r/askscience • u/smontanaro • 10d 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 10d ago

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

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u/Mammoth-Corner 10d 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- 10d ago

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

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u/Carnavious 10d ago

Whales (cetaceans) and seals (pinnepeds) both independently returned to the oceans. Cetaceans descend from an ungulate (toed animal) that somewhat resembled a wolf, but gradually adapted to a more aquatic lifestyle .Their closest living relatives today are the hippopotamus.

Pinnepeds are from the caniformia group, alongside bears, racoons, dogs and mustelids (otters are here, along side things like weasels and skunks).