The Shark of the River and Sea
On the Mississippi River, not far from the town of Alton, Illinois, two commercial fishermen set out their traps. Herbert Cope and Drudge Collins were familiar with this stretch of the river, and they had made a modest living hauling out large catfish and other fish using wood and mesh traps. In 1937, however, something began to raid their traps, busting them up and tearing them asunder. The two fishermen built a large wire fish trap and baited it with chicken. They probably thought it was a muskellunge or a gar that was raiding their fish traps. These big fish often raided their traps, and they occasionally caught them. However, the flesh of these fish was as unmarketable as it was unpalatable. Setting the big trap was a attempt to rid their fishing grounds of a trap raider, not the act of catching a market fish. They set the big wire fish trap and left it in the river.
When they hauled the fish trap up, they were shocked to discover that the trap raider was not a big muskie or a gar at all. In fact they were rather surprised to find that their trap raider had a body like a sturgeon. When they finally got a good luck at their catch, they were even more taken aback. Their trap raider was a shark, the likes of which is more commonly seen in the lower Mississippi and the ocean proper. Alton is roughly 1,750 miles up the Mississippi from the Gulf of Mexico, so it was rather shocking that such a beast would have been the fish trap raider. The shark measured roughly five feet in length, and it weighed 84 pounds. However, it was of a species that can get much larger. The shark that the fishermen caught was small bull shark, one of the few species of shark to tolerate fresh water, and some females of the species have been known to reach weights of 500 pounds.
The River Shark
Rivers throughout the world have a name for a shark that dwells within it. In Southern Africa, it is the Zambezi Shark. In Nicaragua, there is the Lake Nicaragua shark. In India, it is called the Ganges shark. In Australia, it is called the Swan River shark and the Fitzroy creek whaler. All of these sharks are local names for the bull shark, which swims up these river, and in the case of Lake Nicaragua, enter the lake through the rivers that connect the lake to the ocean, jumping rapids like salmon on their way to the lake.
Unlike many other fish, the Bull shark has an ability to adjust its body chemistry to fresh water. The blood of all sharks has to be as salty as the water around it, but the bull shark solves this problem through excreting large amounts urine to dilute the salt content.
It is thought that most Bull sharks that travel up rivers are females, looking for a protected place to give birth. Because few ocean predators can follow the bull shark up the river, the fresh water environment is a good place to start a safe nursery.
In the Ganges River, where many pilgrims bathe as part of religious ritual, shark attacks are not unknown. The Ganges also has its own native sharks that use the river, but these are strictly fresh water sharks. Confusingly, this species is officially known as the Ganges shark, which is also the name for the bull sharks that swim up the river.
Attacks on humans
Bull sharks are quite unpredictable and aggressive creatures. Because of their large size and tendency to frequent shallow water and fresh water, this species is considered dangerous to humans. According to the International Shark Attack File, this species is the third most dangerous shark, after the tiger shark and the Great white, based upon attack frequency. However, this species prefers warmer water than great whites and hangs out closer to shore than tiger sharks do. Because a large number of developing countries have warm water coasts and rather poor shark attack reportage, it is possible that there are a great many bull shark attacks that never get into the official files. It is very possible that this species is responsible for more deaths and attacks than the great white.
Some of the attacks on people are thought to come from mistaken identity. The sharks mistake people for fish or young dolphins and attack. This mistaken identity thesis is also posited for other species of shark, including the great white and the tiger shark. However, other factors might be driving the bull shark to attack people.
Bull sharks have the highest levels of testosterone in its system than any other species on land or sea, including bull elephants in must. If one corners a bull shark, it is very likely to respond with aggression. However, this shark is designed to be an ambush predator, with a dark back that is hard to see in murky water. If a swimmer accidentally makes a bull shark feel cornered, the shark could respond with aggression. Because the sharks are hard to see in the water, it could be relatively easy to find yourself in a situation where the shark feels cornered.
A Successful Species
The bull shark is a successful species because of its varied diet and its ability to live in both salt and fresh water. It is a widespread species that is found throughout the tropical and warm temperate seas and estuaries of the world. Because it likes shallow water and fresh water environments, the shark can cause problems with people. However, it is a vital predator that keeps the prey species in the proper numbers to maintain the ecosystem.
We humans have inflicted upon sharks with what can only be described as a disproportionate to their occasional attacks. Now, most shallow water ecosystems have a paucity of large shark species, including the bull shark.
Instead of responding with irrational fear, we should try to appreciate the bull shark as it is. It is a predator that can use both the rivers and lakes and the shallow ocean as its hunting grounds. It is a predator that was here millions of years before we ever walked the earth, waded in the water, cast fishing nets, or went swimming at the beach. It is high time that we showed a little respect to those other predators with which we share the world, not the least of which is the bull shark.