Thresher shark

Alopias vulpinus (Common Thresher)
Thresher sharks are instantly recognizable by their extraordinarily long upper caudal (tail) fin—often as long as or longer than the body. Their bodies are streamlined, with moderate size heads, relatively small dorsal fins, and a greyish or brownish coloration on top with a lighter underside. Teeth are small, smooth, blade-like, and arranged in rows.
Thresher sharks often hunt schooling fish (e.g. mackerel, tuna, herring) using their long tail as a whip to stun prey. Many species are solitary, though pairing or small group hunting is sometimes observed. Reproduction is ovoviviparous: embryos develop inside the mother; litters are small (commonly 2–4 pups). Growth is slow; maturity may take many years.

Where divers may encounter it
Commonly seen in offshore pelagic diving grounds, seamounts, drop-offs, or in deeper open water. Juveniles sometimes approach nearer to coasts or over continental shelves.

Diving tips
Expect brief encounters—the sharks are fast, mobile, and generally shy. Use wide-angle lenses. Stay calm, avoid chasing. Sunlit, clear water helps for sightings. Diving with experienced operators in known thresher habitats (e.g. Pacific islands) offers the best chance.

All thresher shark species are generally listed as Vulnerable by the IUCN, due to low reproductive rates and heavy fishing pressures. The population trend is decreasing globally.

Did you know?

The long tail of a thresher shark is used like a whip; their hunting strategy includes stunning or herding prey by slashing in tight arcs. Also, one documented birth of a thresher shark was caught on camera — a rare event in marine biology.

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