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Matt: How come if a human being drinks seawater he’ll probably get sick and die, but whales, dolphins, and walruses, and penguins can drink ocean water and thrive on it?

— Curious Bob, University City

Yeah, a cup or two of Mission Bay water would do you in, that’s for sure. I’m not even positive a walrus could handle it. But I have a surprise for you. Most marine mammals don’t drink salt water. They couldn’t deal with a constant diet of Pacific Ocean either. Scientists are a little bit in the dark about the drinking habits of whales and some dolphins, since they’re hard to observe in the wild. But since the mammals need water, how do they get it? From the fish they eat. Fish are low-sodium tidbits, so marine mammal kidneys can handle it. In fact, they can extract water as they metabolize the fish to satisfy their needs. The salt content of marine mammals’ blood is not so different from the blood of terrestrial critters.

Sea otters, seals, sea lions, and manatees have been observed occasionally drinking seawater. But they’re capable of concentrating and excreting highly salty urine, so they can handle it. Any creatures (including birds, sharks, and snakes) that live in or even near a saltwater environment have some method of getting rid of excess sodium. For that matter, so do all marine fish. Too much salt apparently doesn’t do anybody any good.

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