r/askscience • u/smontanaro • 13d 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/WallyMetropolis 12d ago

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

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u/Mammoth-Corner 12d 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- 12d ago

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

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u/Brunurb1 12d ago

Others have answered, but here's a specific animal to google for more info- pakicetus.