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 in Table D19. It was obtained by interpreting results of stock assessments according to the classification procedure adopted by FAO in this review. Those assessments available at the time of preparation of this review (end of March 2011) were taken mostly from Web pages of:

• Commission for the Conservation of Southern Bluefin Tuna (CCSBT );
• Inter-American Tropical Tuna Commission (IATTC ) for the eastern 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 than those for other species of tuna and tuna-like species. They have been studied for many years 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 of the best studied tuna, may be considerably longer than previously believed. Moreover, for this species, as compared with trade statistics, the catches were substantially under reported for a number of years. For Atlantic bluefin tuna, another well-studied species, officially reported catches might be significantly smaller in the past than those actually taken. This conclusion is based on information from a trade-based statistical programme introduced by ICCAT (Miyake, 1998) as well as from capacity estimates (ICCAT, 2009). When considering the information on the stock status, uncertainties in stock assessment need to be taken into account.

Most tuna stocks are fully exploited, some are overexploited. Generally, some temperate 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 the Pacific bluefin (also used for sushimi), the yield-per-recruit could be increased if the number of small bluefin caught by trolling and purse seining can be reduced.

The stocks of albacore (temperate species) used mostly for canning are not fully exploited in the South Pacific but they are fully exploited in the Indian Ocean and the South Atlantic and overexploited in the North Atlantic and the North Pacific. The status of albacore in the Mediterranean Sea is unknown.

Generally, most tropical principal market tunas have reacted well to exploitation owing to their very high reproductive potential, wide geographical distribution, opportunistic behaviour and other population dynamics characteristics that make them highly productive. With proper management, they are capable of sustaining high yields.

There may still be potential for increasing catches of skipjack in the western and central Pacific with lower potential in the other oceans. However, skipjack are caught together with tuna species that are fully exploited or overexploited. Therefore, until more selective fishing methods are developed, it is not desirable to increase the catches of skipjack.

Most other stocks of tropical tunas have become fully exploited and a few are overexploited. Generally, a possibility of further deterioration in the status of tropical tunas should not be underestimated. Concerns are increasing over the exploitation of bigeye in all oceans. This is another species that is highly desired for sashimi and has a shorter 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 per recruit.

The status of many tuna and tuna-like species other than the principal tunas is highly uncertain or simply unknown. Therefore, the intensification of their exploitation raises concerns. Significant uncertainties in the status of many billfishes represent a serious conservation problem. Some stocks are overexploited in the Atlantic and the Pacific, while their status is mainly unknown in the Indian Ocean. Because of commercial exploitation, there is more known about swordfish than other billfishes. In the Mediterranean Sea, the swordfish stock seems to be overexploited, but the overall situation in the remainder of the Atlantic and Pacific is more optimistic. However, in the Indian Ocean, there are concerns about the intensification of swordfish fishing owing to the risk of potential local overexploitation.