Thresher sharksAlopiidae

It hunts with its tail, and it swings it forward over its own head.

The upper lobe of a thresher's tail is as long as the entire rest of the animal, which reads as decoration until you watch it work. The shark drives into a school of small fish, brakes hard with its pectoral fins, pitches the front of its body down and throws the tail overhead like an axe. The tip moves fast enough that the water cannot close in behind it: the strike leaves a trail of collapsing bubbles, and fish that were never touched are stunned or killed outright by the pressure wave. Several drop at once. The shark turns around and picks them up at leisure.

This was suspected for a long time before anybody saw it. The evidence was indirect and slightly comic: threshers kept coming up on longlines hooked through the tail, which is hard to explain unless the animal had struck the bait with it. Underwater video off the 🇵🇭 Philippines finally caught the full sequence in 2013, and what stood out was how deliberate it is, aimed and finished inside a fraction of a second, with the shark braking first so the tail has something to swing against.

Everything else about the family is quiet by comparison. Litters are tiny, usually two pups, each born well over a meter long, and the embryos spend the pregnancy eating a supply of unfertilized eggs the mother keeps producing for them.

One thresher is on the 🌊 Red Sea list, the pelagic thresher, and it is not an animal anyone here plans a dive around. It lives offshore and deep, comes up along the outer reefs around first light, sometimes to be worked over by cleaner fish, and is gone within seconds of noticing you. It is listed as endangered, largely through being caught by fleets that were not aiming at it.