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When we think of sharks most people immediately assume that they can only be found in the sea. Well, think again, because there are actually several shark species that lurk in rivers. Some spend their whole lives in fresh water while others just come and go, but what’s most fascinating is their ability to adapt to an environment they shouldn’t physically be able to live in. Join us and find out exactly which sharks can live in freshwater and how they do it.
6. Ganges shark
Ganges sharks are real river sharks. This means that they have adapted to live in a freshwater environment and do not stray into saltwater at all. Although originally thought to inhabit only the rivers Ganges, Hooghly and Brahmaputra in India and Bangladesh their range has recently expanded. This is because the river sharks of Borneo and Irrawaddy have been reclassified as subspecies of the Ganges shark, rather than being their own individual species as originally thought. Ganges sharks grow to between 5 and 6.5 feet in length and spend most of their time swimming at the bottom of the rivers while scanning the water above for prey.
Sharks don’t have a swim bladder, so they rely on their oil-filled livers to help them float instead, because the oil is lighter than the water. Saltwater has more buoyancy than freshwater, so to compensate for freshwater sharks, they need much larger livers to hold more oil to keep them afloat. As a true river shark, the Ganges sharks are adapted to their environment as they have much larger livers than other sharks. This is why river sharks tend to have thicker bodies than sea sharks.
In addition, most sharks contain a lot of salt – so much that they are slightly saltier than the sea. This allows them to keep their salt in while regularly taking in water through their gills and filtering out what they don’t need. However, when they are in fresh water, the salt in their bodies is diluted and their kidneys work harder to get rid of it. This weakens the sharks, causing dehydration and eventually death. River sharks contain less salt so they don’t have this problem.
5. Bull shark
The exception to the rule that marine sharks cannot stay in freshwater for extended periods is the bull shark. Bull sharks do not have as much salt in their bodies as other sea sharks. This makes it much easier for them to spend time in fresh water, although their kidneys are still working hard to get rid of the extra fresh water they ingest. They do this by urinating up to twenty times more in fresh water than in salt water. Also, their livers produce urea when needed, depending on the salinity of the water they are in. This means that bull sharks have the ability to regulate their bodies to live in fresh or salt water.
Bull sharks are easily the most dangerous sharks to live in freshwater. They are large sharks with stocky bodies about 3 meters long. They live worldwide in coastal areas, lakes and hundreds of miles upstream in rivers. A chilling sight was when bull sharks were caught swimming through the streets of Brisbane when the area was flooded in 2010. Not only that, there’s even a shark-infested golf course in it Australia at! Bull sharks entered the lake at the Carbrook Golf Course after local rivers flooded in 1996 and have been trapped there ever since. However, the population seems to be doing just fine as there are currently about a dozen bull sharks, making retrieving any stray golf balls a very bad idea.
Bull sharks have a large number of recorded attacks. It is even believed that they were responsible for the deadly attacks on Jersey Shore in 1916, which inspired the jaws novel. Two of the attacks took place inland in the Matawan Creek, which points to a shark that can tolerate fresh water.
4. Northern River Shark
Despite the name river shark, northern river sharks are mainly juvenile sharks rather than adults that live in freshwater rivers. Northern river sharks have stocky bodies, small eyes and grow to about 2 meters in length. They live in tidal rivers, estuaries and coastal bays in Australia and Papua New Guinea. Northern river sharks generally live in areas with silty and muddy bottoms and poor visibility. Because of this, they rely on electrical impulses to find their prey instead of using their eyesight. Although adult northern river sharks reside in coastal areas, both neonates and juveniles regularly travel to fresh or brackish water and juvenile northern river sharks have been observed in many rivers in Australia. However, the entire population of the species may not exceed 250 adult individuals, making it one of the rarest sharks in the world.
3. Speartooth shark
Although speartooth sharks are called river sharks, they live in both salt and fresh water. Speartooth sharks have streamlined bodies, a broad head with a flattened snout and reach about 8.5 feet. They live in coastal waters and tropical rivers in and around Australia and New Guinea, swim with ease between fresh and salt water. Speartooth sharks have been spotted hundreds of miles upstream in Australian rivers. However, juveniles tend to travel further upstream than adults. Speartooth sharks regularly use the tidal currents to travel upstream and downstream without much effort. They do this by traveling upstream with rising tide and downstream with low tide. Speartooth sharks can live in a range of salinities as they travel between the sea and rivers.
2. Pondicherry shark
Pondicherry sharks are one of the rarest sharks in the world and have been sighted in several rivers in India. They are relatively small – about 3ft 3in – and were thought to be extinct between the 1970s and 2011. However, they were rediscovered in the Menik Ganga River in Sri Lanka in 20
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when one was caught and then released. Because Pondicherry sharks are so rare, little is known about them. Because of this, it is not known exactly how they can tolerate fresh water. Despite this, lately they have been seen more often in rivers than in saltwater. Therefore, it is possible to suggest that they can live longer in freshwater than would be expected.
1. Greenland shark
One of the most unexpected sharks to be found in freshwater is the greenland shark. Greenland sharks are huge sharks – which can grow up to 6 meters in length – and have the longest life span of a shark. They live between 250 and 500 years and most don’t even mature until they are 150. Not only that, they also regularly inhabit some of the deepest parts of the ocean, often diving to depths of over 7,000 feet.
Greenland sharks live in the cold waters of the Arctic and North Atlantic oceans. However, they have also been observed in the Saguenay and St Lawrence rivers in Canada. Little is known about how long Greenland sharks can tolerate freshwater. However, a group of scientists observed a population of them in St. Lawrence that lacked the eye parasites most Arctic Greenland sharks have. This led them to believe that there is a possibility that they are a completely separate population from those living in the ocean.
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