When we think of sharks, we usually think of the ocean, because that is primarily where sharks live. Many people especially connect sharks with the kind of wild and open ocean you find at the beaches of, for example, Florida and California. Since we also typically think of sharks as large creatures, although there are several tiny shark species, it makes sense that we associate them with the open ocean.
Rivers, a Place Where Sharks Live
But not all sharks live in the ocean. A few shark species live in rivers. They are known as river sharks, and their genus is Glyphis, which belongs in the family of requiem sharks. There are currently three recognized species of river sharks: the Ganges Shark, the Northern River Shark, and the Speartooth Shark. The Borneo River Shark and the Irrawaddy River Shark are also river sharks, but it is thought that they should be considered the same species as the Ganges Shark. In addition, the Bull Shark is able to live both in saltwater and in freshwater, and can be found in rivers, although it is not considered a true river shark.
The Elusive River Sharks
The river sharks are shy and secretive, so it is possible that there are other species of river shark that we have simply not been able to observe and describe yet. They are also endangered, the Northern and Ganges River Sharks being critically endangered. Because they are rare and difficult to observe, we can’t be sure of their geographical reach, but they have been found in South and Southeast Asia, New Guinea and Australia. The Bull Shark can be found in the Atlantic from the Americas to Africa, as well as in the Indian Ocean from South Africa to Vietnam and Australia, including in the rivers associated with those locations.
How Big Are River Sharks?
Contrary to what you might expect, the river sharks are not among the tiny species of sharks, but nor are they among the largest. At maturity, the Ganges Shark is around 2 m (6.5 ft). For the Northern River Sharks the males are a little smaller than the females, with the males reaching 1.4 m (4.6 ft) and the females 1.7 m (5.6 ft). The Speartooth River Shark is the largest of these species, as it can reach 2.6 m (8.5 ft). The Bull Shark is similar in size at 2.4 m (7.9 ft). So these are quite large creatures to encounter in a river, except they rarely let you see them.
The Ganges River Shark
The famous Ganges River of India gave its name to the Ganges River Shark. The shark lives in other Indian rivers too, and under the names Borneo River Shark and Irrawaddy River Shark it also lives in rivers of Pakistan, Myanmar, Borneo and Java. It is a typical requiem shark, stocky, greyish brown with a broad snout and small eyes. The eyes are unusual not just for their small size, but also because they point upwards. It is thought that the eyes are adapted for poor visibility, and that the upward tilt is so the shark can hide deep in the river and look for prey above. The shark has sharp and slender teeth, which means that the shark most likely feeds mainly on fish.
The Northern River Shark
The northern areas of Australia are home to the Northern River Shark, which is how it got its name. The shark has also been found in Western Australia and Papua New Guinea. The species is named for Jack Garrick – the first ichthyologist who found the species. The shark is similar in appearance to the Ganges River Shark and has the same small eyes. The Northern River Shark also has an unusually high number of ampullae of Lorenzini, which are electroreceptors that help the shark identify its prey. This is most likely also, like the eyes, an adaption for hunting fish. The shark is extremely rare and it is estimated that only 250 specimens exist in the wild.
The Speartooth River Shark
Also found in Northern Australia and New Guinea is the Speartooth River Shark. Similar in shape to the other river sharks, the Speartooth is grey, rather than greyish brown and has a black spot below each pectoral fin. It gets its name from the spear-like teeth in its lower jaw. It has the same small eyes and adundance of ampullae of Lorenzini as the other river sharks, suggesting that it hunts by “shark radar” more than by sight.
The Bull Shark
Although the Bull Shark is not a true river shark, it does enter rivers and other freshwater areas. It can go quite far up rivers, but must return to saltwater in order to breed. Like the river sharks it is a requiem shark. The Bull Shark eats fish, other bull sharks as well as various small animals, like turtles and birds. It is an aggressive shark and has been known to attack humans. Unlike the river sharks, it is not endangered and it can be found worldwide.
Research and Protection Are Needed
So, it is not necessary to go out to sea to encounter sharks. But if you want to observe river sharks in their natural habitat, you may need a lot of patience before you find one of these rare and elusive creatures. The true river sharks have many characteristics in common, including being endangered and poorly described, it is critical that more research be done, and that protection be put in place before they disappear all together.