How can dolphins drink salt water

When this balance is lost, we refer to osmotic stress. This is the case when there is an increase in water evaporation, as it triggers an increase in salt concentration in the body. How do marine mammals manage to hydrate with salt water? Through special adaptations that they have developed, unlike the majority of land mammals. Indeed, the kidneys of marine mammals are so effective that the latter are capable of excreting a urine that has a higher salt concentration than the sea water itself and are thus able to access a supply of fresh water by ingesting salt water.

But how is it possible to know when a marine mammal drinks sea water, and how much? Researchers can measure the amount of sea water ingested by an organism using isotopic tracers. These tracers are atoms that are introduced or already present naturally in water, which can be differentiated and detected thanks to their mass.

Researchers add the amount of water ingested by food intake and metabolism, and then compare that amount to the total amount of water passed into the body. Several factors must be taken into account for these calculations.

Moreover, salt intake from prey varies depending on the diet. Thus, the ingestion of invertebrates such as squid or krill results in a higher salt intake into the body than the consumption of fish. This is why researchers must know precisely what the organisms are eating. Under certain nutritional conditions in captivity, they have thus demonstrated that some species, such as the hooded seal or the short-finned pilot whale, may drink salt water.

In one of the more vexing ironies about human life on Earth, we rely on water for life, yet Where did we go wrong?? But what about whales, dolphins, sea lions and other marine mammals?

Did they figure this out a little better than we did? They live in saltwater; but do they also drink it? Marine biologist Robert Kenney of the University of Rhode Island explains that some marine mammals have been known to occasionally partake in the salty stuff, but they rely on other options.

The often get the water they need from the food they eat, very clever. The New York Times writes that they can get low-salt water from dinner: "Whales, for example, have the specialized kidneys but need far less water than land mammals. Whales get water mostly from the small sea creatures, like krill, that form much of their diet. Marine mammals can also produce non-salty water on their own from the metabolic breakdown of food, says Kenney, as "water is one of the by-products of carbohydrate and fat metabolism.

Even so, marine mammals get a lot of salt Seawater is three times saltier than blood of both terrestrial and marine invertebrates. So sea animals get rid of extra salt by producing super salty urine. Kenney explains that in some seals and sea lions, for example, their urine contains up to two and a half times more salt than seawater does and seven or eight times more salt than their blood.

Some seals will eat snow to get their fresh water; meanwhile, California sea lions can get enough water from the fish they eat and can live without actually drinking any fresh water at all.

And while you might think that seabirds have it easier, given that their gift of flight can take them out of the sea and to freshwater sources, they still have some pretty nifty tricks up their wings. In contrast, marine mammals that feed on fish consume food with a salt content similar to that of their own blood, thereby avoiding the problem entirely. Indeed, a study of California sea lions showed that, on a diet of fish, these animals can live without drinking fresh water at all.

Some species of seals and sea lions apparently do drink seawater at least occasionally, as do common dolphins and sea otters, but the practice is very rare in some other species. When given the choice, manatees and some pinnipeds will drink fresh water. People who live on salt or brackish waterways in Florida sometimes leave a garden hose flowing into the water in order to see the manatees come to drink.

Likewise, some seals will eat snow to get fresh water. For most whales and dolphins, however, we simply do not know how they get their water, because it is difficult to observe these animals. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.

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