How Do Sharks Survive in Freshwater?

Bull sharks can live in freshwater.

Bull sharks can live in freshwater.

Most people associate sharks with saltwater and the oceans, and rightly so. However, while saltwater environments are certainly where the great majority of shark species can be found, this is not to say that they are completely unable to survive in freshwater environments as well. In the United States alone, sharks have been spotted in the Mississippi river as far north as Illinois, as well as in the ocean-connected rivers that are so prevalent throughout South Florida and the Everglades.

This is not to say that you will find just any species of shark making its way into the world’s freshwater rivers. In fact, there is one shark in particular who seems to be found in these areas more than any other – the bull shark. Furthermore, this fact can be particularly scary when you consider that bull sharks are responsible for more human deaths than any other species of shark in the world. Not only must swimmers be wary of alligators when entering a Florida river, but if said river is also connected to the ocean, swimmers must also be careful to avoid bull sharks as well.

Scientists are still not entirely sure what makes this special characteristic almost exclusive to this single species of shark. All species of sharks must maintain a certain concentration of salt within their bodies, as salt prevents their cells from rupturing which in turn causes bloating and death. As soon as a shark enters freshwater, the salt concentration within their body becomes diluted, which is why the great majority of sharks will never even enter freshwater at all, or if they do, will leave it almost immediately.

The fact that bull sharks can live in freshwater is not because they do not possess the same need to maintain a certain salinity level as other sharks. Bull sharks still need to maintain their salinity levels, but have developed a special ability within their kidneys to continuously recycle and retain the salt that they absorb. And while it is not yet known how or why they developed this ability, it does seem to give them a competitive advantage when it comes to feeding and breeding, allowing them exclusive access to certain prey as well as a safe haven for newborns. However, because freshwater environments still do not appear to be preferable for bull sharks, it is clear that the disadvantages of such environments still outweigh the advantages.

For your chance to see two of planet earth’s most fearsome predators in the same environment – alligators and sharks – take an airboat ride through the Everglades today. Not only are airboat tours a safe way to observe these wild animals from a comfortable distance, but they are a great way to explore everything else that the Everglades has to offer as well.

Bull Sharks in the Everglades

bull sharks

A bull shark in the water.

Alligators and crocodiles are not the only apex predators that call the Florida Everglades home, though they are undoubtedly the most well known. Many people might actually be very surprised to learn that sharks also live in the Everglades, especially because it’s such a commonly understood fact that sharks need saltwater and are therefore restricted to the world’s oceans.

This fact, however, is a myth, as there are a few species of sharks that are able to adapt to and live in freshwater. Most notably, bull sharks, which have been found in rivers as far north as Illinois. Because many of the wetlands and swamps of the Everglades are connected to the Gulf of Mexico and Atlantic Ocean, it should come as no surprise that bull sharks have been known to find their ways there.

Bull sharks and other freshwater sharks are able to easily adapt to saltwater or freshwater environments because they possess an ability called osmoregulation. While all sharks have this ability, which is simply the ability to maintain a certain concentration of water within the body, bull sharks are different in that they can gradually adjust their kidneys to suit different levels of salinity depending on what kind of water they are in.

Next time you’re out on an Everglades airboat ride, keep your eye out for some fins in the water as well as the usual scales. Because bull sharks are especially prevalent during birthing season, when the secluded rivers of the Everglades provide the perfect protection for young pups, now is the perfect time to spot creatures of all kinds on an Everglades tour.