Many people know that marine mammals, like whales, porpoises and dolphins, breathe air, like wedo.

But, many people don't know that marine mammals have developed some interesting sleepinghabits in order to accommodate their regular trips up to the surface for air.

Today, A Moment ofScience looks at what its like to sleep with the fishes.

Unlike our own breathing, which does not require conscious effort, marine mammals mustconsciously go to the surface of the water to breathe through a blowhole on top of their heads.

Because of this, marine mammals don't sleep for a solid 8 hours a night, the way we do.

Some marine mammals sleep while swimming.

Whales nap for brief periods while swimmingalongside an alert friend who guides them.

In fact, young whales must sleep alongside their motherbecause the mother's slipstream actually pulls the calf along: it will sink if the mother stops.

Other marine mammals, like dolphins, sleep while floating on the surface of the water or take shortcatnaps while floating below the surface.

Researchers claim that while marine mammals sleep theirbrain is always partially alert.

Aside from these brief naps, dolphins are active most of the night.

Of course, marine mammals are equipped to handle underwater sleeping.

They haveproportionately larger lungs, exchange air more fully at each breath, and carry more oxygen intheir blood than we do, so they can hold their breath long enough to sleep with the fishes.