Jul 25, 2024 4 min read

A Whale of a Drink

Finding balance in a saltwater bath

A group of humpback whales gulping down mouthfuls of anchovies and seawater. Photo by Don Baccus

The other day I thought of a quirky question that led me down a little rabbit hole: How in the heck do whales find freshwater to drink? And if they gulp down mouthfuls of saltwater every time they eat, how do they deal with all that salt?!

feeding humpback whales — Whales eat by opening their huge mouths and swallowing 10-20,000 gallons of water, greatly expanding their mouths along folded lines of skin (visible on whale at left), then forcing the water out and trapping food behind plates of baleen. Photo by Don Baccus

All animals face the critical challenge of maintaining a narrow balance of water and salt in their bodies (the osmotic balance). Any time there is an unequal concentration of salts across a cell membrane, water must move across the membrane in the direction that balances out the salts. This flow of water in our bodies can end up diluting or concentrating our bodily fluids, potentially leading to a cascade of harmful effects or death if not quickly corrected.

Think about how we constantly try to find the right balance between drinking and urinating; or, if we're exercising and losing salts through our sweat, think about how we need to drink additional electrolytes to rebalance the salts in our bodies. This is essentially what all animals must do every day.

Now imagine the challenges that large mammals living in saltwater must face.

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Fortunately for whales (and other cetaceans) they have had approximately 50 million years to come up with some elegant solutions. One solution is that whales typically move slowly and calmly, lowering their loss of water and giving them time to absorb a bit of moisture through their lung tissues as they hold their breath (a whale that is chased or exerted will soon exhaust its reserve of water).

humpback with calf — A mother humpback whale and her calf finding time to play. Photo by Don Baccus

But extracting moisture from the air doesn't provide enough water for such a large mammal, and it turns out that whales get most of their freshwater from the foods they eat. Fish, krill, and plankton contain high levels of freshwater— often greater than 90 percent of their weight—and whales eat a lot of these foods (10-20 tons a day for blue whales).

Whales will also swim at the surface and drink freshwater during rainstorms, or swim around the mouths of rivers or near melting icebergs. It's believed they might also be absorbing some of this freshwater through their skin.

If they still haven't gotten enough freshwater, whales can make up the difference by swallowing mouthfuls of seawater and using their unique reniculate kidneys to remove the salt. These multi-lobed kidneys resemble a bunch of grapes and are so effective at eliminating salt from a whale's body that their urine is twice as salty as the ocean.

A humpback whale migrating along the California coast at Monterey Bay. Photo by Don Baccus

Even with all these adaptations, whales must still be careful because there are no backup supplies of freshwater in the middle of the ocean, and there are times when they need to rely on all their resources to maintain the right balance.

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I want to express my gratitude to Don Baccus and Kate Spencer of Fast Raft Ocean Safaris for sharing these remarkable photos. Based on California's Monterey Bay, Fast Raft offers one-of-a-kind outings where you can view one of the world's great concentrations of whales at water level. Monterey Bay is renowned because it's where a deep submarine canyon occurs within a mile of the coastline, pushing nutrient-laden waters to the surface and fueling a highly productive ecosystem that attracts huge numbers of marine mammals and birds within minutes of the dock. You have to see it to believe it!