), billfishes and other tuna-like species. They include some ofthe largest and fastest fishes in the sea. The tunas are classified into 5 genera (Thunnus
) with 15 species all together.
The most economically important tuna species on the global scale are referred to asprincipal market tunas. From the genus Thunnus
, they include albacore (T. alalunga
),Atlantic bluefin tuna (T. thynnus
), bigeye tuna (T. obesus
), Pacific bluefin tuna(T. orientalis
), southern bluefin tuna (T. maccoyii
) and yellowfin tuna (T. albacares
).Skipjack tuna (Katsuwonus pelamis
) is the seventh principal market tuna species. Theyare subject to intensive international trade for canning and sashimi (raw fish regarded asa delicacy in Japan and, increasingly, in many other countries).
The efficient physiology of principal market tunas allows them to retain or dissipateheat as required for peak biological performance and efficiency. They are all oceanic(Figure C1.1), capable of long migrations or movements, but not necessarily all speciesre-distribute or mix well within the areas of their stocks’ distribution. Most speciesconstitute one or two stocks in each ocean, although the albacore in the Atlantic consistsof three stocks (including that in the Mediterranean Sea). The exceptions are Atlanticand Pacific bluefins, which occur only in their eponymous oceans. Southern bluefinconstitute a single stock extending in the Atlantic, Indian and Pacific Oceans.
The tunas other than the principal market species are more neritic (living in watermasses over the continental shelf). They include longtail tuna, blackfin tuna (T. atlanticus
),black skipjack (E. lineatus
), kawakawa (E. affinis
), little tunny (E. alleteratus
), bullettuna (A. rochei
) and frigate tuna (A. thazard
The billfishes (Istiophoridae) are composed of marlins (Makaira
spp.), spearfish (Tetrapturus
spp.) and swordfish (Xiphias gladius
, onlyspecies in the genus). With the exception of two species (Mediterranean and roundscalespearfish), all billfishes have very wide geographical distributions, but not all speciesoccur in all oceans. Billfishes are mostly caught by longlines as bycatch. The exceptionsare swordfish, which are targeted in certain regions with longlines and harpoons.Billfishes are also taken in sport fisheries, where they are greatly valued. They are allconsidered excellent eating.
Other important tuna-like species include slender tuna (Allothunnus fallai
), butterflykingfish (Gasterochisma melampus
), wahoo (Acanthocybium solandri
), Spanish and king mackerels, seerfish and sierra(Scomberomorus
spp.). They and other tuna-like species are all the object of fishing.They have a significant fishery potential, especially for developing countries wheremostly artisanal and recreational fisheries are now catching them. Slender tuna andbutterfly kingfish (with a circumpolar distribution in the Southern Ocean) are nowcaught mostly as bycatch of the Japanese longline fishery targeting southern bluefintuna.
|Figure C1.1 Distribution of principal market tunas and fishing areas |
Information on fishery are available at the following link: World oceans Global Tuna fisheries
Biological State and Trend
PRINCIPAL MARKET TUNAS
The following classification of the status of stocks is used throughout this document.
- U Non-fully exploited.
- F Fully exploited.
- O Overexploited.
For Further clarifications on the criteria for the classification of fish stock status, see the Source Report (Appendix - Assessment methodology, Table 1)
A summary on the status of various stocks of tuna and tuna-like species is given inTable D19. It was obtained by interpreting results of stock assessments according to theclassification procedure adopted by FAO in this review. Those assessments availableat the time of preparation of this review (end of March 2011) were taken mostly fromWeb pages of:
- Commission for the Conservation of Southern Bluefin Tuna (CCSBT );
- Inter-American Tropical Tuna Commission (IATTC ) for theeastern Pacific;
- International Commission for the Conservation of Atlantic Tunas (ICCAT );
- Indian Ocean Tuna Commission (IOTC );
- Western Central Pacific Fishery Commission (WCPFC ).
The knowledge and data on the principal market tunas are generally much better thanthose for other species of tuna and tuna-like species. They have been studied for manyyears and more research effort is devoted to them. However, even for these species,significant uncertainties exist in the basic biological knowledge and data. For example,relatively recent research indicates that the life span of southern bluefin tuna, one ofthe best studied tuna, may be considerably longer than previously believed. Moreover,for this species, as compared with trade statistics, the catches were substantiallyunder reported for a number of years. For Atlantic bluefin tuna, another well-studiedspecies, officially reported catches might be significantly smaller in the past than thoseactually taken. This conclusion is based on information from a trade-based statisticalprogramme introduced by ICCAT (Miyake, 1998) as well as from capacity estimates(ICCAT, 2009). When considering the information on the stock status, uncertainties instock assessment need to be taken into account.
Most tuna stocks are fully exploited, some are overexploited. Generally, sometemperate tuna species (i.e. Atlantic and southern bluefins [most desired for sashimi])are much more overexploited (depleted) than any of the tropical tuna species. For thePacific bluefin (also used for sushimi), the yield-per-recruit could be increased if thenumber of small bluefin caught by trolling and purse seining can be reduced.
The stocks of albacore (temperate species) used mostly for canning are not fullyexploited in the South Pacific but they are fully exploited in the Indian Ocean and theSouth Atlantic and overexploited in the North Atlantic and the North Pacific. Thestatus of albacore in the Mediterranean Sea is unknown.
Generally, most tropical principal market tunas have reacted well to exploitationowing to their very high reproductive potential, wide geographical distribution,opportunistic behaviour and other population dynamics characteristics that make themhighly productive. With proper management, they are capable of sustaining high yields.
There may still be potential for increasing catches of skipjack in the western andcentral Pacific with lower potential in the other oceans. However, skipjack are caughttogether with tuna species that are fully exploited or overexploited. Therefore, untilmore selective fishing methods are developed, it is not desirable to increase the catchesof skipjack.
Most other stocks of tropical tunas have become fully exploited and a few areoverexploited. Generally, a possibility of further deterioration in the status of tropicaltunas should not be underestimated. Concerns are increasing over the exploitation ofbigeye in all oceans. This is another species that is highly desired for sashimi and has ashorter life span than bluefin. In addition to possibly causing overfishing in the future,the increasing purse seine catches of small bigeye may negatively affect the yield perrecruit.
The status of many tuna and tuna-like species other than the principal tunas is highlyuncertain or simply unknown. Therefore, the intensification of their exploitationraises concerns. Significant uncertainties in the status of many billfishes represent aserious conservation problem. Some stocks are overexploited in the Atlantic andthe Pacific, while their status is mainly unknown in the Indian Ocean. Because ofcommercial exploitation, there is more known about swordfish than other billfishes. Inthe Mediterranean Sea, the swordfish stock seems to be overexploited, but the overallsituation in the remainder of the Atlantic and Pacific is more optimistic. However, inthe Indian Ocean, there are concerns about the intensification of swordfish fishingowing to the risk of potential local overexploitation.Table D19: State of exploitation and annual nominal catches of tuna and tuna-like species in all Oceans, 1950–2009.
Source of information
Marine and Inland Fisheries Service, Fisheries and Aquaculture Resources Use and Conservation Division. FAO Fisheries and Aquaculture Department “Review of the state of world marine fishery resources”
. FAOFISHERIES ANDAQUACULTURETECHNICALPAPER.
No. 569. Rome, FAO. 2011. http://www.fao.org/docrep/015/i2389e/i2389e.pdf
The bibliographic references are available through the hyperlink displayed in "Source of Information".ACKNOWLEDGEMENTS
The authors are grateful to Dr Peter Miyake and his colleagues for their help withthe provision of information for the preparation of the section ob Fisheries and TableC1.1. They also appreciate the assistance of the Secretariats and tuna scientists of FFA,t-RFMOs and SPC with obtaining information for this review and their cooperation andcollaboration with FAO. Drs Robin Allen and Victor Restrepo have kindly providedhelpful suggestions for improving an earlier version of this review.