Pacific Common Thresher Shark (Alopias vulpinus)

• Pacific thresher shark populations are estimated to be high, but it is unknown whether overfishing is occurring.
• In the Pacific Ocean, common thresher shark is managed by both the Pacific and Western Pacific Fishery Management Councils.
• Shark is high in protein and low in fat. It is a good source of niacin, vitamins B6 and B12, and phosphorus and a very good source of selenium. Shark may contain amounts of methylmercury in excess of the FDA's recommended limit for moms, moms-to-be, and young children. For more information, see EPA and FDA advice on what you need to know about mercury in fish and shellfish.
• About 90% of the thresher shark landed in the U.S. in 2006 were Pacific thresher shark; only about 10% were from the Atlantic fishery.

Sustainability Status

Biomass: Unknown; Unknown; preliminary analyses of common thresher shark catch in the pelagic drift gillnet fishery operating off the U.S. West Coast indicated that the biomass in 2000 was above the biomass supporting the maximum sustainable yield (MSY).
Overfishing: Unknown; preliminary analyses of common thresher shark catch and effort in the pelagic drift gillnet fishery operating off the U.S. West Coast indicated that the catch-per-unit-effort of thresher sharks was increasing in the late 1990s above historical lows experienced during the early 1990s. Thus, in the U.S. West Coast EEZ, overfishing is not occurring and populations are rebuilding.
Overfished: Unknown; see "Biomass" above
Fishing and habitat: The largest take of thresher sharks on the U.S. West Coast occurs in the pelagic drift gill net fishery which targets primarily swordfish. Small numbers of common thresher sharks are also landed by harpoon gear, in the set net fisheries which target halibut and angel sharks, and in the small mesh drift gillnet fishery which targets primarily seabass. In the western Pacific, common thresher sharks are occasionally caught using longlines, however this species is not encountered as frequently as the other two thresher species outside of 200 miles. In general, highly migratory species (HMS) fishing gear is not known to directly alter water column habitat because the approved gears that are used in the HMS fisheries do not contact the bottom substrate, but habitat can be affected by inadvertent loss of gear that is left to "ghost fish," and create marine debris that can cause harm to other species in the pelagic environment.
Bycatch: In both drift gill net and longline fisheries, bycatch of non-target species is a concern. Bycatch in the pelagic drift gill net fishery off the U.S. West Coast is mainly comprised of ocean sunfish and blue shark, although marine mammals and turtles are also occasionally taken. Fisheries regulations limiting both the season and geographic range of the pelagic drift-gill net fishery were implemented to reduce bycatch. NMFS is addressing the marine mammal interactions through the Pelagic Offshore Cetacean Take Reduction Plan. In the western Pacific both area closures and gear restrictions have helped minimize the bycatch of sharks and marlins, and have reduced protected species interactions. Longline vessels are required to employ special measures to avoid catching sea turtles and seabirds and increase the likelihood of their survival after release. Bycatch reduction is also achieved through non-regulatory means, including outreach to fishermen and engagement of fishermen in research activities and the management process. U.S. efforts to reduce bycatch on all fronts are ongoing, however fisheries outside of the U.S. may land thresher sharks in fisheries which do not employ comparable bycatch reduction strategies.
Aquaculture: There is currently no commercial aquaculture of thresher shark in the United States.

Science and Management

In federal waters off the West Coast, the common thresher shark is managed by the Pacific Fishery Management Council through the Fishery Management Plan for U.S. West Coast Fisheries for Highly Migratory Species (HMS FMP). Prior to that, thresher shark fisheries off the U.S. West Coast were managed by the states. The thresher shark drift gill net fishery developed in the late 1970s off California and the first substantial regulations impacting the drift gill net fishery off the U.S. West Coast were implemented in 1990 when both the season and range of the fishery were restricted, in part to reduce bycatch of protected species. In April 2005, new monitoring requirements came into effect with the implementation of the HMS FMP. The current regulations require that commercial fishermen obtain a permit from NMFS to fish for HMS and maintain logbooks documenting their catch. Recreational charter vessels must also keep logbooks. These measures are intended to improve data collection regarding HMS catches. There is also a recreational daily possession limit of two pacific common thresher sharks within the HMS FMP. A federal law prohibits "shark finning," where fins are removed and the carcass is discarded.

In the western Pacific, thresher sharks are managed by the Western Pacific Fishery Management Council through the Pelagics FMP, implemented in 1987. The FMP governs fishing activities of U.S. vessels and foreign vessels in the U.S. Exclusive Economic Zone (EEZ) with area closures, gear restrictions, fishing permits, reporting and observer requirements, submission of effort plans, and catch and effort limits. U.S. vessels in the western Pacific are prohibited from using drift gillnets unless they have an experimental fishing permit.

Because highly migratory species move throughout large areas of the Pacific and are fished by many nations and gear types, management by the United States alone is not enough to ensure that harvests are sustainable in the long term. While the common thresher is not managed internationally in the Pacific, as it is more abundant off coasts, the United States is participating in bilateral meetings regarding shark management with Japan, Spain, Taiwan, the European Union, Canada, China, and Mexico. Recent resolutions on shark conservation and management of the two international fisheries management organizations operating in the Pacific, the IATTC and WCPFC, may result in future monitoring and management of thresher and other pelagic sharks.

Researchers at NMFS Southwest Fisheries Science Center and Pacific Islands Fisheries Science Center are studying Pacific sharks, including the common thresher shark, to learn more about their biology, distribution, movements, stock structure and status, and potential vulnerability to fishing pressure. This information is provided to international, national, and regional fisheries conservation and management bodies charged with the sustainable management of pelagic sharks.

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: Common thresher sharks are distributed around the world in the Atlantic, Pacific, and Indian Oceans and in the Mediterranean.
• Habitat: Thresher sharks live in temperate and warm oceans but also penetrate into tropical waters. They are most abundant over continental and insular shelves and slopes. This species is often found in areas of high productivity where schooling pelagic prey are abundant.
• Life span: Maximum age is uncertain; estimates of maximum age vary from 19 to 50 years.
• Food: Thresher sharks have been observed to use their long caudal fin to bunch up, disorient and stun prey at or near the surface and are often caught on longlines tail-hooked. The main prey of the common thresher shark are small pelagic fish including anchovies, Pacific sardines, herring, and mackerel. Other species found in stomach contents of common thresher sharks, although less frequently, include Pacific hake, lancetfish, lanternfishes, Pacific salmon, squids, octopus, pelagic red crab, and shrimp.
• Growth rate: Slow
• Maximum size: 20 feet; approximately half of the body length consists of their tail.
• Reaches reproductive maturity: Both males and females mature at about 5 years of age when they are around 10 feet in length.
• Reproduction: Relative to other marine fish, sharks have a very low reproductive potential with common thresher sharks at the lower end of the spectrum Thresher sharks bear live young and a normal brood size is to be 2-4 pups. While in the uterus, the developing fetuses feed on yolk-filled egg capsules that are produced by the female. Gestation is about 9 months.
• Breeding season: Mating is thought to take place in the midsummer with pups born the following spring.
• Breeding and pupping grounds: In the eastern Pacific, mating occurs along U.S. West Coast. Pups are found from Monterey Bay and into Mexican waters along the Baja peninsula.
• Migrations: Thresher sharks are highly migratory species. They are pelagic, ranging widely in the upper zones of the oceans and can cross entire ocean basins. The majority of documented movements are, however, much shorter.
• Predators: Sharks are near the top of the food chain and, especially at larger sizes, have few predators other than humans.
• Commercial or recreational interest: Both
• Distinguishing characteristics: The common thresher shark is counter shaded similar to most pelagic predators. Their back and the underside of their snout is brown, gray, or purple, they are lighter on the sides and abruptly white below. A white area extends from the abdomen over the pectoral fin bases. The pectoral, pelvic, and dorsal fins are brown to gray, and white dots are sometimes present on pectoral, pelvic, and caudal fin tips. The caudal fin is sickle-shaped, and the upper lobe is extremely long, about 50% of total body length.

Role in the Ecosystem

As important predators in the world's oceans, sharks provide a valuable balance to the marine ecosystem. In ecosystems where sharks have been overfished large-scale ecological shifts have been documented. The greatest threat to sharks is over fishing, with estimates of over a hundred million sharks taken in fisheries per year. Other upper level predators, like killer whales and larger sharks may occasionally prey on small threshers. Concern about the status of many pelagic sharks is increasing.

Additional Information

Market name: Thresher Shark
Vernacular name: Fox Shark, Sea Fox, Swingletail, Whiptail Shark, Thintail Shark
Bigeye and pelagic thresher sharks are also marketed as Thresher Shark.

Biomass

Biomass refers to the amount of common thresher shark in the ocean. Scientists cannot collect and weigh every single shark to determine biomass, so they use 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. Although recent analyses indicate that the biomass of thresher sharks off the U.S. West Coast has been increasing since the early 1990s, estimates of biomass for thresher sharks are uncertain at this time.

Landings

Landings refer to the amount of catch that is brought to land. Off the Pacific coast, the drift gill net thresher shark fishery rapidly expanded from its initial development in the late 1970s, peaking in 1982, when 228 vessels landed more than 1,000 metric tons of shark. After this, catch declined and, swordfish replaced thresher shark as the primary target species of the drift gillnet fishery because there was a greater demand for swordfish and it commands a higher price-per-pound. Catch also declined due to the implementation of management measures to protect the thresher shark resource and associated bycatch species.

Note: Only domestic commercial landings are shown in the graph.

Biomass and Landings

Are landings and biomass related? Landings are dependent on biomass, management measures in the fishery, and fishing effort.

Data sources:
Landings from NMFS Annual Commercial Landings Statistics using "SHARK, THRESHER" as Species and "PACIFIC" as State

Important Dates

Late 1970s-1980s – A commercial drift gill net fishery for thresher shark develops off California and rapidly expands as market demands increase
1982 – Thresher shark fishery off the West Coast peaks at more than 1,000 metric tons (2.2 million pounds)
1987 – Western Pacific Fishery Management Council's Pelagics FMP implemented, with common thresher sharks one of the management unit species
1990 – Time and area restrictions for the U.S. West Coast drift gill net fishery reduce the effort on thresher sharks
2004 – Pacific Fishery Management Council's Highly Migratory Species FMP is implemented, with a harvest guideline imposed for common thresher sharks
2005 – New monitoring requirements established in Pacific under the PFMC FMP
2006 – IATTC and WCPFC pass resolutions on shark conservation and management calling for better research and periodic stock assessment efforts for the species of greatest concern

Notes and Links

General Information:
Southwest Fisheries Science Center Shark research page

NMFS Shark Web Site

Pacific Fishery Management Council's Background on Highly Migratory Species

Fishery Management:
Pacific Fishery Management Council Highly Migratory Species Fishery Management Plan

Western Pacific Fishery Management Council Pelagics FMP

Stock Assessments:
Status of the U.S. West Coast Fisheries for Highly Migratory Species through 2005