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.

The common thresher has an aplacental viviparous mode of reproduction, with oophagous embryos that feed on undeveloped eggs ovulated by their mother.

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.

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.

[14] Separate populations with different life history characteristics apparently exist in the eastern Pacific and western Indian Ocean and possibly elsewhere; this species is not known to make transoceanic movements.

[20] 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.

The temperature inside the red muscles of a common thresher averages 2 °C (3.6 °F) above that of the ambient seawater, though significant individual variation is seen.

Parasites documented from the common thresher include the protozoan Giardia intestinalis,[25] the trematodes Campula oblonga (not usual host)[26] and Paronatrema vaginicola,[27] the tapeworms Acanthobothrium coronatum,[28] Anthobothrium laciniatum,[29] Crossobothrium angustum,[30] Hepatoxylon trichiuri, Molicola uncinatus,[31] Paraorygmatobothrium exiguum,[32] P. filiforme,[33] and Sphyriocephalus tergetinus,[34] and the copepods Dinemoura discrepans, Echthrogaleus denticulatus,[35] Gangliopus pyriformis,[36] Kroeyerina benzorum,[37] Nemesis aggregatus, N. robusta, N. tiburo,[38] Nesippus orientalis,[39] and Pandarus smithii.

[40] Before striking, the sharks compact schools of prey by swimming around them and splashing the water with their tails, often in pairs or small groups.

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.

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.

[42] 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.

[6][15] While any large shark is capable of inflicting injury and thus merits respect, the common thresher poses little danger to humans.

[citation needed] 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 United Nations Food and Agriculture Organization reported a worldwide common thresher take of 411 metric tons in 2006.

[15] 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.

The largest catches remain from the California-Oregon gillnet fishery, which had shifted its focus to the more valuable swordfish (Xiphias gladius), but still takes threshers as bycatch.

[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 are seldom reported and aspects of life history and population structure are little known.

[44][45] 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.

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.

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.

The story may have arisen from mariners mistaking the tall dorsal fins of killer whales, which do attack large cetaceans, for thresher shark tails.