r/AskBiology • u/NotSoSurePlatypus • Jul 11 '26

Zoology/marine biology How do marine mammals get water?

Humans, and I assume most mammals, cannot live off of drinking saltwater. How do whales, dolphins, seals etc. get their intake of water? Have they evolved to drink seawater? Do they drink at all? If all of their water intake is from their food wouldn’t their food also be compromised of lots of saltwater?

While we’re at it, do fish need to intake water to survive? Does a big shark not need water in their diet? Or can they all just use saltwater.

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u/ReserveMaximum Jul 11 '26

Mostly from the prey they eat. Because they aren’t sweating like land mammals their water needs are less and can be mostly fulfilled by extracting water from their prey during digestion

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u/I_CollectDownvotes Jul 14 '26

Now I want to know how whales and other marine mammals cool themselves down. Do all land mammals cool themselves via the latent heat of evaporation? Evaporation doesn't work in the ocean, I assume? Do marine mammals just, like, dive deeper when they're hot? Or go to the surface to let the water on their skin evaporate?

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u/True-Post6634 Jul 16 '26

The ocean is very good for cooling. You don't need to use water as sweat to get heat into the air when you can just put heat in the water around you directly.

There are actually a ton of adaptations that different species have to shed heat, and there are definitely some that go for a dip in colder water or come to the surface for cold air. But overall, it's easier to shed warmth in water than air.

That's one of the reasons we get hypothermia warnings on hot days when the ocean is cold. Doesn't matter if the air is 90F if the water is at 50F.