Sharks freeze when you turn them upside down — and scientists have found no good reason why...

[Michie]

Imagine watching your favorite nature documentary. The predator lunges rapidly from its hiding place, jaws wide open, and the prey … suddenly goes limp. It looks dead.

For some animals, this freeze response—called "tonic immobility"—can be a lifesaver. Possums famously "play dead" to avoid predators. So do rabbits, lizards, snakes, and even some insects.

But what happens when a shark does it?

In our recent study, we explored this strange behavior in sharks, rays and their relatives. In this group, tonic immobility is triggered when the animal is turned upside down—it stops moving, its muscles relax, and it enters a trance-like state. Some scientists even use tonic immobility as a technique to safely handle certain shark species.

But why does it happen? And does it actually help these marine predators survive?

The mystery of the 'frozen shark'​

Continued below.

Sharks freeze when you turn them upside down—and there's no good reason why

Imagine watching your favorite nature documentary. The predator lunges rapidly from its hiding place, jaws wide open, and the prey … suddenly goes limp. It looks dead.

phys.org

 

[chevyontheriver]

Imagine watching your favorite nature documentary. The predator lunges rapidly from its hiding place, jaws wide open, and the prey … suddenly goes limp. It looks dead.

For some animals, this freeze response—called "tonic immobility"—can be a lifesaver. Possums famously "play dead" to avoid predators. So do rabbits, lizards, snakes, and even some insects.

But what happens when a shark does it?

In our recent study, we explored this strange behavior in sharks, rays and their relatives. In this group, tonic immobility is triggered when the animal is turned upside down—it stops moving, its muscles relax, and it enters a trance-like state. Some scientists even use tonic immobility as a technique to safely handle certain shark species.

But why does it happen? And does it actually help these marine predators survive?

The mystery of the 'frozen shark'​

Continued below.

Sharks freeze when you turn them upside down—and there's no good reason why

Imagine watching your favorite nature documentary. The predator lunges rapidly from its hiding place, jaws wide open, and the prey … suddenly goes limp. It looks dead.

phys.org

Interesting. I had never heard of that before. Back in my salad years I swam in a shark pen filled with young Hammerheads about three feet long.

Still in my salad years I banded birds with the St. Paul Science Museum. Once you take the birds out of the mist net they flew into they are put in cloth sacks for a short time. You then grab them with their neck between your first two fingers with them on their backs in your palm. Put the numbered metal band on a leg, gently crimp it, and then the fun starts. You open up your hand with the bird still on it's back. And it just lays there. You can blow on it's tummy. Sometimes that does the job and they fly off. Or just turn your hand over and the bird flies off. Otherwise they can lay there for a long time. But do not try this with a Blue Jay. It doesn't seem to work on them. They will just try to peck you and struggle and most likely draw blood from your hand or arm.