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TRESHER SHARK

All 3 thresher shark species are now listed as VULNERABLE by the International Union for the Conservation of Nature and Natural Resources (IUCN press release 2007).

VULNERABILITY

Thresher sharks are among the more demanded shark species for global fisheries.  They are prized for their high quality meat which is used fresh, frozen, smoked and dried-salted.  Their fins are prized for shark-fin soup, their livers for vitamin extraction and their hides are used in the production of leather goods.  Alopias pelagicusrepresents 12% of Taiwan’s shark catch with an average 3,100 units (222 MT) taken per annum.  Methods employed in the hunt for thresher  shark species are dominated by commercial and recreational long-line fishing practices.  Their low fecundity  of 2 pups per litter over long gestation periods classifies them as a K-species (Liu et al. 1999).  This factor combined with their relative proclivity for habitat subjected to high intensity oceanic fisheries, raises concern over the viability of population sustainability.  In 2002, Baum et al. reported that 80% of global thresher shark populations have been lost to fishing pressure over the past 15 years.  The results of this study showed that if unified conservation efforts are not applied, thresher sharks are likely to be eradicated from many of their chosen habitats.

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Thresher sharks inhabit warm and temperate waters worldwide. They prefer cool pelagic waters but will wander into coastal areas as well in pursuit of fish.

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PEW MAP.

Bigeye thresher: • Endangered in north-western, western, and central Atlantic • Near Threatened in south-western Atlantic

Common thresher: • Near Threatened in the easterncentral Pacific • Vulnerable wherever else it is found

Pelagic thresher: • Vulnerable wherever it is found

 

Juvenile threshers are often found close inshore and in shallow bays.

FEEDING BEHAVIOR

Threshers feed on squid, octopuses, crustaceans and small schooling fish such as bluefish, needlefish, lancetfish, lanternfish, menhaden, shad, mackerel, and others. They are also thought to stun prey with blows from their powerful tails.

 

83% In the eastern-central Pacific, thresher populations have declined in abundance by 83 percent.20

 

Conclusion Although shark populations are in decline, it is not too late to reverse that trend. Increased international collaboration and protections can help these populations rebound. Sharks have been an essential part of the marine ecosystem for more than 400 million years. Protecting their populations will take a true global commitment. If governments can come together to conserve sharks, and organizations such as CITES and CMS, along with regional fisheries management organizations, can function effectively, such efforts will leave a lasting legacy of healthy populations of these iconic species. That will help ensure abundant, productive marine ecosystems and oceans

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IUCN Red List status The bigeye thresher (Alopias superciliosus), common thresher (A. vulpinus), and pelagic thresher (A. pelagicus) are listed as Vulnerable globally on the IUCN Red List. Regionally, the bigeye thresher is Endangered in the northwestern, western, and central Atlantic, and Near Threatened in the south-western Atlantic. The common thresher is Near Threatened in the eastern-central Pacific, with the pelagic thresher assessed as Vulnerable wherever it is found.