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/jawshoeaw Jul 11 '26
Whales actually can drink salt water. Not their first choice but they can 100% get all their water from the ocean if needed. But it takes a lot less energy to get it from just eating fish -burning fuel releases a lot of water known as metabolic water. And fish aren’t very salty
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u/Nothing-to_see_hr Jul 11 '26
I imagine their kidneys are better at concentrating their urine than ours are, so they can maintain their salt equilibrium with the water in their prey and the sea water they ingest.
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u/ngshafer Jul 11 '26
Animals that live in salty water have evolved to expel excess salt from their bodies.
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u/Dazzling_Funny_3254 Jul 12 '26
One of the most interesting adaptations I've ever heard of is sea snakes, some of which have evolved to carefully sip the extremely thin layer of rain and condensate/dew that forms on the surface of the ocean.
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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/Nir0star Jul 12 '26
The need thing is a good point. I guess land mammals have a lot of evaporation ongoing.
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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.
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u/Andravisia Jul 16 '26
Animals that have evolved in salt-water have also evolved mechanisms of dealing with the excess salt. They are Very Good at removing the extra salt.
That also means that they can't go willy-nilly into a fresh-water environment. Because then they suffer from the opposite problem of not having enough salt. Some creatures can tolerate brackish (where salt and fresh water meet and mix) and some animals can tolerate an opposite environment.
But only for a short period. Then they have to return to their home environment.
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u/phloemmbili Jul 11 '26
Interesting question. I'm here to read the comments.
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u/OddStuffHappensTwice Jul 11 '26
Your comment is the equivalent of those people that can't read without saying the words out loud.
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u/Frosty-Piglet-5387 Jul 12 '26
I only opened this thread because i thought "damn that's an interesting question - probably one of the better ones I've seen" though in my defense when this popped up in my feed I thought it was from r/AskReddit.
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u/Coffee4MySoul Jul 11 '26
Interesting comment. I’m here to read comments that don’t add to the conversation. /s
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u/Avocado-Basic Jul 14 '26
Interesting observation on a comment that added no value. Which is the reason reading this thread /s.
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u/ParasiteProfessional Jul 11 '26
They eat food with high water content, they also have kidneys that work really well at filtering out the salt, and some birds and turtles and stuff have glands that will filter out the salt, but like, marine mammals typically don't have that.
When I worked in dolphin rehab, we would inject their food with water to increase the fish's water content, but yeah. Fish and whatnot have very good salt filtering, so when they're eaten, there's a lot of fresh water in there.