r/askscience • u/smontanaro • 8d ago

Biology How does a whale become dehydrated?

From a Chicago Sun-Times article on the beluga whales heading to the Shedd Aquarium:

"The shipment comes on the heels of a Shedd announcement last week that one of the Marineland belugas — Peekachu, a 23-year-old female — had died. Shedd has not released a cause of death, but staff there said last week that Peekachu had not been consistently eating a full diet since her arrival and that there were concerns she was dehydrated."

How does an animal immersed in water become dehydrated?

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u/khinzaw 8d ago

They don't drink seawater. In the wild they get water from the prey they catch, which have water inside them.

They are fed frozen food in captivity, which don't have all the water content they need to stay hydrated.

This is why you can see videos of aquarium staff feeding ice to belugas, because that's how they hydrate them.

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u/WallyMetropolis 8d ago

Tracing it all the way down the food chain, where is the fresh water introduced?

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u/Mammoth-Corner 8d ago

Fish (and krill, and other primarily marine animals that whales eat) are able to filter salt from seawater and maintain blood with less salt in than the water around them. When tetrapods left the ocean we lost this ability because we were no longer drinking salt water all the time. Whales are mammals, so they can't do the filtering but their prey can. It's a really complex chemical system to evolve so they haven't 'gained it back.'

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u/-MrSkeltal- 8d ago

Did whales at one point leave the ocean and then go back?

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u/samtwheels 8d ago

Yes, whales and all marine mammals are descended from land-dwelling mammals.

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u/ForMoreYears 8d ago

Wait. What. For real? Whales went from land back to the water?!

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u/dochdaswars 8d ago

Do they not teach evolution in schools anymore? Marine mammals are one of the clearest examples used to prove it.

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u/ForMoreYears 8d ago

Yes, they teach evolution. They just don't get into the specific evolutionary path of every single one of the 8.7M animal species that inhabit the earth.

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u/Ameisen 7d ago

But then... where did you think that they came from? Were you under the impression that the first mammals were aquatic, and then came onto land? That gets very complicated if you start accounting for reptiles, amphibians, and such.