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Overview

Brief Summary

Biology

The thresher shark is an active strong-swimming fish that is occasionally seen leaping out of the water (2). It feeds primarily on small, schooling fish, but also fish that dwell on the ocean bottom, squids, octopi and, very rarely, seabirds (2). It uses its unique tail fin to herd fish together in tight shoals, and then stuns them with powerful swipes of the tail. Sometimes two threshers may cooperate in their attack, swimming round the school of fish in ever decreasing circles, then striking the shoal with their tails before turning to swallow their stunned or dead victims (2) (3). Thresher sharks possess some remarkable physiological adaptations which explain their strength and endurance in a wide range of latitudes and depths. Along each of their flanks runs a strip of red muscle, which can contract powerfully for long periods, enabling the thresher shark to swim for long periods without fatigue (4). In addition, this red muscle contains a meshwork of tiny blood vessels which transfer heat back towards the body core. Retaining body heat enables the shark to remain active and react quickly even in cold water (3) (4), and also results in much faster digestion, enabling it to feed again rapidly, should the opportunity arise (3). Thresher sharks are ovoviviparous, meaning that the young develop inside a weakly formed shell within the female. The gestation period is reported to be nine months, with litters of two to seven pups born during the spring (2). Thresher sharks reach maturity at between three and eight years old, and are estimated to live for 45 to 50 years (2).
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Description

With their enormous, curving upper lobe of the tail fin, which can be as long as the body, thresher sharks are one of the most instantly recognisable of all sharks (2). This slender, whip-like tail can be a deadly weapon, used to herd, stun and kill the thresher shark's prey (3). The body is blue-grey to dark grey or blackish on top, with silvery or coppery sides and white undersides (2). The pectoral fins are curved and taper to a point, and the snout is short and pointed (2). The eyes and jaws are relatively small (2), but the thresher shark's sharp teeth are efficient at capturing slippery prey (3). This thresher shark can be distinguished from other threshers by the position of the first dorsal fin which has its leading edge situated above the trailing edge of the pectoral fins (3).
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Comprehensive Description

Description

  Common names: thresher (English), tiburón zorro (Espanol)
 
Alopias vulpinus (Bonnaterre, 1788)


Thintail thresher


Body stout, cylindrical; head short, rounded between eyes; forehead profile convex; no groove on nape; snout short, conical; eyes small, mouth small, ventral; teeth sharply triangular; gill openings - 5, short, last 2 over pectoral base; first dorsal large, ~ midway between pectorals and pelvics; second dorsal and anal very small; pectorals, very long, narrow, curved, with pointed tip; pelvics large; tail not lunate, upper lobe extremely long, ~ equal to body length, fin very thin, small lobe at tip of long lobe about 2x length of 2nd  dorsal fin base; no keels on tail base.

Back and under snout  brown, grey, blue or blackish; belly abruptly white, this color extending onto flank above pectoral fin; pectoral fin tip with white dot.



Size: > 600 cm.

Habitat: oceanic, pelagic.

Depth: 0-550 m.

Circumtropical; Canada to Chile and throughout our region.
   
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Biology

Coastal over continental and insular shelves and epipelagic far from land (Ref. 30573, 43278, 58302). Oceanic although most abundant near land, pelagic at 1-366 m (Ref. 58302). Young often close inshore and in shallow bays (Ref. 5578). Feeds on schooling fishes (including mackerels, bluefishes, clupeids, needlefishes, lancetfishes and lanternfishes), squid, octopi, pelagic crustaceans, and rarely seabirds (Ref. 247). Ovoviviparous, embryos feeding on yolk sac and other ova produced by the mother (Ref. 43278, 50449). Uses its long caudal fin to bunch up and stun prey (Ref. 2850). Spatial and depth segregation by sex in northwestern Indian Ocean populations (Ref. 247). A few attacks on boats are doubtfully attributed to this species, but it is otherwise apparently harmless to humans, though the size of adults of this species command respect (Ref. 247). May cause damage to fishing gear (Ref. 6885). Valued for its meat, liver, hide, and fins; utilized fresh, dried-salted, smoked, and frozen (Ref. 9987).
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Distribution

National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Newfoundland to Cuba
  • North-West Atlantic Ocean species (NWARMS)
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Range Description

This oceanic and coastal shark is virtually circumglobal in tropical to cold-temperate seas, but is most common in temperate waters (Compagno 2001).

Western Atlantic: ranges from Canada (from Bay of Chaleur, Gulf of St. Lawrence, south), USA (whole Atlantic Coast, although it is rare south of New England and in the Gulf of Mexico), Cuba, Mexico, Venezuela, south to Argentina (Bigelow and Schroeder 1948, Russell 1993, Anonymous 1997, Compagno 2001).

Eastern Atlantic: ranges from Norway and the UK, south, including the Mediterranean and Black Seas, Madeira, the Azores, and down the coast of western Africa (Ghana, Côte d?Ivoire) to Angola, Namibia, and South Africa (Moreno et al. 1989, Compagno 2001).

Indian Ocean: South Africa, Tanzania, Somalia, Kenya, northwestern coast of Madagascar, Maldives, Chagos Archipelago, Gulf of Aden, northwest Red Sea, Pakistan, India, Sri Lanka, Sumatra, Australia (Western and South Australia) (Gubanov 1972, Last and Stevens 1994, Compagno 2001). Presence off Oman is unconfirmed.

Western Pacific: southern Japan, Korea, China, Taiwan (Province of China), Australia (Queensland, New South Wales, Victoria, Tasmania, South Australia), New Zealand and several of the Pacific Islands, including, New Caledonia, Society Islands, Fanning Islands (Kiribati) (Last and Stevens 1994, Compagno 2001).

Eastern Pacific: From British Columbia south, along the western coast of the USA (Washington, Oregon, California), Mexico, south to Panama, and from Colombia to southern Chile (Compagno 2001). Also reported off the Hawaiian Islands (Compagno 2001).

Nursery areas (inshore temperate waters appear to be preferred) have been identified in the Adriatic Sea (Notabartolo Di Sciara and Bianchi 1998, Constantini 1997), northeastern Atlantic, western Mediterranean (Alboran Sea), southern California, South Africa and probably elsewhere, with young sharks occurring in shallow bays (Moreno et al. 1989, Compagno 2001, S.E. Smith pers. comm.).
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Zoogeography

See Map (including site records) of Distribution in the Tropical Eastern Pacific 
 
Global Endemism: All species, TEP non-endemic, Circumtropical ( Indian + Pacific + Atlantic Oceans), "Transpacific" (East + Central &/or West Pacific), All Pacific (West + Central + East), East Pacific + Atlantic (East +/or West), Transisthmian (East Pacific + Atlantic of Central America), East Pacific + all Atlantic (East+West)

Regional Endemism: All species, Eastern Pacific non-endemic, Tropical Eastern Pacific (TEP) non-endemic, Continent + Island (s), Continent, Island (s)

Residency: Resident

Climate Zone: North Temperate (Californian Province &/or Northern Gulf of California), Northern Subtropical (Cortez Province + Sinaloan Gap), Northern Tropical (Mexican Province to Nicaragua + Revillagigedos), Equatorial (Costa Rica to Ecuador + Galapagos, Clipperton, Cocos, Malpelo), South Temperate (Peruvian Province )
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Circumglobal in tropical through temperate seas (including Mediterranean Sea, Black Sea, western Baltic Sea, North Sea, Mascarenes, Hawaiian Islands).
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Cosmopolitan in temperate and tropical seas (Ref. 6871). Western Atlantic: Newfoundland, Canada to Cuba, Gulf of Mexico, Venezuela, Brazil to Argentina. Eastern Atlantic: Norway and British Isles to the Mediterranean, Morocco, Ghana and Côte d'Ivoire; also Cape Province, South Africa. Indo-Pacific: scattered localities from the Gulf of Aden and East Africa to the Hawaiian, Society and Fanning islands. Eastern Pacific: Canada to Chile. Population considered reduced (R) in the US Atlantic waters; lower risk/conservation dependent (LR/CD) in US Pacific waters; data deficient (DD) in the rest of Atlantic and rest of Pacific (Ref. 12451). Highly migratory species, Annex I of the 1982 Convention on the Law of the Sea (Ref. 26139).
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Temperate and subtropical seas. From southern Ireland and the North Sea to Madeira and the Mediterranean, Cape of Good Hope; from Nova Scotia and the Gulf of St. Lawrence to Cuba and the northern part of the Gulf of Mexico. Also southern Brazil and northern Argentina. Pacific; from Oregon to Panama and Chile.
  • Bigelow, H. B. and Schroeder, W. C., 1953; Compagno, L. J. V., 1984; Sommer, C., W. Schneider and J.-M. Poutiers, 1996.
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Depth

Depth Range (m): 0 (S) - 550 (S)
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Range

Occurs in oceanic and coastal areas in tropical to cold-temperate seas around the world, but it most common in temperate waters (2).
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Geographic Range

Common thresher sharks, Alopias pelagicus, are found in tropical and temperate temperate waters in almost every major ocean. They are found along the coast of North America from Oregon to Mexico in the Pacific Ocean and from Maine to Florida in the Atlantic Ocean. Common thresher sharks are also commonly found around Asia and occasionally in the central and western Pacific Ocean. Although little is known about the migration of this species, fishing records suggest that they move north, away from the equator, during summer months and that they move south, toward the equator, during winter months.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); atlantic ocean ; pacific ocean (Native )

Other Geographic Terms: cosmopolitan

  • Cartamil, D. 2009. Movement patterns, habitat preferences, and fisheries biology of the common thresher shark (Alopias vulpinus) in the Southern California Bight. San Diego: University of California. Accessed September 16, 2010 at http://www.escholarship.org/uc/item/3908d6cv.
  • Springer, S. 1943. A second species of thresher shark from Florida. Copeia, 1943: 54-55.
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Physical Description

Morphology

Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Size

Length max (cm): 600.0 (S)
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Physical Description

Common thresher sharks weigh 348 kg on average and can reach up to 500 kg. They range from 1.6 to 6 m in length, averaging 2.74 m. Up to 50 % of a thresher's length is due to the characteristic enlarged upper lobe of its caudal fin. Alopias pelagicus is the largest of the thresher species, and, unlike other threshers, they have "erect and narrow cusps" (Springer, 1943) on their teeth. Like other species of threshers, common threshers have relatively small eyes near the front of the head. Common thresher shaks can be identified by their dark green dorsal fin; in other similar species, dorsal fins are blue to purple.

Range mass: 500 (high) kg.

Average mass: 348 kg.

Range length: 1.6 to 6 m.

Average length: 2.74 m.

Other Physical Features: endothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

  • Bernal, D., C. Sepulveda. 2005. Evidence for temperature elevation in the aerobic swimming musculature of the common thresher shark, Alopias vulpinus. Copeia, 2005: 146-151.
  • Eitner, B. 1995. Systematics of the genus Alopias (Lamniformes: Alopiidae) with evidence for the existence of an unrecognized species. Copeia, 1995: 562-571.
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Size

Maximum size: 7600 mm TL
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Max. size

760 cm TL (male/unsexed; (Ref. 6885)); 549 cm TL (female); max. published weight: 348.0 kg (Ref. 40637); max. reported age: 25 years (Ref. 81241)
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to 760 cm TL, max. weight 300 kg.
  • Bigelow, H. B. and Schroeder, W. C., 1953; Compagno, L. J. V., 1984; Sommer, C., W. Schneider and J.-M. Poutiers, 1996.
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Diagnostic Description

Description

Possibly to 609 cm. Also in coastal waters. Eats schooling fish, including mackerels, bluefishes, clupeids, needlefishes, lancetfishes and lanternfishes, also squids, octopi and other pelagic crustaceans, and rarely seabirds. Spatial and depth segregation by sex in northwestern Indian Ocean populations. Uses its long caudal fin to bunch up and even stun schooling prey (Ref. 2850). Unconfirmed boat attacks. Valued for its meat, liver, hide and fins; utilized fresh, dried-salted, smoked and frozen (Ref. 9987).
  • Anon. (1996). FishBase 96 [CD-ROM]. ICLARM: Los Baños, Philippines. 1 cd-rom pp.
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A large thresher with relatively small eyes, curved, narrow-tipped pectoral fins, a narrow-tipped caudal fin, and a conspicuous white patch over the pectoral fin bases (Ref. 5578). Second dorsal origin well behind the rear tip of the pelvic fin (Ref. 559). Upper lobe of caudal fin very long and strap-like, about as long as or longer than length of rest of shark; lower lobe short but well developed (Ref. 13570). Brown, grey, blue-grey, or blackish on back and underside of snout, lighter on sides and abruptly white below; a white area extends from the abdomen over the pectoral-fin bases; pectoral-, pelvic-, and dorsal fins blackish, white dots sometimes present on pectoral-, pelvic-, and caudal- fin tips (Ref. 13570).
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Ecology

Habitat

Habitat Type: Marine

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nektonic
  • North-West Atlantic Ocean species (NWARMS)
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warm and temperate areas of all the World's oceans
  • North-West Atlantic Ocean species (NWARMS)
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Habitat and Ecology

Habitat and Ecology
The Common Thresher Shark is virtually circumglobal in temperate oceans, penetrates into tropical waters (Compagno 1984), and also has a noted tolerance for cold waters (Castro 1983, Moreno et al.1989). While found both in coastal and oceanic waters, it is most abundant in waters up to 40 or 50 miles offshore (Strasburg 1958, Gubanov 1972, Moreno et al. 1989, Bedford 1992). It ranges between surface waters and 366 m depth (Compagno 1984).

Maximum recorded size varies with sex and geographic location and ranges from 415-573 cm total length (TL) (Gubanov 1972, Cailliet et al. 1983, Compagno 1984, Moreno et al. 1989). Size at maturity varies. Females are reported to mature from 260-465 cm total length (Strasburg 1958, Cailliet et al. 1983, Bedford 1983, Bigelow and Schroeder 1948, Gubanov 1978, Ebert 2003) and males at 260-426.7 cm TL (Cailliet and Bedford 1983, Cailliet et al. 1983). Estimated age at maturity for females ranges from 3-9 years (Bigelow and Schroeder 1948, Strasburg 1958, Gubanov 1978, Cailliet et al. 1983, Cailliet and Bedford 1983, Hanan 1984) and from 3-7 years for males (Cailliet et al. 1983, Cailliet and Bedford 1983). The species reaches an age of at least 24 years (Gervelis 2005) and Cailliet et al. (1983) stated that off California it may reach an age of 50 years; providing k coefficients from the von Bertalanffy growth equation ranging from 0.158-0.215. These parameters were early estimates based on a sample size of 143 specimens (16 male, 23 female, 104 unknown). The most recent estimates of generation time are 8-14 years (Cortés 2008 unpubl. data).

Alopias vulpinus is viviparous, with oophagy and a gestation period of nine months (Gubanov 1978, Moreno et al. 1989, Bedford 1992, Gilmore 1993, Cailliet et al. 1983). Litter sizes range from only two in the Indian Ocean to between 3-7 in the Northeast Atlantic, while 3-4 (predominantly four) pups are common in the eastern Pacific (Gubanov 1972, Gubanov 1978, Holts 1988, Cailliet and Bedford 1983, Hanan 1984, Moreno et al. 1989). Size at birth is 100-158 cm TL (Cailliet et al. 1983, Hanan 1984). Ratios of male to female pups also vary geographically. Moreno et al. (1989) noted a high degree of sexual and size segregation in the northeast Atlantic during pupping season. Mating occurs in middle to late summer and parturition occurs during the spring in both the Northeast Atlantic and the eastern Pacific (Moreno et al. 1989, Bedford 1992). In the Indian Ocean, there is a high degree of sexual segregation, between January and May, with pregnant females in the western Indian Ocean and males around the Maldives (Gubanov 1972). However, pregnant females have also been noted in August and November indicating that birth of young thresher sharks in this area occurs throughout the year (Gubanov 1978). Size at parturition varies considerably, from 115 cm and 156 cm TL with slight variation among geographical locations (Compagno 1984, Moreno et al. 1989). Young A. vulpinus, in all locations, generally remain close to shore after parturition and during their first few years (Moreno et al. 1989).

The range of prey items taken varies geographically, however their diet consists mostly of small bait fish. Prey items include anchovies (Engraulis and Anchoa), herring (Clupeidae), mackerel (Scomber), Pacific hake (Merluccius), lancetfish (Alepisaurus), lanternfishes (Myctophhidae), Pacific salmon (Oncorynchus), squids, octopus, pelagic crabs and shrimp (Gubanov 1972, Stick and Hreha 1989, Bedford 1992, Goldman pers. obsv.).

Systems
  • Marine
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Depth: 0 - 550m.
Recorded at 550 meters.

Habitat: pelagic.
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Environment

pelagic-oceanic; oceanodromous (Ref. 51243); marine; depth range 0 - 550 m (Ref. 26346), usually 0 - 200 m (Ref. 55168)
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Depth range based on 78 specimens in 1 taxon.
Water temperature and chemistry ranges based on 62 samples.

Environmental ranges
  Depth range (m): 0 - 2700
  Temperature range (°C): 3.160 - 24.665
  Nitrate (umol/L): 0.317 - 31.978
  Salinity (PPS): 32.507 - 36.095
  Oxygen (ml/l): 2.420 - 6.494
  Phosphate (umol/l): 0.106 - 1.900
  Silicate (umol/l): 1.138 - 34.276

Graphical representation

Depth range (m): 0 - 2700

Temperature range (°C): 3.160 - 24.665

Nitrate (umol/L): 0.317 - 31.978

Salinity (PPS): 32.507 - 36.095

Oxygen (ml/l): 2.420 - 6.494

Phosphate (umol/l): 0.106 - 1.900

Silicate (umol/l): 1.138 - 34.276
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Pelagic; depth range 0-550 m. Coastal over continental and insular shelves and epipelagic far from land. Young often found close inshore and in shallows bays.
  • Bigelow, H. B. and Schroeder, W. C., 1953; Compagno, L. J. V., 1984; Sommer, C., W. Schneider and J.-M. Poutiers, 1996.
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Salinity: Marine, Marine Only

Inshore/Offshore: Offshore Only, Offshore

Water Column Position: Surface, Near Surface, Mid Water, Water column only

Habitat: Water column

FishBase Habitat: Pelagic
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The thresher shark inhabits both coastal waters and oceans far from land, from the surface to depths of at least 366 metres (2). Young thresher sharks are often found close inshore and in shallow bays (2).
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Common thresher sharks primarily live in temperate waters beyond the continental shelf and do not stray much more than 30 km from the coast. During the day, they stay near the edge of the continental shelf at an average depth of 110 m. Common thresher sharks have been documented diving to depths of 217 m below sea level, though this is uncommon. At night, members of this species spend most of their time at a mid-range depths, remaining near or on the continental shelf.

Range depth: 217 (high) m.

Average depth: 110 m.

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: pelagic ; coastal

  • The International Commission for the Conservation of Atlantic Tunas. Preliminary investigations into the age and growth of the shortfin mako, Isurus oxyrinchus, white shark, Carcharodon carcharias, and thresher shark, Alopias vulpinus, in the western North Atlantic Ocean. 54. Madrid, Spain: The International Commission for the Conservation of Atlantic Tunas. 2002.
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Trophic Strategy

Occurs on the continental shelf and slope (Ref. 75154).
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Feeds on schooling fishes, squid, octopi, pelagic crustaceans, and rarely seabirds.
  • Bigelow, H. B. and Schroeder, W. C., 1953; Compagno, L. J. V., 1984; Sommer, C., W. Schneider and J.-M. Poutiers, 1996.
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Feeding

Feeding Group: Carnivore

Diet: octopus/squid/cuttlefish, Pelagic crustacea, bony fishes, sea snakes/mammals/turtles/birds
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Food Habits

Like most sharks, common thresher sharks are carnivores and feed mainly on small fish that travel in schools. Thresher sharks use their enlarged caudal fin as a means to herd schools of fish into tightly packed balls to maximize strike success. Common threshers eat a variety of fish, including sardines, and different species of anchovies, mackerel, hake, squid and red crab from deep waters. In warmer waters, members of this species feed primarily on anchovies, but in cooler waters they feed mostly on squid and sardines.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore )

  • California Cooperative Oceanic Fisheries Investigations. Diet differences in the thresher shark (Alopias vulpinus) during transition from a warm-water regime to a cool-water regime off California-Oregon, 1998–2000. 45. Silver Spring, MD: National Marine Fisheries Service. 2004.
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Associations

Ecosystem Roles

Common thresher sharks are often used as bio-indicators of pollutants due to their diet and near-shore habitat. Common threshers act as host for many parasitic copepods such as Nemesis robusta and Bariaka alopiae. Nemesis robusta usually infects the gills of common thresher sharks causing gill erosion and inflammation, resulting in reduced gas exchange. Another common copepod parasite of this speices is Gangliopus pyriformis, although exactly how this copepod affects common threshers is unknown. Like most sharks and rays, common threshers have a mutualistic relationship with pilot fish. Pilot fish eat copepods and other parasites from the shark while the shark provides for the pilot fish.

Mutualist Species:

Commensal/Parasitic Species:

  • Baughman, J., S. Springer. 1950. Biological and economic notes on the sharks of the Gulf of Mexico, with special reference to those of Texas, and with a key for their indentification. American Midland Naturalist, 44: 96-152.
  • Benz, G., S. Adamson. 1990. Disease caused by Nemesis robusta (van Beneden, 1851) (Eudactylinidae: Siphonostomatoida: Copepoda) infections on gill filaments of thresher sharks (Alopias vulpinus (Bonnaterre, 1758)), with notes on parasite ecology and life history. Canadian Journal of Zoology, 68/6: 1180-1186.
  • Borucinska, J., K. Kotran, M. Shackett, T. Barker. 2009. Melanomacrophages in three species of free-ranging sharks from the northwestern Atlantic, the blue shark Prionacae glauca (L.), the shortfin mako, Isurus oxyrhinchus Rafinesque, and the thresher, Alopias vulpinus (Bonnaterre). Journal of Fish Diseases, 32: 883-891.
  • Izawa, K. 2010. Free-living stages of the parasitic copepod, Gangliopus pyriformis gerstaecker, 1854 (Siphonostomatoida, Pandaridae) reared from eggs. Crustaceana, 83: 829-837.
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Predation

There are few known predators of common thresher sharks. Other sharks, like makos, reef sharks and even members of the same species, eat juvenile common threshers. Pups usually keep to shallow nursery areas that are separate from adults as a defense from predation.

Known Predators:

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Life History and Behavior

Behavior

Diet

Bluefish, menhaden, shad, mackerel and other schooling fishes, as well as squid
  • North-West Atlantic Ocean species (NWARMS)
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Communication and Perception

As solitary animals, very little is known about communication between common thresher sharks. Because this species has poor vision, they often rely on other senses to detect prey. Like most sharks, common threshers perceive their environment in many ways. The lateral line in all sharks detects vibrations in the surrounding waters. This aides in locating prey from great distances, as vibrations travel well in water. Common threshers also have a strong sense of smell, and chemicals can be detected in low concentrations. Upon finding a potential meal, most threshers will bump the object with their nose or take a small test bite to determine if the object is edible before committing to a full strike. Common thresher sharks also use electromagnetic senses to perceive their environment and hunt prey. They use sensory organs clustered in their nose and head to sense impulses in the water from injured and dying fish.

Communication Channels: visual ; electric

Perception Channels: visual ; tactile ; chemical ; electric ; magnetic

  • California Cooperative Oceanic Fisheries Investigations. Feeding habits of the common thresher shark (Alopias vulpinus) sampled from the California-based drift gill net fishery, 1998-1 999. 42. Silver Spring, MD: National Marine Fisheries Service. 2001.
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Life Cycle

Ovoviviparous, embryos feed solely on the ova produced by the mother after the yolk sac is absorbed (oophagy) (Ref. 50449), 2 to 4 young in a litter (usually 2) (Ref. 247). Size at birth 114-150 cm (Ref. 247). Distinct pairing with embrace (Ref. 205).
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Development

Common thresher sharks are oviparous. Immediately after birth, young are independent and albe to survive on their own. However, because newborn sharks are 69 to 92 cm in length, they are easy targets for larger sharks. Consequently, thresher sharks stay in a nursery area for roughly 3 years until they are large enough to avoid predation. This species grows fairly slowly, taking 9 to 13 years to reach sexual maturity. Males usually mature earlier than females, at around 9 to 10 years age, while females mature at 12 to 13 years. Common thresher sharks are indeterminate growers.

Development - Life Cycle: indeterminate growth

  • National Oceanic and Atmosphere Administration. Age and growth estimates of the bigeye thresher shark, Alopias superciliosus, in Northeastern Taiwan waters. 96. Seattle, Wa: National Marine Fisheries Service. 1998.
  • Bodson, L. 1983. Aristotle's statement on the reproduction of sharks. Journal of the History of Biology, 16: 391-407.
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Life Expectancy

Lifespan/Longevity

The lifespan of common thresher sharks in the wild is poorly documented, and threshers are not held in captivity. Other species of thresher sharks, such as Alopias superciliosus and Alopias pelagicus, can live 20 to 30 years in the wild. The largest common thresher shark ever recorded was 4.75 m long and 510 kg. Using the growth coefficient of common thresher sharks, this shark was determined to be 43 years old. Thus Alopias pelagicus may have a greater lifespan than other members of its genus.

Range lifespan

Status: wild:
43 (high) years.

Average lifespan

Status: wild:
25 years.

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Reproduction

In American waters it is probable that threshers are born throughout their range. Small specimens have been caught off New England to Florida. The embryos do not develop a placental attachment with the mother. Two or four embryos have been reported in gravid females.
  • Bigelow, H. B. and Schroeder, W. C., 1953; Compagno, L. J. V., 1984; Sommer, C., W. Schneider and J.-M. Poutiers, 1996.
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Egg Type: Live birth, No pelagic larva
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In some parts of the world, common thresher sharks breed all year long. The migratory patterns of common thresher sharks near North America suggest they breed in northern waters during the spring and sumer and release their pups into nurseries along the coast as they travel south for the winter months. Common thresher sharks are polygynous (the male impregnates multiple females), but little is known about their mating behavior.

Mating System: polygynous

In some parts of the world, common thresher sharks are thought to breed all year long. The migratory patterns of common thresher sharks near North America suggest they breed in northern waters during the spring and sumer and release their pups into nurseries along the coast as they travel south for the winter months. Females are oviviparous and can only carry two pups at a time. Pups are born independent, but remain in a nursery area for approximately 3 years for safety. Male common thresher sharks reach maturity at 9 to 10 years of age, and females at 12.3 to 13.4 years of age.

Breeding season: year-round

Range number of offspring: 1 to 2.

Range time to independence: 0 to 5 minutes.

Range age at sexual or reproductive maturity (female): 12.3 to 13.4 years.

Range age at sexual or reproductive maturity (male): 9 to 10 years.

Key Reproductive Features: year-round breeding ; sexual ; fertilization (Internal ); ovoviviparous

There is little to no post-birth parental investment among common thresher sharks. Once born, pups are fully independent and remain in a shallow nursery area for protection.

Parental Investment: no parental involvement

  • National Oceanic and Atmosphere Administration. Age and growth estimates of the bigeye thresher shark, Alopias superciliosus, in Northeastern Taiwan waters. 96. Seattle, Wa: National Marine Fisheries Service. 1998.
  • The International Commission for the Conservation of Atlantic Tunas. Preliminary investigations into the age and growth of the shortfin mako, Isurus oxyrinchus, white shark, Carcharodon carcharias, and thresher shark, Alopias vulpinus, in the western North Atlantic Ocean. 54. Madrid, Spain: The International Commission for the Conservation of Atlantic Tunas. 2002.
  • Bodson, L. 1983. Aristotle's statement on the reproduction of sharks. Journal of the History of Biology, 16: 391-407.
  • Cartamil, D. 2009. Movement patterns, habitat preferences, and fisheries biology of the common thresher shark (Alopias vulpinus) in the Southern California Bight. San Diego: University of California. Accessed September 16, 2010 at http://www.escholarship.org/uc/item/3908d6cv.
  • Fujita, K. 1981. Oviphagous embryos of the pseudocarchariid shark, Pseudocarcharias kamoharai, from the central pacific. Japanese Journal of Ichthyology, 28: 37-44.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Alopias vulpinus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 24 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

CTTTATTTAATCTTTGGTGCATGAGCAGGAATAGTGGGAACAGCCCTC---AGCCTTCTAATTCGAGCCGAGTTAGGCCAGCCCGGATCACTCCTAGGGGAT---GATCAGGTCTATAATGTTATCGTAACCGCCCATGCATTTGTAATAATCTTCTTCATGGTTATACCCGTAATAATTGGGGGATTTGGAAACTGATTAGTACCCTTAATA---ATTGGTGCACCAGACATGGCCTTCCCGCGAATAAATAACATAAGCTTTTGACTCCTTCCCCCTTCTTTTCTCTTACTCCTAGCTTCAGCTGGGGTTGAAGCTGGAGCTGGCACTGGTTGAACAGTTTATCCCCCCTTAGCTGGCAACTTAGCACATGCTGGGGCATCTGTTGACTTG---GCCATTTTCTCGCTTCATTTAGCAGGTATCTCATCAATTTTAGCTTCAATTAACTTTATTACAACTATCATTAATATAAAACCACCAGCCATCTCTCAATATCAAACACCATTATTTGTATGATCAATCCTAGTAACAACCATCCTCCTCCTCTTATCCCTCCCAGTACTCGCAGCC---GGCATCACAATATTATTAACTGATCGAAACCTAAACACAACATTCTTTGACCCAGCAGGAGGAGGAGATCCAATTCTTTACCAACATCTA------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------TTT
-- end --

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Statistics of barcoding coverage: Alopias vulpinus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 27
Specimens with Barcodes: 35
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: NNR - Unranked

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NatureServe Conservation Status

Rounded Global Status Rank: GNR - Not Yet Ranked

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IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A2bd+3bd+4bd

Version
3.1

Year Assessed
2009

Assessor/s
Goldman, K.J., Baum, J., Cailliet, G.M., Cortés, E., Kohin, S., Macías, D., Megalofonou, P., Perez, M., Soldo, A. & Trejo, T.

Reviewer/s
Fowler, S.L., Valenti, S.V. & participants of the Pelagic Shark Red List Workshop (Shark Red List Authority)

Contributor/s

Justification
All members of genus Alopias, the thresher sharks, are listed as Vulnerable globally because of their declining populations. These downward trends are the result of a combination of slow life history characteristics, hence low capacity to recover from moderate levels of exploitation, and high levels of largely unmanaged and unreported mortality in target and bycatch fisheries.

The Common Thresher Shark (Alopias vulpinus) is virtually circumglobal, with a noted tolerance for cold waters. This species is especially vulnerable to fisheries exploitation (target and by-catch) because its epipelagic habitat occurs within the range of many largely unregulated and under-reported gillnet and longline fisheries, in which it is readily caught. It is an important economic species in many areas and is valued highly for its meat and large fins. Its life-history characteristics (2?4 pups per litter; 8?14 year generation period) and high value in both target and bycatch fisheries make it vulnerable to rapid depletion. Serious declines have occurred where this species has been heavily fished, for example in the 1980s eastern central Pacific drift gillnet fishery, where reported landings collapsed to 27% of peak levels between 1982 and the late 1980s. Analyses of pelagic longline CPUE data from logbook reports covering the species? entire range in the northwest and western central Atlantic vary according to the time period, but suggest thresher shark stocks declined by between 63?80% during 1986?2000. There is evidence that thresher sharks are being increasingly targeted by pelagic fisheries for swordfish and tuna (e.g., in the Mediterranean Sea) in attempts to sustain catches, and exploitation is increasing in these areas. The high value of the species and its exploitation by unmanaged fisheries combined with its biological vulnerability, indicate that at least some, if not most, subpopulations in other parts of the world are likely to be equally, or more seriously at risk than those for which data are available and, unlike the Californian stock, are not the subject of management, enabling stocks to rebuild.

In addition to the Vulnerable global assessment, a number of regional assessments have also been designated for this species as follows: Near Threatened in the eastern central Pacific; Vulnerable (VU A2bd) in the northwest Atlantic and western central Atlantic; Vulnerable (VU A3bd) in the Mediterranean Sea; and Data Deficient in the Indo-west Pacific.

Eastern Central Pacific
Reported landings in the drift gillnet fishery for this species that developed off the west coast of the USA in the late 1970s, collapsed from a peak of 1,089.5 t in 1982 to less than 300 t by the late 1980s (decline of ~70%). This fishery was effectively eliminated by restrictions on the use of gill nets by 1990, and the population began to slowly recover to just below 50% of the initial subpopulation size. The Common Thresher Shark is still caught as bycatch or as a secondary target, although to a far lesser extent, of the swordfish gillnet fishery. It is clear that the species depends on adequate management measures, and would otherwise be at risk of overfishing. All this considered, the species is assessed as Near Threatened in this region based on significant population declines, which are now managed in US waters.

Northwest and Western Central Atlantic
Estimates of trends in abundance from standardized catch rate indices of the U.S. pelagic longline fishery suggest that this species has likely undergone a decline in abundance in this region. Thresher sharks are generally recorded by genus by observers as well as in logbooks, which includes both Common Thresher Shark and Bigeye Thresher Shark (A. superciliosus) in this region, of which Common Thresher Shark is the less common. The area covered by the analyses, ranging from the equator to about 50°N, encompasses the confirmed range of threshers in this region. Estimates of the decline based on logbook and observer records of combined thresher sharks from 1986?2005 range between 50?80%. Fishing pressure on thresher sharks began over two decades prior to the start of this time series, thus the estimated declines are not from virgin biomass. Furthermore the sample size in the latter observer analysis was also very small compared with the logbook analyses which both showed declines. Given the apparent decline in abundance in this region and high fishing pressure from pelagic fleets, this species is assessed as Vulnerable A2bd in the northwest and western central Atlantic.

Mediterranean Sea
Adults and juveniles of Common Thresher Shark are regularly caught as bycatch in longline, purse seine and mid-water fisheries throughout the Mediterranean Sea, as well as in recreational fisheries. The species has some important parturition and nursery areas this region, for example the Alboran sea, where aggregations of pregnant females have been observed. Recent investigations show that pelagic sharks, including this species, are being increasingly targeted in the Alboran Sea by the Moroccan swordfish driftnet fleet. Data from this fishery suggest that both annual catches and mean weights of Common Thresher Shark have fallen as a result of fishing mortality. Given that pelagic fishing pressure is high and ongoing throughout the Mediterranean Sea, increased targeting and the decline in catches described above, Common Thresher Shark is currently assessed as Vulnerable (VU A3bd) in this region.

Northeast Atlantic
The Common Thresher Shark is taken as primarily as bycatch of longline fisheries for tuna and swordfish in the Northeast Atlantic, and also in driftnets and gillnets. It is very likely that this catch is retained. Limited information is available on thresher shark catch in this region and estimated landings are still considered incomplete. Prior to 2000, estimated landings fluctuated at 17?13 t, in 2000?2001 they exceeded 100 t, after which they dropped to 4 t in 2002 and have not exceeded 7 t since. Increased targeting of pelagic sharks by Moroccan drift-netters in the Alboran Sea and Strait of Gibraltar mentioned above, has also likely impacted Common Thresher Shark in the northeast and eastern central Atlantic. The species is currently assessed as Near Threatened in this region and there is a need to collect further data on the status the species in this area.

Indo-West Pacific
Little information is currently available on Common Thresher Shark in the Indo-West Pacific. Whereas records of Bigeye Thresher Shark and Pelagic Thresher are recorded in the catches of fisheries operating in this region, albeit very under-reported, very little information is available on catches of Common Thresher Shark. Although pelagic fishing effort in this region is high, with reported increases in recent years, the Common Thresher Shark is more characteristic of cooler waters and further information needs to be collected on records and catches of the species in this region.

History
  • 2002
    Data Deficient
  • 2000
    Data Deficient
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IUCN Red List: Listed, Data deficient

CITES: Not listed
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Status

Classified as Data Deficient (DD) by the IUCN Red List (1).
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Because common thresher sharks are sold in many foreign fish markets, the demand for their meat is high. In many areas of the Atlantic ocean, populations of common thresher sharks have been reduced up to 67 % in the last ten years. However, stricter catch-and-release policies in the Pacific have led to more stable populations. The IUCN lists Alopias pelagicus as threatened. Many conservation attempts have developed "no-fishing" marine reserves to reduce the number of common thresher sharks that are caught in nets. However, forcing commercial fisheries to move fishing zone to establish marine reserves has consequently put other species in danger.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: vulnerable

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Population

Population
Common Thresher Sharks appear to exhibit little to no immigration and emigration between geographic areas. The California drift gill net fishery provided insight into the population dynamics of this species, indicating that numerous isolated subpopulations or stocks exist globally (see Threats section). An ongoing global population genetic study (Trejo 2004) using DNA sequences from the mitochondrial control region indicates significant structuring of A. vulpinus populations within the Pacific Ocean, and significant structure between Pacific and northwest Atlantic populations. Differences in length at maturity and fecundity of specimens examined from different regions of the world also provides evidence for isolated subpopulations or stocks (Gubanov 1972, Moreno et al. 1989, Bedford 1992). In the absence of records of transatlantic migrations a single northeast Atlantic and Mediterranean stock of A. vulpinus is assumed (ICES 2007).

Population Trend
Decreasing
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Threats

Major Threats
Members of the genus Alopias, thresher sharks, are threatened from a combination of slow life history characteristics, hence low capacity to recover from moderate levels of exploitation, and high levels of largely unmanaged and unreported mortality in target (for fins and their valuable meat) and bycatch fisheries.

Many countries fish thresher sharks commercially throughout their extensive ranges, with A. vulpinus probably being the most important species (Compagno 1990). This species is frequently caught by offshore longline and pelagic gillnet fisheries (Maguire et al. 2006), is also fished with anchored bottom and surface gillnets, and is a bycatch of other gear including bottom trawls and fish traps (Maguire et al. 2006). Although sometimes referred to as a bycatch in fisheries for other pelagic fishes, this bycatch is normally utilised and would better be described as a secondary target catch. They are also an important sport fishery resource, the meat is considered excellent for consumption, and the large fins highly valued. The growing and largely unregulated shark fin trade also represents a serious threat to thresher sharks. Clarke et al. (2006) report that thresher sharks compose at least 2?6% of the trade in a market study using DNA-based species identification techniques.

The impact of fisheries on A. vulpinus on a global scale, while difficult to assess, has most likely been significant. For example, Japanese and Russian vessels fish the northwest Indian Ocean and central Pacific, and Mexican-Japanese joint ventures have operated longline vessels off Baja California, Mexico, for many years. Furthermore, the number of pelagic sharks landed by fishing fleets in all oceans has become increasingly important in recent years (Mejuto et al. 2006). However, catch statistics are not available (Compagno 2001, Holts 1988, Smith 1998) and where they are, they are under-reported. A recent FAO review of the status of highly migratory pelagic species states: ?unless demonstrated otherwise, it is prudent to consider Alopias species as being fully exploited or overexploited globally? (Maguire et al. 2006).

Eastern Central Pacific
A target pelagic gillnet fishery for this species developed off the west coast of the USA, Eastern Central Pacific (particularly California, and also Washington and Oregon) in the late 1970s (Goldman 2005, Maguire et al. 2006). This fishery serves as a well documented case of population depletion and provides strong evidence that there are numerous isolated subpopulations or stocks globally. Starting with 15 vessels in 1977, the fishery expanded to over 225 vessels in 1982 (Holts 1988, Hanan et al. 1993). The fishery peaked in 1982 with reported landings of 1,089.5 t (Anonymous 1993), declining due to overfishing to less than 300 t by the late 1980s (Maguire et al. 2006). Fishing had heavily reduced the number of juvenile and subadult A. vulpinus off central and southern California, virtually eliminating them from the catch. In 1996, California catches of Common Thresher Shark were down to one-fifth of former levels (Smith 1998). This fishery was effectively eliminated by restrictions on the use of gill nets by 1990 (Bedford 1992, Smith 1998, Maguire et al. 2006). It was originally believed that a Pacific-wide distribution of the species would act as a buffer against over-harvesting (Bedford 1992, Smith 1998). However, this was shown not to be the case, as that portion of the population remained at low levels for several years, and is only reappeared in the catch records and in market places some time later (Bedford 1992, Smith 1998). The species is still caught as bycatch or as a secondary target, although to a far lesser extent, of the swordfish gillnet fishery and may be sold for higher prices in the market than swordfish (Bedford 1992, Smith 1998, Maguire et al. 2006).

While the majority of fishery data for this species in the Pacific has come from California, it is fished in numerous locations throughout its range there. The Spanish pelagic longline fishery for swordfish and sharks is expanding rapidly in the Pacific, with effort expanding from the traditional grounds in the southeast Pacific into the central south Pacific and areas of the north Pacific in recent years (Mejuto 2005). A. vulpinus is taken in both artisanal and commercial longline fisheries in areas off South America, including Peru and Chile (M. Romero pers. comm., Bonfil et al. 2005). Hong Kong customs data shows that Peru is amongst the 20 countries that export the most dried fins to Hong Kong (Bonfil et al. 2005).

Indo-West Pacific
Little information is currently available on A. vulpinus in the Indo-West Pacific. Whereas records of A. superciliosus and A. pelagicus are recorded in the catches of fisheries operating in this region, albeit very under-reported, very little information is available on catches of A. vulpinus. Although pelagic fishing effort in this region is high, with reported increases in recent years, A. vulpinus is more characteristic of cooler waters and further information needs to be collected on records and catches of the species in this region.

Northwest and Western Central Atlantic
Thresher sharks are also an important pelagic species in the north Atlantic, although A. vulpinus is only sporadically recorded in the northwest and western central Atlantic and A. superciliosus is the more common thresher shark in this area. Thresher sharks are generally recorded by genus by observers as well as in logbooks. Analysis of U.S. Atlantic pelagic longline data from their scientific observer program for 1992?2005, suggest that the region of the US east coast where A. vulpinus is somewhat common is from about 35°N?40°N (approximately North Carolina to Philadelphia), where A. vulpinus: A. superciliosus are caught in a ratio of ~1:3 (Baum unpublished data). The first longline fisheries in the Atlantic were begun by the Japanese in 1956 in the western equatorial waters (Uozumi and Nakano 1996). The fleet expanded rapidly in the 1960s, and covered almost the entire Atlantic by the late 1960s (Bonfil 1994), including the areas currently fished by the American fleet. Fishing pressure is high and ongoing and as A. vulpinus is an incidental catch in these fisheries monitoring of catches of this species is extremely limited. Currently, there are no management measures specific to this species in any EEZ or within international waters, and no stock assessments have been done. In Canada and the U.S., less than 5% of the pelagic longlining fleets are monitored by observers, making it difficult to elucidate reliable trends in abundance from these data. Fisheries monitoring in international waters is even more limited. The pelagic longline fishing grounds for the US fleet extend from the Grand Banks (about 45°N) in the northwest Atlantic to 5?10°S off the South American coast, within which geographical areas of longline fishing are defined for classification (Cortés et al. 2007).

Baum et al. (2003) concluded from their analysis of Northwest Atlantic pelagic longline data that the relative abundance of all thresher sharks (A. vulpinus and A. superciliosus combined) had declined 80% from 1986?2000. This analysis is based on estimates of trends in abundance from standardized catch rate indices of the U.S. pelagic longline fishery logbook data, and the fifteen year time period is over one generation length for this species. Although the analysis is not species specific, the sample size of thresher sharks in this data is over 20,000. Furthermore, the area covered by the dataset analysed, ranging from the equator to about 50°N, encompasses the confirmed range of A. vulpinus in these two regions (Compagno 2001). An alternative analysis of the same logbook dataset for 1986-2005 that also combined A. vulpinus and A. superciliosus, resulted in an overall decline of 63% (Cortés et al. 2007). Fishing pressure on thresher sharks began over two decades prior to the start of this time series, thus the estimated declines are not from virgin biomass.

A more recent analysis of Alopias species trends from scientific observer data between 1992 and 2005 in the same U.S. pelagic longline fishery found an almost identical instantaneous rate of decline (-0.12 up to the year 2000) as in the logbook analysis (Baum et al. unpublished manuscript). For this nine year period (1992?2000), the decline amounts to 68%, therefore the decline back to when the fishery started in the 1960s (less than three generation period of 51 years) would be much greater. However, because of recent increases in the catch rates in 2004 and 2005, the overall trend from 1992-2005 of -0.024 was non-significant, and would amount to only a 26% decline (Baum et al. unpublished manuscript). Cortés et al. (2007) also conducted an alternative analysis of this same observer dataset for the same time period that also combined A. vulpinus and A. superciliosus. This analysis of the observer dataset showed a trend opposite to that of the logbook analysis, with a 28% increase since 1992. In contrast, the nominal observer series showed a 39% decline and the logbook index for the same time period showed a decrease of 50%. Furthermore the sample size in the observer analysis was much smaller (n=14?84) than that in the logbook analysis (n=112?1,292) and thus the trend estimated should be regarded with caution. Cortés et al.'s (2007) observer analysis was restricted to four out of the 11 geographical areas covered by the pelagic longline fishing fleet to keep a balanced statistical design (Cortés et al. 2007). Their full logbook analysis, which showed an overall decline of 63%, had much larger sample sizes and is thus better to estimate trends with more certainty (Cortés et al. 2007).

Southwest Atlantic
The thresher shark A. vulpinus is not as common in regional longline catches compared as the bigeye thresher A. superciliosus. Amorim et al. (1998) document its occurrence in the Santos (São Paulo) tuna longline fishery as ?low? with only six specimens observed from 1974 to 1996. Gadig et al. (2001) reported on small numbers of juveniles taken by gillnet off São Paulo State.

Mediterranean Sea
Adults and juveniles of Alopias vulpinus are regularly caught as bycatch in longline, purse seine and mid-water fisheries throughout the Mediterranean Sea, as well as in recreational fisheries (Lipej et al. 2004). This species has some important parturition and nursery areas in the Mediterranean (Adriatic and Alboran Seas). Moreno and Moron (1992) observed aggregations of pregnant females of A. vulpinus in the Strait of Gibraltar.

Even though driftnetting is banned in Mediterranean waters, this practise has continued illegally (WWF 2005). The Moroccan swordfish driftnet fleet in the Alboran Sea operates year round, resulting in high annual effort levels (Tudela et al. 2005). Even though sharks are a secondary target or bycatch of this fishery, some boats deploy driftnets 1?2 miles from the coast where the chance of capturing pelagic sharks is higher. The catch rate for A. vulpinus is higher in boats actively fishing for sharks (from 0.7 to 1.5 N/fishing operation and 0.09 to 0.11 catch per km net). Both annual catches and mean weights of Alopias vulpinus have fallen as a result of fishing mortality in the Moroccan driftnet fishery, illustrating the likely impact of this illegal fishery on stocks in the Alboran Sea and adjacent Atlantic (Tudela et al. 2005). Valeiras et al. (2003) also report that pelagic sharks are forming an increasing proportion of the catch of Spanish swordfish sleets. Pelagic fishing pressure is high and ongoing throughout the Mediterranean Sea (Tudela 2004, Megalofonou et al. 2000).

Northeast Atlantic
A. vulpinus is caught primarily as a bycatch of longline fisheries for tuna and swordfish in the northeast Atlantic, and are also taken in driftnets and gillnets (ICES 2005, 2007). As a highly valuable species, it is very likely that this bycatch is retained (ICES 2005). Limited information is available on thresher shark catch in this region. ICES 2006 reports estimated landings of thresher shark at 13?107 t from 1996 to 2005 in the ICES area, however these data are still considered incomplete. Prior to 2000, estimated landings fluctuated at 17?13 t, in 2000?2001 they exceeded 100 t, after which they dropped to 4 t in 2002 and have not exceeded 7 t since. Increased targeting of pelagic sharks by Moroccan drift-netters in the Alboran Sea and Strait of Gibraltar (Tudela et al. 2005), mentioned above, has also likely impacted A. vulpinus in this area.
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Vulnerable (VU) (A2bd+3bd+4bd)
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The thresher shark is an important economic species in many areas (1), such as the northwestern Indian Ocean, the western, central and eastern Pacific, and the North Atlantic (2). Its flesh is highly prized for human consumption, its fins are sought after for shark fin soup, its skin can be used for leather and the liver provides vitamin rich oil (2). The tendency of the thresher shark to fight strongly when caught also makes it a popular target for sports anglers (2). The World Conservation Union (IUCN) considers there to be insufficient data on the thresher shark to determine the extent to which it may be threatened by these activities, although there is evidence that this shark is highly vulnerable to over-fishing (1). In California, a fishery started in 1977 for several species of shark, including the thresher. Catches peaked in 1982 and declined thereafter, showing that uncontrolled fishing can rapidly deplete a population. This fishery was outlawed in 1990 (5). Declines have also been observed in the Northwest Atlantic, where thresher shark numbers are estimated to have declined by over 75 percent between 1986 and 2000 (6). Here, and in many other areas, fishing of the thresher shark continues, often without any management measures in place (1).
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Management

Conservation Actions

Conservation Actions
Time and area restrictions were imposed off California, USA, since 1990, but A. vulpinus is not managed internationally and there are no quotas.

Family Alopiidae is listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea, which urges States to cooperate over the management of these species. No such management yet exists. Precautionary adaptive collaborative management of target and bycatch fisheries is urgently needed for this biologically vulnerable shark. It is also essential to improve data collection and develop stock assessments for this species. Listing on international resource management agreements, such as the Convention on Migratory Species (CMS) could help to drive improvements in national and regional management and facilitate collaboration between states, for this species and other migratory sharks.

The adoption of shark finning bans by fishing states (e.g., USA, Australia), regional entities (EU) and regional fisheries organisations (e.g., ICCAT, IATTC, WCPFC) is accelerating and should increasingly prevent the fishing of thresher sharks for their fins alone.
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Conservation

The thresher shark is believed to be able recover from the impact of fisheries fairly quickly (2) (5); for example, since fishing of the thresher shark was banned in California in 1990 this population has begun to recover (5) (7). However, the brevity of the Californian fishery shows how uncontrolled fishing can decrease a population very quickly, indicating that harvesting of this species should be carried out with caution and with adequate management measures in place (1) (5). Unfortunately, unmanaged fisheries operating throughout the world might be over-exploiting the thresher shark, and reducing numbers to a level they may not always be able to recover from.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial; gamefish: yes
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Economic Importance for Humans: Negative

Because common thresher sharks stay beyond areas where humans swim, they do not pose any physical threat to humans. They do, however, cause damage to commercial fisheries by destroying nets and other equipment when caught in drift nets.

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Economic Importance for Humans: Positive

Common thresher sharks are an integral part of global commercial fishing. Although they are not target speecies for fishing in the Americas, they are often incidentally caught in commercial gill nets. In other countries, including China, they are the third most targeted catch of fisheries, valued less only to the game fish Xiphias gladius and sailfish Istiophorus albicans. Common thresher sharks make up a large part of Chinese fish markets. In many areas, the demand for thresher shark meat has led to overfishing and a major decrease in population size. Also, the livers of common thresher sharks contain a small amount of oil that is considered valuable and sold in high dollar amounts.

Positive Impacts: food ; body parts are source of valuable material

  • Baum, J., R. Myers, D. Kehler, B. Worm, S. Harley, P. Doherty. 2003. Collapse and conservation of shark populations in the Northwest Atlantic. Science, 299: 389-392.
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Wikipedia

Common thresher

The common thresher (Alopias vulpinus) is the largest species of thresher shark, family Alopiidae, reaching some 6 m (20 ft) in length. About half of its length consists of the elongated upper lobe of its caudal fin. With a streamlined body, short pointed snout, and modestly sized eyes, the common thresher resembles (and has often been confused with) the pelagic thresher (A. pelagicus). It can be distinguished from the latter species by the white of its belly extending in a band over the bases of its pectoral fins. The common thresher is distributed worldwide in tropical and temperate waters, though it prefers cooler temperatures. It can be found both close to shore and in the open ocean, from the surface to a depth of 550 m (1,800 ft). It is seasonally migratory and spends summers at lower latitudes.

The long tail of the common thresher, the source of many fanciful tales through history, is used in a whip-like fashion to deliver incapacitating blows to its prey. This species feeds mainly on small schooling forage fishes such as herrings and anchovies. It is a fast, strong swimmer that has been known to leap clear of the water, and possesses physiological adaptations that allow it to maintain an internal body temperature warmer than that of the surrounding sea water. The common thresher has an aplacental viviparous mode of reproduction, with oophagous embryos that feed on on undeveloped eggs ovulated by their mother. Females typically give birth to four pups at a time, following a gestation period of nine months.

Despite its size, the common thresher is minimally dangerous to humans due to its relatively small teeth and timid disposition. It is highly valued by commercial fishers for its meat, fins, hide, and liver oil; large numbers are taken by longline and gillnet fisheries throughout its range. This shark is also esteemed by recreational anglers for the exceptional fight it offers on hook-and-line. The common thresher has a low rate of reproduction and cannot withstand heavy fishing pressure for long, a case in point being the rapid collapse of the thresher shark fishery off California in the 1980s. With commercial exploitation increasing in many parts of the world, the International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable.

Taxonomy and phylogeny[edit]

Early illustration of a common thresher from Natural History of Victoria (1881).

The first scientific description of the common thresher, as Squalus vulpinus, was written by French naturalist Pierre Joseph Bonnaterre in the 1788 Tableau encyclopédique et méthodique des trois règnes de la nature.[3] In 1810, Constantine Samuel Rafinesque described Alopias macrourus from a thresher shark caught off Sicily. Later authors recognized the genus Alopias as valid while synonymizing A. macrourus with S. vulpinus, and thus the common thresher's scientific name became Alopias vulpinus.[2]

The specific epithet vulpinus is derived from the Latin vulpes meaning "fox", and in some older literature the species name was given incorrectly as Alopias vulpes.[4] "Fox shark" is the earliest known English name for this species and is rooted in classical antiquity, from a belief that it was especially cunning. In the mid-19th century, the name "fox" was mostly superseded by "thresher", referencing the shark's flail-like use of its tail. This species is often known simply as thresher shark or thresher; Henry Bigelow and William Schroeder introduced the name "common thresher" in 1945 to differentiate it from the bigeye thresher (A. superciliosus).[5] It is also known by many other common names, including Atlantic thresher, grayfish, green thresher, long-tailed shark, sea ape, sea fox, slasher, swiveltail, thintail thresher, thrasher shark, and whiptail shark.[2][6]

Morphological and allozyme analyses have agreed that the common thresher is basal to the clade formed by the bigeye thresher and the pelagic thresher (A. pelagicus).[2][4] The closest relative of this species within the family may be a fourth, unrecognized thresher shark species off Baja California, reported from allozyme evidence by Blaise Eitner in 1995.[7] However, the existence of this fourth species has yet to be confirmed by other sources.[1][2]

Description[edit]

The common thresher can be distinguished from other thresher sharks by the appearance of its head and the coloration above its pectoral fins.

The common thresher is a fairly robust shark with a torpedo-shaped trunk and a short, broad head. The dorsal profile of the head curves evenly down to the pointed, conical snout. The eyes are moderately large and lack nictitating membranes. The small mouth is arched and, unlike in other thresher sharks, has furrows at the corners. There are 32-53 upper and 25-50 lower tooth rows; the teeth are small, triangular, and smooth-edged, lacking lateral cusplets. The five pairs of gill slits are short, with the fourth and fifth pairs located over the pectoral fin bases.[2][4]

The long, falcate (sickle-shaped) pectoral fins taper to narrowly pointed tips. The first dorsal fin is tall and positioned slightly closer to the pectoral fins than the pelvic fins. The pelvic fins are almost as large as the first dorsal fin and bear long, thin claspers in males. The second dorsal and anal fins are tiny, with the former positioned ahead of the latter. There are crescent-shaped notches on the caudal peduncle at the upper and lower origins of the caudal fin. The upper caudal fin lobe is enormously elongated as is characteristic of threshers, measuring about as long as the rest of the shark; the thin, gently curving lobe is held at a steep upward angle and has a notch in the trailing margin near the tip.[2][5]

The skin is covered by small, overlapping dermal denticles, each with three horizontal ridges and three to five marginal teeth. This species is metallic purplish brown to gray above, becoming more bluish on the flanks. The underside is white, which extends over the pectoral and pelvic fin bases; this pattern is in contrast to the pelagic thresher, which is solidly colored over these fins. The meeting line between the dorsal and ventral coloration is often irregular. There may be a white spot at the tips of the pectoral fins.[2][5] The common thresher is the largest thresher shark species, commonly reaching 5 m (16 ft) long and 230 kg (510 lb) in weight.[8] The confirmed length record for this shark is 5.7 m (19 ft), while the maximum possible length may be 6.1–6.5 m (20–21 ft).[2] The heaviest individual on record is a 4.8 m (16 ft) female that weighed 510 kg (1,120 lb).[9]

Distribution[edit]

The range of the common thresher encompasses tropical and cold-temperate waters worldwide. In the western Atlantic, it is found from Newfoundland to the Gulf of Mexico, though it is rare south of New England, and from Venezuela to Argentina. In the eastern Atlantic, it has been reported from the North Sea and the British Isles to Ghana (including Madeira, the Azores, and the Mediterranean and Black Seas), as well as from Angola to South Africa. In the Indo-Pacific, this species is known from Tanzania to India and the Maldives, Japan and Korea to southeastern China, Sumatra, eastern Australia, and New Zealand; it also occurs around a number of Pacific islands including New Caledonia, the Society Islands, Tabuaeran, and Hawaiian Islands. In the western Pacific, it has been recorded from British Columbia to Chile, including the Gulf of California.[1][2]

The common thresher is migratory, moving to higher latitudes following warm water masses. In the eastern Pacific, males travel further than females, reaching as far as Vancouver Island in the late summer and early fall. Juveniles tend to remain in warm nursery areas.[4] There appear to be separate populations with different life history characteristics in the eastern Pacific and western Indian Ocean and possibly elsewhere; this species is not known to make transoceanic movements.[10] In the northwestern Indian Ocean, males and females segregate by location and depth during the pupping season from January to May.[8] Analysis of mitochondrial DNA has revealed substantial regional genetic variation within common threshers in all three oceans. This could support the idea that, despite being high mobile, sharks from different areas rarely interbreed.[11]

Habitat[edit]

Common threshers are inhabitants of both continental waters and the open ocean. They tend to be most abundant in proximity to land, particularly the juveniles which frequent near-coastal habitats such as bays.[2] Most individuals are encountered near the surface, but this species has been recorded to at least a depth of 550 m (1,800 ft).[12]

Biology and ecology[edit]

Common threshers are active, strong swimmers; there are infrequent reports of them leaping completely out of the water.[13] Like the fast-swimming sharks of the family Lamnidae, the common thresher has a strip of aerobic red muscle along its flank that is able to contract powerfully and efficiently for long periods of time.[14] In addition, they have slow-oxidative muscles centrally located within their bodies and a blood vessel countercurrent exchange system called the rete mirabile ("wonderful net"), allowing them to generate and retain body heat. The temperature inside the red muscles of a common thresher averages 2°C (3.6°F) above that of the ambient seawater, though there is significant individual variation.[15] Unlike the pelagic and bigeye threshers, the common thresher lacks an orbital rete mirabile to protect its eyes and brain from temperature changes.[16]

Immature common threshers fall prey to larger sharks. Aside from observations of killer whales feeding on common threshers off New Zealand,[17] adults have no known natural predators. Parasites documented from the common thresher include the protozoan Giardia intestinalis,[18] the trematodes Campula oblonga (not usual host)[19] and Paronatrema vaginicola,[20] the tapeworms Acanthobothrium coronatum,[21] Anthobothrium laciniatum,[22] Crossobothrium angustum,[23] Hepatoxylon trichiuri, Molicola uncinatus,[24] Paraorygmatobothrium exiguum,[25] P. filiforme,[26] and Sphyriocephalus tergetinus,[27] and the copepods Dinemoura discrepans, Echthrogaleus denticulatus,[28] Gangliopus pyriformis,[29] Kroeyerina benzorum,[30] Nemesis aggregatus, N. robusta, N. tiburo,[31] Nesippus orientalis,[32] and Pandarus smithii.[28]

Feeding[edit]

The common thresher is often hooked by the tail, because it uses its long caudal fin to attack prey.

The long upper tail fin lobe of the common thresher is used to strike and incapacitate prey.]] Some 97% of the common thresher's diet is composed of bony fishes, mostly small schooling forage fish such as mackerel, bluefish, herring, needlefish, and lanternfish. Before striking, the sharks compact schools of prey by swimming around them and splashing the water with its tail, often in pairs or small groups. Threshers are also known to take large, solitary fishes such as lancetfish, as well as squid and other pelagic invertebrates.[12] Off California, common threshers feed mostly on the northern anchovy (Engraulis mordax), with Pacific hake (Merluccius productus), Pacific sardine (Sardinops sagax), Pacific mackerel (Scomber japonicus), market squid (Loligo opalescens), and pelagic red crab (Pleuroncodes planipes) also being important food items. The sharks concentrate on a few prey species during cold water years, but become less discriminating during less productive, warmer El Niño periods.[33]

There are numerous accounts of common threshers using the long upper lobes of their tail fins to stun prey, and they are often snagged on longlines by their tails after presumably striking at the bait. In July 1914, shark-watcher Russell J. Coles reported seeing a thresher shark use its tail to flip prey fish into its mouth, and that one fish that missed was thrown a "considerable distance". On April 14, 1923, noted oceanographer W.E. Allen observed a 2 m (6.6 ft) thresher shark pursuing a California smelt (Atherinopsis californiensis) off a pier at the Scripps Institution of Oceanography. The shark overtook the small fish and swung its tail above the water like a "coachwhip" with "confusing speed", severely injuring its target. In the winter of 1865, Irish ichthyologist Harry Blake-Knox claimed to have seen a thresher shark in Dublin Bay use its tail to strike a wounded loon (probably a great northern diver, Gavia immer), which it then swallowed. Blake-Knox's account was subsequently disputed by other authorities, who asserted that the thresher's tail is not rigid or muscular enough to effect such a blow.[8]

Life history[edit]

Embryos of the common thresher are nourished by eggs during development.

Like other mackerel sharks, common threshers are aplacental viviparous. They give birth to litters of two to four (rarely six) pups in the eastern Pacific, and three to seven pups in the eastern Atlantic.[10] They are believed to reproduce throughout their range; one known nursery area is the Southern California Bight. Breeding occurs in the summer, usually July or August, and parturition occurs from March to June following a gestation period of nine months. The developing embryos are oophagous, feeding on eggs ovulated by the mother.[4] The teeth of small embryos are peg-like and non-functional, being covered by a sheath of soft tissues. As the embryos mature, their series of teeth become progressively more like those of adults in shape, though they remain depressed and hidden until shortly before birth.[34]

Newborn pups usually measure 114–160 cm (3.74–5.25 ft) long and weigh 5–6 kg (11–13 lb), depending on the size of the mother. The juveniles grow about 50 cm (1.6 ft) a year while adults grow about 10 cm (0.33 ft) a year.[12] The size at maturation appears to vary between populations. In the eastern North Pacific males mature at 3.3 m (11 ft) and five years old, and females at around 2.6–4.5 m (8.5–14.8 ft) and seven years old. They are known to live to at least 15 years of age and their maximum lifespan has been estimated to be 45–50 years.[4][10]

Human interactions[edit]

While any large shark is capable of inflicting injury and thus merits respect, the common thresher poses little danger to humans. Most divers report that they are shy and difficult to approach underwater. The International Shark Attack File lists a single provoked attack by the thresher shark and four attacks on boats, which were probably incidental from individuals fighting capture. There is an unsubstantiated report of a common thresher acting aggressively towards a spearfisherman off New Zealand.[8]

Famed big-game angler Frank Mundus, in his book Sportsfishing for Sharks, recounted a tale in which a longline fisherman off the Carolinas leaned over the side of his boat to examine something large that he had hooked, and was decapitated by the caudal fin of a thresher shark estimated to be 5 m (16 ft) long. The head supposedly fell into the water and was never recovered. This account is considered highly improbable by most authors.[8]

Commercial fishing[edit]

A common thresher hooked on a longline; this shark is taken commercially by many countries.

The common thresher is widely caught by offshore longline and pelagic gillnet fisheries, especially in the northwestern Indian Ocean, the western, central, and eastern Pacific, and the North Atlantic. Participating countries include the former USSR, Japan, Taiwan, Spain, the United States, Brazil, Uruguay, and Mexico. The meat is highly prized for human consumption cooked, dried and salted, or smoked. In addition, their skin is made into leather, their liver oil is processed for vitamins, and their fins are used for shark fin soup. The United Nations Food and Agricultural Organization (FAO) reported a worldwide common thresher take of 411 metric tons in 2006.[10]

In the United States, a drift gillnet fishery for the common thresher developed in southern California in 1977, beginning with 10 vessels experimenting with a larger-sized mesh. Within two years the fleet had increased to 40 vessels, and the fishery peaked in 1982 when 228 vessels landed 1,091 metric tons. The common thresher population rapidly collapsed from overfishing, with landings decreasing to less than 300 metric tons a year by the late 1980s and larger size classes disappearing from the population.[10][35] Common threshers are still taken commercially in the United States, with about 85% coming from the Pacific and 15% from the Atlantic. The largest catches remain from the California-Oregon gillnet fishery, which had shifted its focus to the more valuable swordfish (Xiphius gladius) but still take threshers as bycatch. Small numbers of Pacific threshers are also taken by harpoons, small-mesh driftnets, and longlines. In the Atlantic, threshers are primarily taken on longlines meant for swordfish and tuna.[36][37]

Recreational fishing[edit]

Common threshers are well regarded by sports fishers as one of the strongest fighting sharks alongside the shortfin mako shark (Isurus oxyrhinchus), and are ranked as game fish by the International Game Fish Association (IGFA). They are pursued by anglers using rod and reel off California, South Africa, and elsewhere. Frank Mundus has called thresher sharks "exceedingly stubborn" and "pound for pound, a harder fish to whip" than the mako.[8] Fishing for the common thresher is similar to that for the mako; the recommended equipment is a 24 kg (53 lb) rod and a big-game reel holding at least 365 m (400 yd) of 24 kg (53 lb) line. The ideal method is trolling with baitfish, either deep or allowing it to drift.[38][39]

Conservation[edit]

NOAA researchers tagging a common thresher; such efforts are critical for developing conservation measures.

All three thresher shark species were reassessed from Data Deficient to Vulnerable by the International Union for Conservation of Nature (IUCN) in 2007.[1] The rapid collapse of the Californian subpopulation (over 50% within three generations) prompted concerns regarding the species' susceptibility to overfishing in other areas, where fishery data is seldom reported and aspects of life history and population structure are little-known.[40] In addition to continued fishing pressure, common threshers are also taken as bycatch in other gear such as bottom trawls and fish traps, and are considered a nuisance by mackerel fishers as they become entangled in the nets.[12][10]

The United States manages common thresher fisheries via regulations such as commercial quotas and trip limits, and recreational minimum sizes and retention limits. Shark finning is illegal under U.S. federal law. The Atlantic common thresher fishery is regulated by the National Marine Fisheries Service (NMFS) Highly Migratory Species Management Division through the 2006 Consolidated Atlantic Highly Migratory Species (HMS) Fishery Management Plan (FMP), and the Pacific common thresher fishery is regulated by the Pacific Fishery Management Council through the Fishery Management Plan (FMP) for U.S. West Coast Fisheries for Highly Migratory Species (HMS).[36][37] In the 1990s, after the depletion of common thresher stocks by the California gillnet fishery, the fleet was limited to 70 boats and restrictions were placed on season, operation range, and landings. There is evidence that the California subpopulation is recovering, and the potential population growth rate has been estimated to be 4–7% per year.[35]

Historical perceptions[edit]

The Greek philosopher Aristotle (384–322 BCE) wrote some of the earliest observations about the common thresher. In his Historia Animalia, he claimed that hooked threshers had a propensity for freeing themselves by biting through fishing lines, and that they protected their young by swallowing them. These "clever" behaviors, which have not been borne out by science, led the ancient Greeks to call it alopex (meaning "fox"), on which its modern scientific name is based.[8]

An oft-repeated myth about the common thresher is that they cooperate with swordfish to attack whales. In one version of events, the thresher shark circles the whale and distracts it by beating the sea to a froth with its tail, thereby allowing the swordfish to impale it in a vulnerable spot with its rostrum. In an alternate account, the swordfish positions itself beneath the whale, while the thresher leaps out of the water and lands on top of the whale, hammering it onto the swordfish's rostrum. Yet other authors describe the thresher "cutting huge gashes" in the side of the whale with its tail. Neither threshers nor swordfish however are known to feed on whales or indeed possess the dentition to do so. The story may have arisen from mariners mistaking the tall dorsal fins of killer whales, which do attack large cetaceans, for thresher shark tails. Swordfish bills have also been found embedded in blue and fin whales (likely accidents due to the fast-moving fish's inertia), and thresher sharks do exhibit some of the aforementioned behaviors independent of whales.[8][41]

References[edit]

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