Why Have Thresher Sharks Got Such Long Tails?

An article this week in the Plos One journal documents how pelagic thresher sharks (Alopias pelagicus) utilise that wonderfully long caudal fin of theirs. Threshers are a relatively rare species and not that much is known about their habitats and hunting techniques.

The research team studied them off the coast of Pescador Island in the Philippines which is one of the few places the sharks come into the shallows making them easier to ogle. They visit shallower water to allow the local species of wrasse to clean them of the parasites they’ve picked up in the depths. Despite thresher sharks not being very keen on divers, they still show up and begrudgingly stick around, so the cleaning process is obviously pretty important to them.

The team found that these lithe foxes of the deep use their exceedingly long tail to whip schools of prey. This tail-whipping is so violent that the recipients are stunned or sometimes killed outright. This is a clear advantage for the shark, meaning that each attack gains them multiple fishies rather than having to catch small snacks, one at a time.

It’s also seems that the tail whip is so powerful that it breaks the hydrogen and oxygen bonded together in water to cause the small bubbles seen in the flurry. Anyone who’s tried to give their little brother a dead leg in the swimming pool will know how difficult it is to get up any speed underwater, so that’s a pretty darned impressive feat. The tip of their tail can hit speeds of nearly 40 meters per second, which is about 90 mph.

Here’s an American man talking over some video footage of the thresher shark threshing for his sushi.