Observations of bottlenose dolphins in aquariums and zoos, and of whales and dolphins

whales and dolphins

Cetacea is an infraorder that comprises the 94 species of whales, dolphins, and porpoises. It is divided into toothed whales (Odontoceti) and baleen whales (Mysticeti), which diverged from each other some time in the Eocene 26 to 17 million years ago (mya).

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in the wild, show two basic methods of sleeping: they either rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal.

How do whale breathe when they sleep?

So whales can sleep literally with one eye open. (plus one brain hemisphere 'awake') to remember to breathe. Or if able to, they can hold there breaths for such long times that they can sleep between breaths.

How long do whales usually sleep?

They cannot sleep for much longer than 30 minutes without risking lowering their body temperature due to inactivity. A very common assumption is that whales sleep with half of their brain 'shut off' and one eye closed.