In the Rivers and Lakes: An Overview of the Freshwater Sharks
Mattawan Creek in New Jersey is a few miles away from the Atlantic Ocean. This narrow and shallow freshwater creek is the last place one would expect to find sharks lurking under its surface. However, in 1916, this realization came to fruition with tragic consequences.
A boy and a man (who tried to save him) were attacked and killed by what many experts believed was a 10-feet long bull shark. The murky water of the creek camouflaged the shark. And, eventually, allowed it to slip away into the muddy water, and possibly back out to sea.
The event at Mattawan Creek was a rarity. Simply put, shark attacks don’t happen on a current basis. In addition, they don’t happen all the time in rivers and lakes.
Still, these events reveal something else about the nature of sharks: they can adapt and exist in almost any waterway. Eyewitnesses spotted sharks in major rivers such as:
- South Africa’s Zambezi River,
- Australia’s Fitzroy River,
- India’s Ganges,
- South America’s Amazon, and
- North America’s Mississippi River and connecting rivers.
Unsuspecting anglers hooked them; witnesses on the shore spotted their distinctive dorsal fins and tails; and – on those rare occasions - swimmers have been attacked in waterways not commonly known as hunting grounds for one of nature’s most fearsome underwater predators.
Incredibly, those sighting are outliers. Most freshwater sharks elude detection. Freshwater sharks are not what they always seem to be. While large apex hunters enter these ecosystems from the oceans, the small docile species exist anonymously in nearly secluded and/or murky waters.
Real Freshwater Sharks
First, there needs to be a clarification; there are “real freshwater sharks” and another species of fish mistakenly referred to as “freshwater sharks”. Real freshwater sharks are bull sharks and the five species of river sharks known as Glyphis.
The “non-shark” looks the part but lacks the ferociousness and size one expects from a shark. Cyprinids are freshwater fishes with bones (something sharks don’t have), which consist of carps, minnow, barbs, and barbells. If anyone wants to know where to find these “boney sharks” one can take a trip to the local pet store and observe the following:
- red-tailed shark,
- bala shark,
- tricolor shark, and
- silver shark.
Now, about the real freshwater sharks: Bull sharks bide their time in salt and fresh water areas; where as sharks such as the Ganges Sharks are found primarily in the freshwater domains of the Ganges.
The real freshwater sharks frequent rivers in the tropical zones. However, there have been recent cases of Greenland sharks spotted at the mouth of the St. Lawrence and Saguenay River in Canada (marinebiodiversity.ca). Also, there is a reported incident of a bull shark being caught in the Mississippi River as far upstream as Illinois (NOAA, 2011).
Freshwater sharks are unique from their seawater counterparts. With the exception of the bull shark, seawater sharks can’t survive in a freshwater environment. This fact was demonstrated in 2011 when hundreds of leopard sharks washed ashore throughout the San Francisco Bay area.
State biologists investigating the situation soon discovered the cause; excessive freshwater flowing into shoreline lagoons – the sharks’ mating and feeding grounds - from rain-swollen rivers and streams. It is believed that freshwater threw the sharks’ body chemistry off balance, with fatal results ( Zito, 2011).
Bull sharks are one of the most aggressive predators in salt and freshwater. They are one of the three sharks implicated in unprovoked fatal attacks throughout the world (NOAA, 2011). They’re found in shallow coastal waters such as lagoons, bays, and river mouths.
In South Africa, Australia, South America, and Asia, bull sharks commonly swim and hunt in major river systems. Their diets include fishes, sharks, dolphins, turtles, birds, crustaceans, and terrestrial mammals (Shandiya, 2011). Humans are not usually on their lists. However, they injured or killed humans through their use of the bump-and-bite technique.
The tenacity of the bull shark has been made apparent in South Africa and Australia. In Australia, bull sharks didn’t just roam up rivers, they made it to reservoirs and lakes where they attacked livestock as large as horses, as well as humans.
In South Africa, they are known as Zambezi River sharks or Zambi. They’ve had a nasty reputation and are feared by locals (even though the crocodiles in this river have killed more people than the shark). They’ve been spotted nearly 100 miles upstream.
Due to its wide range and habitats, the bull shark are known by various names such as Ganges River shark, Fitzroy Creek Whaler, van Rooyen’s Shark, and Lake Nicaragua shark (Wikipedia, 2011).
The Glyphis or River Shark
Despite the bull shark’s ability to survive in freshwater, it is not considered a true freshwater shark, since they are usually found in saltwater. River Sharks, or the Glyphis, are the only species to live primarily in freshwaters. They are rare, and little is known about them. There are five species found in the brackish waters of Asia and Australia.
Many of these sharks are misidentified as being bull sharks. Others are so rare that only a few specimens ( and a few eye witness reports) exist to confirm their existence. Some do not have official names, yet. Researchers speculate that they are primarily fish eaters. The sharks are:
Ganges shark: found in the Hooghly-Ganges river system of the Indian subcontinent. Considered dangerous; however, they reside in the same area as bull sharks. Not to be confused with the bull sharks that inhabit that area and goes by the same name.
Speartooth Shark: found in the rivers of Borneo, New Guinea, and Queensland Australia.
Irrawaddy River Shark: found in the Irrawaddy River near Rangoon (Miramar).
Glyphis species A: two specimens found in estuary waters of the lower Bizant River in Queensland, Australia, and possibly seen in the Alligator River system of Northern Territory, Australia.
Glyphis species B: one specimen found in the Kinabatangan River in Borneo. This particular shark was believed to have been extinct since the 19th century until a specimen was recently found.
Glyphis species C: nine specimens collected from Australia’s Adelaide River and South Alligator River between 1989 and 1999 (ReefQuest Centre, 2011).
These sharks are described as being short, having a broad rounded snout; small, wide-spaced nostrils; small, dark eyes; broad, serrated upper teeth; short labial furrows; broad dorsal fin with mid-base closer to the base of the pectoral fin; and an anal fin with a deeply notched posterior margin (ReefQuest Centre, 2011).
Many of these sharks are on the endangered species list. Just as overfishing has affected the habits of ocean-going sharks, the same holds true for river sharks. Many of these species are on the verge of extinction.
Sharks by nature are predators and prey on aquatic animals. While shark attacks in the ocean -- as well as the river -- are rare, they do occur when humans happen to be in the wrong place at the wrong time. It’s hard to say if all river sharks are a threat to humanity; however, if history has shown correctly, these sharks have more to fear from humans rather than seeing them as preys.
Extra: Story of a Real Photo From a Fake Story on Freshwater Sharks
Some may have heard of the story of a shark being caught in a lake in northern Texas. A story about the Lewisville Lake shark went viral last June. It claimed that an angler caught a shark in the lake, and as proof took a picture of the shark with his granddaughter kneeling in front of it. Also, it stated that Texas officials warned swimmers at a nearby lake about possible sharks lurking in its water.
It didn't take long for the story to be debunked (it originated from a prank site). Still, the photo is real. According to the website for ABC affiliate in Dallas (WFAA), the picture was taken in August 2013 at Buzz's Marina in Maryland. And, it was reported that "fishermen really did catch two large bull sharks near the mouth of the Potomac River."
The granddaughter was real too.
"That's our grand daughter Savannah," Christy Henderson of Maryland was reported as saying to a WFAA reporter.
© 2018 Dean Traylor