How do baleen whales drink fresh water, is that because of krill?

Answer

The salinity of the blood and other fluids in that of whales and other marine mammals is not much different from that of land mammals. It is about three times less salty than seawater.

A mammal that drinks seawater must therefore get rid of this excess of salt.

This can be done by producing urine that is more salty. In seals and sea lions, the urine can be 2 to 3 times saltier than the original water. The amount of water and salt in a mammal’s body is regulated in the kidneys.

How does this happen?

When you eat or drink it ends up in the stomach. The water is absorbed by the body in your stomach. This water is both the water you drink and the water in your food (more specifically in the cells). Salt is also simply included here. This increases the salt content in your body. The circulatory system and your kidneys play an important role in regulating the salt level in your body.

In the kidneys, plasma from the blood is first filtered: water and small molecules such as salt pass through this filter, while large molecules and blood cells remain in the circulation. After this, part of the water and substances are reabsorbed into the bloodstream. This happens around a type of tube called Henle’s loop. In marine mammals this tube seems to be much longer so that more ‘fresh’ water can be absorbed back. But this is indeed not ideal, so it is better to ensure that you do not ingest too much salt or salt water. That is why marine mammals do not drink seawater.

So it is better to limit the amount of salt you get in and not to drink salt water.

Animal foods have the same salt content as marine mammals. The water that is extracted from this food therefore has the “right” amount of salt. So the kidneys don’t have to work so hard. Since krill is also much less “salt” than the seawater, it is therefore a good source of water for baleen whales.

Little is known about the correct mechanisms in whales. After all, these animals are difficult to study.

There is another way to get water. Water (H2O) can also be obtained by the body from biochemical compounds such as carbohydrates (Cm(H2O)n and fat. This occurs as part of the metabolism. Fats and carbohydrates are also common in animal foods and also in krill.