Fish
Common Thresher Shark
Alopias vulpinus · also called common thresher shark, thresher shark, fox shark
The common thresher shark carries a weapon behind it: an upper tail lobe as long as the rest of its body. It is not a decoration or just a rudder — the shark whips it overhead like a bullwhip, fast enough to boil the water, to stun whole schools of fish at a stroke.
Overview
Common thresher sharks live in temperate and tropical seas worldwide, from the surface to about 550 metres, often near the coast but also far offshore. They hunt schooling fish — anchovies, sardines, herring, mackerel — and squid. They are partly warm-blooded, keeping their swimming muscles and eyes above water temperature, which sharpens their speed and vision, as in makos and great whites.
Hunting with the tail
Underwater footage confirmed what fishers had long claimed: the thresher hits fish with its tail. Charging a bait ball, it brakes with its pectoral fins, throws its body forward, and flicks the long upper tail lobe up and over its head in a whip-crack that stuns or kills several fish at once. The shark then loops back and collects the disabled prey. Very few fish use a body part as a striking weapon like this.
Not a threat to people
Threshers are shy and equipped for small prey; there are no confirmed fatal unprovoked attacks. The only real danger is the tail of a hooked shark, which can strike hard.
Reproduction
Females mature at about 5 years and carry only 2–4 pups for around nine months. The embryos hatch from eggs inside the mother and eat unfertilised eggs (oophagy) before birth.
Status
The common thresher is Vulnerable and declining. Slow reproduction plus targeted fishing (meat, fins, oil) and heavy longline and gillnet bycatch — its long tail entangles easily — have cut global populations. All three thresher species are on CITES Appendix II, and it also breaches dramatically, probably to shed parasites.
Common Thresher Shark: common questions
How does a thresher shark use its tail to hunt?
The upper lobe of a thresher's tail fin is enormously elongated, roughly the same length as the shark's head and body combined. Underwater video has shown that the shark does not just herd fish with it — it actively strikes. Swimming into or alongside a bait ball, the thresher brakes with its pectoral fins and throws its whole body forward, flicking the long tail up and over its head like a bullwhip at speeds that create cavitation bubbles. The impact and shockwave stun or kill several fish at once, and the shark then turns and calmly picks up the disabled prey. It is one of very few fish known to use a body part as a hunting weapon in this way.
Is the thresher shark dangerous to people?
Essentially not. Threshers are shy of divers and are built to catch small schooling fish, not large prey. There are only a handful of recorded thresher-shark incidents involving humans, most of them bites on fishing lines or on fishers handling a hooked shark, and no confirmed fatal unprovoked attacks. The one real hazard is the tail itself — a large thrashing thresher on a line or brought alongside a boat can deliver a powerful blow with that whip-like fin.
Why is the thresher shark threatened?
It has the classic vulnerabilities of a large shark — slow growth, late maturity, and only two to four pups per litter — combined with heavy fishing pressure. Threshers are caught deliberately for their meat, fins, skin, and liver oil, and they are taken in large numbers as bycatch on tuna and swordfish longlines and in gillnets, where their long tail makes them especially prone to entanglement. Because they often bite at a baited hook with the tail, they are also frequently foul-hooked. Global populations have declined enough for the species to be listed as Vulnerable, and all three thresher species are on CITES Appendix II.
Do thresher sharks really jump out of the water?
Yes. Common threshers are strong breachers and will launch their whole bodies clear of the surface, sometimes spinning. The usual explanation is parasite removal — the leap and the slap of re-entry help knock off skin parasites and hitch-hiking remoras — and it may also play a role in hunting or communication. Their partly warm-blooded muscles give them the burst power for it. Anglers who hook threshers frequently see spectacular jumps during the fight.