Atlantic Skipjack Tuna (Katsuwonus pelamis)

• Population status is believed to be stable according to the most recent stock assessment (2008).
• Atlantic skipjack tuna are 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).
• Skipjack is an excellent source of low-fat protein. For more information, see Nutrition Facts. (USDA)
• Skipjack are primarily sold to the canning market.

Sustainability Status

Biomass: Unknown
Overfishing: Unknown
Overfished: Unknown
Fishing and habitat: Habitat damage by highly migratory species fishing gear used to catch skipjack tuna in the U.S. Atlantic fishery is minor because pelagic fishing gear rarely comes in contact with the ocean floor.
Bycatch: In the U.S. Atlantic skipjack tuna fishery, the majority of commercial landings come from vessels using handgear. Recreational fisherman mainly use rod and reel gear. There is little to no bycatch in either of these fisheries.
Aquaculture: There is currently no commercial aquaculture of skipjack tuna in the United States.

Science and Management

In the Atlantic, skipjack tuna is managed by NOAA's National Marine Fisheries Service (NMFS) Highly Migratory Species Management Division under the Consolidated Atlantic Highly Migratory Species (HMS) Fishery Management Plan. In the United States, skipjack tuna is captured with rod and reel and handgear. The U.S. Atlantic tuna commercial handgear fisheries are managed through an open access vessel permit program. Vessels that wish to sell their Atlantic tunas must obtain a commercial handgear permit.

Atlantic HMS, such as skipjack tuna, are also managed internationally by the International Commission for the Conservation of Atlantic Tunas (ICCAT), of which the U.S. 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 measures, compliance measures, and monitoring and inspection programs. The United States has authority to implement recommendations it accepts under the Atlantic Tunas Convention Act. No specific ICCAT regulation is in effect for skipjack tuna, but a voluntary moratorium on fishing with fish aggregating devices (FADs) has been recommended by ICCAT since 1999.

The United States 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.

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: Skipjack tuna form schools in the surface water of tropical, subtropical, and warm temperate waters of all oceans. In the Atlantic, skipjack is found from Massachusetts to Brazil, including the Gulf of Mexico and the Caribbean.
• Habitat: Skipjack tuna are a pelagic species, which means they mostly live in the open ocean, although they may spend part of their life cycle in nearshore waters. They are found in surface waters and to depths of 850 feet during the day, but seem to stay near the surface at night. Groups of skipjack tuna tend to be associated with convergence zones, boundaries between cold and warm water masses (i.e. the polar front), upwelling, and other hydrographical discontinuities.
• Life span: Maximum age is around 7 years.
• Food: Skipjack tuna are opportunistic foragers. They feed on fishes, crustaceans, cephalopods, and mollusks. Cannibalism is also common.
• Growth rate: Rapid
• Maximum size: The maximum reported size of a skipjack tuna is about 3.3 feet, and the maximum weight is about 41 pounds.
• Reaches reproductive maturity: Skipjack mature early. In the East Atlantic, females first mature at about 16.5 inches and males mature at 17.7 inches. In the West Atlantic, females mature at 20.1 inches and males mature at 20.5 inches. Skipjack are estimated to be about 1 year old or less at this size.
• Reproduction: Females produce between 100,000 to 2 million eggs per spawning event, depending on the size of the fish. Once fertilized, eggs hatch in about 1 day (depending on temperature). Skipjack spawn more than once a season, as often as every 1.18 days.
• Spawning season: Skipjack tuna spawn throughout the year in tropical waters and seasonally, spring to early fall, in subtropical areas.
• Spawning grounds: In the tropics, eggs are released in several portions of the ocean.
• Migrations: Skipjack tuna is a highly migratory species, which means it has a wide geographic distribution. The species undertakes migrations of significant but variable distances across oceans for feeding and reproduction.
• Predators: Skipjack tuna are preyed upon by large pelagic fishes such as billfish, sharks, and other large tunas. Humans are also predators of skipjack tuna.
• Commercial or recreational interest: Both
• Distinguishing characteristics: Skipjack tuna do not have scales except on the corselet and the lateral line. Their back is dark purplish blue, and the lower sides and belly are silvery with 4 to 6 very conspicuous longitudinal dark bands, which may look like continuous lines of dark blotches.

Role in the Ecosystem

The skipjack tuna life cycle progresses through four ecologically different phases. During spawning (in equatorial or warm tropical water) buoyant eggs are released and float at the surface where they become part of the zooplankton and food for the many small organisms and fish feeding in the equatorial surface waters. Within a day, the eggs hatch and the larval fish begin feeding on the same zooplankton that they are a part of. After 2-3 weeks, fully formed juveniles begin eating small fish, crustaceans, and mollusks. These juveniles also begin directed movement north and south of equatorial waters and are often preyed upon by larger tunas and billfish. After about one year, the adult skipjack has become an opportunistic predator with a highly varied diet and is now prey to not only larger tunas and billfish, but also to human fisheries activity.

Additional Information

Market name: Tuna
Vernacular names: Ocean Bonito, Lesser Tuna, Aku
Several other species are also marketed as Tuna.

Biomass

Biomass refers to the amount of skipjack 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. The biological characteristics of West Atlantic skipjack tuna make it extremely difficult to conduct a traditional assessment. Therefore, biomass, relative fishing mortality, and maximum sustainable yield levels have not been estimated.

Landings

Landings refer to the amount of catch that is brought to land. Skipjack tuna are caught by U.S. vessels in the western North Atlantic. The U.S. landings of western Atlantic skipjack tuna has historically accounted for a small percentage of the total international landings from that stock. In 2007, the U.S. contributed less than 0.26% of the total western Atlantic skipjack landings reported to ICCAT, with the majority of the 66.4 metric tons (77.5%) landed by the U.S. with rod and reel gear.

Note: Total U.S. landings (commercial and recreational) are shown in the graph.

Biomass and Landings

Landings and biomass data can sometimes be used to detect trends in a fishery. Because there is no biomass data for West Atlantic skipjack tuna, it is difficult to determine what effect commercial landings are having on the population. Landings have remained at low levels, which may be the result of factors, such as management measures, market preferences, or environmental conditions. Skipjack tuna is a highly migratory species that moves outside of U.S. waters, therefore fishing practices of foreign countries could affect U.S. West Atlantic skipjack tuna landings and the biomass of the population. Also, recreational fishing efforts may impact skipjack tuna populations.

Data sources:
Landings from ICCAT 2008 Report of the Standing Committee on Research and Statistic (Stock assessment update), 2008 U.S. National Report to ICCAT

Important Dates

1966 – International Convention for the Conservation of Atlantic Tunas is signed creating the International Commission for the Conservation of Atlantic Tunas (ICCAT)
1980s – Atlantic HMS managed by regional fishery management councils
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
1997-2002 – Voluntary moratorium on fishing with FADs applied
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.
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:
NMFS Office of Sustainable Fisheries Highly Migratory Species Division

Fishery Management:
NMFS Office of Sustainable Fisheries Highly Migratory Species Division - Tunas

Stock Assessments:
ICCAT 2008 Report of the Standing Committee on Research and Statistic (Stock assessment update)

2007 Stock Assessment and Fishery Evaluation Report for Atlantic HMS