How can sea mammals drink saltwater?
Marine biologist Robert Kenney of the University of Rhode Island offers the following explanation:
DOLPHINS and other sea-dwelling mammals can obtain water from their food and by producing it internally from the metabolic breakdown of food.
Although some marine mammals are known to drink seawater at least on occasion, it is not well established that they routinely do so. They have other options: sea-dwelling mammals can get water through their food, and they can produce it internally from the metabolic breakdown of food (water is one of the by-products of carbohydrate and fat metabolism).
The salt content of the blood and other body fluids of marine mammals is not very different from that of terrestrial mammals or any other vertebrates: it is about one third as salty as seawater. Because a vertebrate that drinks seawater is imbibing something three times saltier than its blood, it must get rid of the excess salt by producing very salty urine. In the seal and sea lion species, for which measurements exist, the animals' urine contains up to two and a half times more salt than seawater does and seven or eight times more salt than their blood.
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Salt and water management in mammalian kidneys is a two-step process. First the blood passes through a microfilter system in a part of the kidney known as the glomerulus. Most of the blood plasma, including water and small molecules like salts, passes through the filter, but the larger molecules, as well as the blood cells, are held back. The filtered plasma then passes through a long tube called the loop of Henle, where the water is reabsorbed. This process concentrates the remaining fluid, which is finally excreted as urine. One popular theory holds that a simple modification of the standard mammalian kidney¿namely, longer loops of Henle¿allows marine mammals to produce a more concentrated urine by reclaiming more of the water. Kidney anatomy in manatees and harbor porpoises seems to support this theory, but it has not been closely studied in most marine mammal species.
SEALS drink seawater at least on occasion. But some will eat snow to get fresh water.
A marine mammal can minimize its salt and water balance problems by following the same advice my doctor gave me to keep my blood pressure down: avoid salty food. With the exception of the herbivorous manatees and dugongs, all marine mammals are carnivores. Different food types vary in salt content. Species that subsist on plants or invertebrates (such as crustaceans and mollusks) consume food with about the same salt content as seawater. These species thus face the same salt removal problem they would have if they drank seawater directly. 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.
FAQs
Although people can't drink seawater, some marine mammals (like whales and seals) and seabirds (like gulls and albatrosses) can drink seawater. Marine mammals have super efficient kidneys, and seabirds have a special gland in their nose that removes salt from the blood.
How can sea mammals drink salt water? ›
A. Marine animals may consume both freshwater and saltwater. They rely on various adaptations for survival when only saltwater is available. Many marine mammals have specialized organs called reniculate kidneys with multiple lobes, increasing their urine-concentrating efficiency beyond that of humans.
Can mammals live in salt water? ›
Cetaceans are marine mammals, which are adapted to living in the salt waters of the various seas and oceans of the world. ... For example, bottlenose dolphins can vary the concentration of their urine when they move from salt water, their natural habitat, to freshwater.
How do marine mammals absorb water? ›
Most marine mammals rarely drink fresh water; instead, they: Utilize water present in their food, inspired air, and blubber. Have specialized kidneys that produce urine that is saltier than seawater.
How have marine mammals adapted to consuming high salt content foods? ›
Each of these reniculi function like a mini kidney, increasing their ability to filter and excrete excess salt. Marine mammals also have a thicker medulla in their kidneys, which allows them to reabsorb more water with much more efficiency, further concentrating their urine to excrete more salt.
How can animals drink salt water? ›
Although people can't drink seawater, some marine mammals (like whales and seals) and seabirds (like gulls and albatrosses) can drink seawater. Marine mammals have super efficient kidneys, and seabirds have a special gland in their nose that removes salt from the blood.
Why can't mammals drink salt water? ›
The high salt content burdens their kidneys, which play a crucial role in eliminating metabolic waste from the body. This applies not only to dolphins but also to humans and other marine mammals. In mild cases, dolphins ingesting excessive seawater may experience dehydration, weakness, and fatigue.
How do whales drink salt water? ›
The massive size of the whale's kidney and its efficiency allow it to filter out the salt without sacrificing the water their bodies need.
How do seals drink salt water? ›
Like all marine mammals, seals get all the water they need from their food. Their bodies are very efficient at removing and recycling water from their food. They avoid drinking sea water; if a seal drinks too much sea water it can become seriously sick.
How do dolphins drink salt water? ›
The answer is: they do not drink water like land animals do, as they don't risk dehydration from the sun. This goes for all the marine mammals like whales, dolphins, seals etc. The way they get water is through their food.
Soaking in Salt
So fish need to drink lots of seawater to stay hydrated. And because seawater is so salty, they also must pump out the excess salt, both through their kidneys and using specialized cells in their gills.
How do marine mammals sleep without drowning? ›
So how can they sleep and not drown? Observations of bottlenose dolphins in aquariums and zoos, and of whales and dolphins in the wild, show two basic methods of sleeping: they either rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal.
Can marine mammals survive out of water? ›
Cetaceans belong in the sea and being too long on land can lead to fatal exposure – like a human in a desert. Without the support of water, the sheer weight of larger species can also simply crush their internal organs, leading to death.
How do whales survive drinking salt water? ›
The Process to Filter out Sodium
Our kidneys are not equipped to drink salt water, but whales' kidneys are. The massive size of the whale's kidney and its efficiency allow it to filter out the salt without sacrificing the water their bodies need.
How do whales stay hydrated in salt water? ›
Staying Hydrated
Even though they can drink salt water, whales are thought to get the bulk of the water they need from their prey - which includes, fish, krill, and copepods. As the whale processes the prey, it extracts water. In addition, whales need less water than we do.
How do sharks drink salt water? ›
Instead of drinking water, the shark absorbs some seawater (and salt) through its gills. A glandin the shark's digestive system gets rid of excess salt.
