Atlantic Bigeye Tuna (Thunnus obesus)

• In 2007, NMFS updated the status of the Atlantic bigeye tuna stock, as Atlantic bigeye tuna abundance has stabilized near sustainable levels. While NMFS considers the bigeye stock to be no longer overfished and overfishing not occurring, Atlantic bigeye tuna remain a species of concern internationally given underreporting of landings. High levels of international cooperation are needed for appropriate management and conservation.
• Atlantic bigeye tuna is managed both domestically (by NMFS Highly Migratory Species Management Division) and internationally (by the International Commission for the Conservation of Atlantic Tunas and other organizations).
• Tuna is low in saturated fat and sodium and is a very good source of protein, thiamin, selenium, and vitamin B6. For more on nutrition, see Nutrition Facts. (USDA)
• Most of the bigeye tuna consumed in the United States is imported from Asia, South America, and Central America and is mainly from the Pacific Ocean.

Sustainability Status

Biomass: Atlantic bigeye tuna was last assessed in 2007. This assessment indicated that the stock declined rapidly during the 1990s due to the large catches made then, and that in recent years, it has stabilized at around or below sustainable levels in response to a large reduction in catches. Biomass in 2006 was 92% of the biomass needed to support maximum sustainable yield.
Overfishing: No
Overfished: No
Fishing and habitat: Bigeye tuna are caught by pelagic longline, baitboat, and purse seine in international fisheries, and primarily by longline and rod & reel in the U.S. fishery. Habitat damage by fishing gear used to capture highly migratory species, other than bottom longlines, is minor because it rarely comes in contact with the ocean floor.
Bycatch: Pelagic longline gear sometimes catches non-target finfish with little or no commercial value, as well as species that cannot be retained by commercial fishermen due to regulations, such as billfish. Pelagic longlines may also interact with protected species such as marine mammals, sea turtles, and seabirds. Area closures are used to minimize bycatch by closing ocean areas that historically have the highest rates of bycatch, and Vessel Monitoring Systems are required on U.S. Atlantic pelagic longline vessels to enforce closures and monitor the fishery. Circle hooks are also required to increase post-release survival of animals that are inadvertently caught. Additionally, U.S. Atlantic pelagic longline fishermen must attend workshops to learn how to properly handle and release these animals. The Atlantic, Caribbean, and Gulf of Mexico pelagic longline fishery is designated as a Category I fishery according to the List of Fisheries published annually by NMFS and required under the Marine Mammal Protection Act. This means that annual mortality and serious injury of certain marine mammal stocks in this fishery is greater than or equal to 50 percent of the Potential Biological Removal level (the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing it to be at sustainable levels). NMFS is addressing this challenge through the Pelagic Longline Take Reduction Team, which works to reduce serious injuries and mortalities of short-finned pilot whales, long-finned pilot whales, and Risso's dolphins in the Mid-Atlantic portion of the Atlantic pelagic longline fishery Bycatch of protected species by rod and reel is minimal.
Aquaculture: There is currently no commercial aquaculture of Atlantic bigeye tuna in the United States.

Science and Management

In the United States, Atlantic bigeye tuna is managed by the Highly Migratory Species (HMS) Management Division of NOAA's National Marine Fisheries Service through the Consolidated Atlantic Highly Migratory Species Fishery Management Plan. A minimum size restriction of 27 inches applies to all U.S. fisheries landing bigeye tuna, both commercial and recreational.

Atlantic HMS, such as bigeye tuna, are also managed internationally by the International Commission for the Conservation of Atlantic Tunas (ICCAT), of which the United States is a member. ICCAT conservation and management recommendations include total allowable catches, sharing arrangements for member countries, minimum size limits, effort controls, time/area closures, trade restrictions, compliance measures, and monitoring and inspection programs. The United States has authority to implement ICCAT's recommendations under the Atlantic Tunas Convention Act.

The United States also has responsibilities under the United Nations Agreement on the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks (known as the UNFSA). The United States is also a member of the Food and Agriculture Organization of the United Nations (FAO), which has implications for HMS management. In 1995, the FAO's Committee on Fisheries developed a Code of Conduct for Responsible Fisheries, which was adopted by more than 170 member countries, including the United States.

In 2007, the Standing Committee on Research and Statistics (SCRS) updated the Atlantic bigeye tuna assessment. The SCRS recommended that, to allow the stock to rebuild, a specific international cap on bigeye landings (85,000 metric tons) not be exceeded and reiterated its concern about unreported catches. It encouraged tuna Regional Fishery Management Organizations to examine the possibility of “fish laundering” (reporting landings as another species) for bigeye and other species.

Life History and Habitat

Life history, including information on the habitat, growth, feeding, and reproduction of a species, is important because it affects how a fishery is managed.

• Geographic range: Bigeye tuna is found in the Atlantic, Pacific, and Indian oceans in warmer temperature waters between 55 and 84º F. In the western Atlantic, they can be found from Nova Scotia to Argentina, including the Caribbean and the Gulf of Mexico.
• Habitat: Bigeye tuna are a pelagic species - they are found from the surface to about 800 feet deep. Larvae are found in tropical waters, but as juvenile fish grow larger, they tend to move into temperate waters.
• Life span: Bigeye tuna can live longer than 9 years.
• Food: Bigeye tuna feed at night and during the day on fishes, squid, and crustaceans found from the surface to a depth of 500 feet. They favor shrimp, mackerel, and other small tuna.
• Growth rate: Relatively fast.
• Maximum size: Bigeye typically range in length from 1.5 to 5.5 feet. Bigeye over 6.5 feet are rare.
• Reaches reproductive maturity: At about age three and a half.
• Reproduction: Mature bigeye spawn at least twice a year. Females can have from 2.9 million to more than 6 million ova. The Gulf of Guinea is a major nursery ground for Atlantic bigeye.
• Spawning season: Throughout the year when the environment is favorable, and peaking in summer months.
• Spawning grounds: In tropical waters.
• Migrations: Bigeye tuna are highly migratory. Juvenile and small adult bigeye tuna form schools mostly mixed with other tunas such as yellowfin and skipjack, especially in warm waters. These schools are often associated with drifting objects, whale sharks, and sea mounts.
• Predators: The main predators of bigeye tuna are large billfish and toothed whales.
• Commercial or recreational interest: Both
• Distinguishing characteristics: Bigeye tuna is dark metallic blue on the back and upper sides with white lower sides and belly. The first dorsal fin is deep yellow, the second dorsal and anal find are brownish or yellowish with narrow black edges, and the finlets are bright yellow with broad black edges. Their bodies are stocky and robust, and adults' eyes are large.

Role in the Ecosystem

Bigeye tuna are towards the top of the food chain and prey upon many aquatic species, such as fish, cephalopods, and crustaceans. They are also prey for top predators such as sharks.

Additional Information

Market name: Tuna
Vernacular names: Big Eye, Ahi-b

Biomass

Biomass refers to the amount of Atlantic bigeye tuna in the ocean. Scientists cannot collect and weigh every single fish to determine biomass, so they use mathematical models to estimate it instead. These biomass estimates can help determine if a stock is being fished too heavily or if it may be able to tolerate more fishing pressure. Managers can then make appropriate changes in the regulations of the fishery.

According to the most recent stock assessment in 2007, the biomass estimate for Atlantic bigeye tuna was 92% of maximum sustainable yield and has generally been stable since the year 2000.

Landings

Landings refer to the amount of catch that is brought to land. The total annual catch of Atlantic bigeye tuna increased up to the mid-1970s, peaking at 60,000 metric tons, and fluctuated over the next 15 years. In 1991, catch surpassed 95,000 metric tons and continued to increase, reaching an historic high of about 132,000 metric tons in 1994. Reported and estimated catch has been declining since then, falling below 100,000 metric tons in 2001, and was 76,000 metric tons in 2006, the lowest recorded level since 1988. After the historic high catch in 1994, catch in all major fisheries declined but the relative share by each fishery in total catch remained about the same. Catch declined due to reductions in fishing fleet size in the purse seine and longline fisheries as well as declines in the catch rate in the longline and baitboat fisheries. The activities of illegal, unreported and unregulated (IUU) longliners that fly flags of convenience appear to have started in the early 1980s, and became significant thereafter.

U.S. landings of Atlantic bigeye tuna have historically represented a small fraction (1% or less) of total Atlantic bigeye landings. Landings for 2005, 2006, and 2007 were 484, 987, and 523 metric tons, respectively.

Note: Only U.S. landings are shown in the graph.

Biomass and Landings

Landings and biomass data can sometimes be used to detect trends in a fishery. There does not seem to be much of a trend in U.S. bigeye tuna landings, or in the biomass of the population since 2000. This may indicate that current fishing effort might be at a level that allows the Atlantic bigeye tuna population to maintain its current biomass level. Although, other factors, such as changes in management measures, market preferences, and environmental conditions, may impact landings and biomass as well. Also, because bigeye tuna is a highly migratory species that moves outside of U.S. waters, fishing practices of foreign countries could affect U.S. Atlantic bigeye tuna landings and the biomass of the population.

Data sources:
Biomass and landings from 2007 ICCAT Bigeye Tuna Stock Assessment, 2008 U.S. National Report to ICCAT

Important Dates

1960s – Pelagic longline fishery for Atlantic tunas develops rapidly (comprised mainly of Japanese vessels fishing for swordfish and yellowfin tuna in the Gulf of Mexico)
1966 – International Convention for the Conservation of Atlantic Tunas is signed creating the International Commission for the Conservation of Atlantic Tunas (ICCAT)
1979 – ICCAT adopts a minimum size of 7 pounds with a 15% tolerance level for undersized bigeye tuna
1990 – Magnuson Act amended, giving authority to Secretary of Commerce to manage Atlantic tunas; secretarial authority is delegated to NMFS
1992 – NMFS creates the HMS Management Division to manage Atlantic tunas, sharks, swordfish, and billfish
1995 – ICCAT urges countries to reduce catches below MSY and reduce catches of undersized fish due to large increases in longline and purse seine catches of bigeye and the large number of undersize fish; also asks countries with equatorial fisheries catching undersized fish to place observers on the vessels and allow the Standings Committee on Research and Statistics (SCRS) to study the data
1997 – ICCAT issues two resolutions to limit the catch of larger vessels in the Atlantic and the catch of countries that caught more than an average of 200 metric tons between 1992 and 1996 and to collect information on the larger vessels in the fleet
1998 – ICCAT adopts two new management recommendations designed to limit effort in commercial fisheries for bigeye throughout the Atlantic
1998 – ICCAT adopts resolution tasking SCRS with developing stock rebuilding scenarios for bigeye
1999 – NMFS publishes the Final Fishery Management Plan (FMP) for Atlantic Tunas, Swordfish, and Sharks, the first FMP for Atlantic tunas; measures include prohibition of pelagic driftnets for tunas, implementation of the ICCAT Rebuilding Program for Western bluefin tuna
2003 – ICCAT recommends that each participating fishing nation limit its catch to the average taken over the years 1991 and 1992.
2004 – ICCAT recommends a four-year management and conservation program (for 2005-2008), including a limit on vessels and a 90,000 metric ton Total Allowable Catch
2006 – Consolidated Atlantic Highly Migratory Species Fishery Management Plan is approved and implemented; combines the management of all Atlantic HMS into one comprehensive FMP; also allows the use of speargun gear in Atlantic tuna recreational fisheries and shifts the fishing year to a calendar year for all HMS species
2008 – NMFS authorizes the use of green-stick gear to harvest Atlantic tunas

Notes and Links

General Information:
2007 Annual Report of the United States to ICCAT

South Atlantic Fishery Management Council Fish ID and Regulations - Bigeye Tuna

NMFS Guide to the Tunas of the Western Atlantic Ocean

Fishery Management:
Atlantic Highly Migratory Species Fishery Management Plans

Stock Assessments:
Atlantic Highly Migratory Species SAFE Reports

ICCAT Report 2006-2007 Bigeye Tuna

Report of the 2007 ICCAT Bigeye Tuna Stock Assessment Session

ICCAT 2007 Report of the Standing Committee on Research and Statistic (Stock assessment update)