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An Assessment of Atlantic Bluefin Tuna 1 Background Atlantic bluefin tuna (Thunnus thynnus) are prized catches of both recreational and commercial fishermen. These fish are migratory and are known to traverse the Atlantic Ocean in a few months. Bluefin tuna are among the largest bony fish in the ocean, reaching over 10 feet (3.05 meters) in length and over 1,200 pounds (544 kilograms) in weight. Their lifespans can exceed 30 years, making them long lived among fish species. The popularity of bluefin tuna, as demonstrated by the historic international fishery, has contributed to the significant exploitation of this species, especially in the North Atlantic Ocean. Furthermore, the high selling price of high-quality bluefin tuna on the raw seafood market in Japan has provided a financial incentive for the expenditure of great effort to pursue and catch these fish. The need for coordinated international management of highly migratory fish species in the Atlantic Ocean was recognized in the mid-1960's, leading to the International Convention for the Conservation of Atlantic Tunas, signed on May 14, 1966. The convention is implemented by an international body called the International Commission for the Conservation of Atlantic Tunas (ICCAT), presently consisting of 22 member nations, including the United States, Canada, Japan, Spain, and France. The headquarters for ICCAT is in Madrid, Spain. ICCAT is responsible for providing internationally coordinated research on the condition of the Atlantic tunas and related species (e.g., swordfish) and their environment, as well as for the development of regulatory harvest proposals for consideration by the member nations. The objective of the regulatory proposals is to conserve and manage tuna and related species throughout their ranges in a manner that achieves the maximum sustainable catch.
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An Assessment of Atlantic Bluefin Tuna The U.S. law implementing the convention is the Atlantic Tunas Convention Act of 1975 (ATCA). ATCA stipulates that the United States shall be represented in ICCAT by not more than three commissioners who are appointed by the President and who can serve no more than two three-year terms. One of the three U.S. commissioners can be a salaried government employee. To date, an official from the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) always has served as one of the U.S. commissioners. Of the other two, who are not employed by the government, one must be knowledgeable and experienced with regard to commercial fishing in the Atlantic Ocean, Gulf of Mexico, or Caribbean Sea, whereas the other is required to be knowledgeable and experienced with regard to recreational fishing in one of these regions. The U.S. commissioners are assisted by an advisory committee consisting of between five and 20 individuals who are selected from the various groups concerned with fisheries that are governed by the convention. The advisory committee has the opportunity to offer comments on all proposed programs of investigation, reports, recommendations, and regulations of the commission. ICCAT has four components: (1) the commission (composed of not more than three delegates from any member nation); (2) the council (an elected body with a chairman, vice-chairman, and representatives from four to eight member nations that performs functions assigned to it by the convention or commission); (3) the executive secretary (responsible for commission finances, coordinating ICCAT programs, preparing the collection and analysis of data to accomplish the purposes of the convention, and preparing reports for approval by the commission); and (4) subject area panels (established by the commission and responsible for reviewing the species under their purview, collecting scientific and other information, proposing recommendations for joint actions, and recommending studies by member nations). Standing Committees on Research and Statistics (SCRS) have been established by the commission. The commission is responsible for formulating regulatory proposals, which are approved by ICCAT and submitted to member governments for approval. If there are no objections from any concerned contracting government within approximately six months, each party to the convention is then responsible for implementing and enforcing the regulations recommended by ICCAT. ICCAT REGULATIONS FOR ATLANTIC BLUEFIN TUNA In 1974, ICCAT recommended the first regulatory measures for Atlantic bluefin tuna. These measures included a minimum size limit of 6.4 kg and a limit on fishing mortality to the levels of 1974. In 1981, ICCAT adopted the premise of a two-stock structure for Atlantic bluefin tuna, one in the eastern and the other in the western Atlantic Ocean. Also in 1981 the capture of bluefin tuna in the western Atlantic Ocean was prohibited, except for a catch quota established
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An Assessment of Atlantic Bluefin Tuna specifically for continuing scientific monitoring of the western stock. This scientific catch was allocated to ICCAT-participating nations that had active fisheries (including the United States, Canada, and Japan). Brazil and Cuba were exempted from the regulations because their total catches were small (less than 50 metric tons). For the 1983 fishing season in the western North Atlantic Ocean, ICCAT established a total allowable catch of 2,660 metric tons. ICCAT also limited the catch of smaller fish, less than 120 cm in length, to no more than 15% in weight of the catch limit for the western stock. In addition, spawning areas such as the Gulf of Mexico were protected by prohibiting any directed fishery there. In each year from 1983 to 1991, ICCAT approved a one-year extension of the existing management measures for both stocks of bluefin tuna. During the 1991 ICCAT meeting, new regulations were recommended to reduce the western stock's scientific monitoring quota by 10% in 1992 and again in 1993, with the possibility of additional reductions of up to 25% based on future SCRS analyses. Other measures were adopted by ICCAT at the 1991 meeting, including limiting catches of small fish, penalties for exceeding quotas, promoting tag and release efforts, and a bluefin tuna documentation and reporting program phasing in. Exporters of bluefin tuna will be required to provide documents that identify the location and nation of the vessel that caught the fish. To date, ICCAT has not recommended a quota for the eastern stock. However, measures for catch size limits and protection of spawning areas have been implemented for the eastern stock. ISSUES IN ATLANTIC BLUEFIN TUNA MANAGEMENT ICCAT management for Atlantic bluefin tuna has evolved according to the premise of a two stock structure that can be managed independently. Implementation of this assumption began in member nations in 1982. Since 1991, each stock has been alternately reviewed every second year by the commission. Because of the perceived decline in abundance of western Atlantic bluefin tuna, the two stocks have been subject to different regulations, the most striking difference being the lack of a quota for the eastern stock fishery and the imposition of a strict scientific quota only for the western stock fishery. The two most contentious issues concerning the management of Atlantic bluefin tuna are the definitions and sizes of management units and the indices of abundances that are now used to calculate stock assessments. Opposition to managing the western and eastern Atlantic bluefin tuna stocks as separate units has arisen primarily from lack of definitive scientific evidence for genetically-discrete populations, and alternative population structures have been suggested. The implications for management are significant-if there are more or fewer populations, the present ICCAT management, including the regulations, would have to be modified and new regulations agreed to by all member nations.
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An Assessment of Atlantic Bluefin Tuna PURPOSE OF THIS STUDY The 1994 ICCAT meeting is scheduled for November in Madrid, Spain. Most management efforts will focus on the eastern stock, because this is its year for assessment. The western stock will be assessed at the 1995 ICCAT meeting. However, new measures could be recommended for the western stock in 1994 and for the eastern stock in 1995. The National Research Council's Ocean Studies Board received a written request from NOAA (dated January 26, 1994) to conduct a peer review study within six months so as to enable NOAA to use the results for the 1994 ICCAT meeting. Accordingly, the Ocean Studies Board established the Committee to Review Atlantic Bluefin Tuna to review and evaluate the scientific basis of U.S. management of fisheries for Atlantic bluefin tuna and to recommend research to resolve remaining stock structure issues. Members chosen for the committee have a range of expertise, including tuna biology and physiology, fish genetics and stock identification, fish population dynamics, fish ecology, and oceanography (see Appendix A). A notice soliciting comments from the public regarding scientific issues for consideration by the review committee was published in the Federal Register.1 Numerous comments were received, and at the first committee meeting, in May 1994, individuals who had submitted written comments were invited to give a brief presentation to the review committee. The committee met again in June 1994 to hear additional individuals and to complete this report. In addition, the committee reviewed extensive peer-reviewed and gray scientific literature (see Appendix B) as background for its deliberations. This report focuses primarily on the scientific basis for (1) the assumptions about stock structure and (2) indices of abundances used in the stock assessments for western Atlantic bluefin tuna. The issue of stock structure of Atlantic bluefin tuna is discussed in Chapter 2, and movement of Atlantic bluefin tuna is discussed in Chapter 3 . Information on the indices of abundances and the results of sensitivity analyses conducted by the committee using data sets obtained from NOAA's National Marine Fisheries Service and the industry are presented and discussed in Chapter 4. In Chapter 5 the committee summarizes its major findings and makes general recommendations and research recommendations for improving the scientific basis of the management of Atlantic bluefin tuna. 1 Federal Register, March 3, 1994, vol. 59, no. 42, pp. 10114-10115.
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