A shark can rest on the seabed

Some sharks settle on the seabed. Even while they lie still, they can pump water over their gills. The gills take oxygen from the water.

A motionless shark. Posture alone cannot establish sleep.
The way a shark is lying tells only part of the story. Scientists need other clues to tell if it is asleep. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

How can you tell if it is asleep?

Scientists look at how a shark reacts when something disturbs it. A shark that’s asleep may be harder to get a reaction from than one that’s awake.

How can we recognise sleep? Researchers compare responsiveness, posture and oxygen uptake.
Researchers compare responsiveness, posture and oxygen uptake. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

How water passes over the gills

Some sharks use their mouths to pump water over their gills. For others, water flows in through the mouth and over the gills as they swim.

Breathing while still. Some sharks pump water using movements of the mouth and throat.
Some sharks move water over their gills even when they are not swimming. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

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