Great Whites May Be Taking the Rap for Bull Shark Attacks
for National Geographic News
|August 2, 2002|
Although shark attacks are uncommon, they creep into the consciousness of many beachgoers throughout the summer season.
What most people have in mind in fears of attack is the large and powerful great white, often mischaracterized as a relentless man-eating predator that lurks near popular beaches.
Fabien Cousteau, the grandson of famed explorer Jacques, thinks he knows what's behind that thinking. "Since 1974, when Jaws came out, almost every shark attack has been pinned on a great white," he said. "Every time you ask someone about sharks, the first thing that pops into their head is the great white."
Now, some experts are suggesting that the great white may not in fact be responsible for many of the attacks pinned on the species. These people say the real culprit behind many of the reported incidentsincluding the famous 1916 shark attacks in New Jersey that may have served as inspiration for Jawsmay be the lesser known bull shark.
In July 1916, it was business as usual at the New Jersey shore. The coast was booming with thousands of vacationers and locals striving to beat the heat. But the summer revelry was shockingly disrupted by a series of five shark attacks that left four people dead in 12 days.
In the days that followed, a 7.5-foot (2.3-meter) white shark was captured off the coast, reportedly with human remains still in its stomach, and many people presumed that a rogue great white was responsible for the deaths.
Nearby residents that had set out to avenge the deaths felt sure that they had their "man-eater." But some people now say that unusual circumstances behind some of the attacks suggest that the predator was a bull shark.
Three of the attacks occurred not in the ocean but in a shallow tidal river named Matawan Creek, about 40 feet (12 meters) wide and 11 miles (17 kilometers) from the open ocean.
Matawan residents were surprised in 1916 to discover the existence of a shark in such waters. Fabien Cousteau said he would be equally surprised to learn that that shark was a great white.
Cousteau believes the evidence in the historic case points to a bull shark. In Attacks of the Mystery Shark, which premiers August 4th on National Geographic EXPLORER, he sifts through some of the clues, and along the way sheds light on a fascinating but little understood shark species.
"The bull shark is an amazing shark in so many ways," Cousteau said. "It can switch from salt to fresh water, which is a rare thing. For most sharks, that would be deadly."
Sharks need salt inside their bodies; without it, their cells can expand and possibly rupture, leading to bloating and death. If most sharks, including great whites, enter freshwater, their internal salt levels become diluted.
Bull sharks have special physiological features that enable them to live in freshwater. A gland near the tail helps them retain salt, and the kidneys are designed to recycle the salt already in the body.
So it may have been a bull shark in Matawan Creek that took the lives of Lester Stilwell and Stanley Fisher.
Shark expert Scott Davis, who tracks the movements of great whites, said he doesn't know what the salinity level of the creek was in 1916, but the presence of a great white in such an area would be unusual.
"In my tracking studies, I've never noticed great whites going upstream," he said. "There are a number of places on the West Coast where they inhabit right at river mouths, but whether they go upstream no one knows. My perspective is that great whites would not be able to tolerate a freshwater environment at all."
Bull sharks, in contrast, have been reported in waters thousands of miles up the Amazon River in Peru and in the Mississippi River as far north as Illinois. There is also a population of the sharks in Lake Nicaragua, which because of its great distance from the ocean was once thought to be landlocked.
Sharing the Water
Bull sharks, which are generally about 7.5 feet (2.3 meters) long and up to 285 pounds (130 kilograms), are big eaters. Their diet consists primarily of bony fishes and small sharks, including young bull sharks, but they have been known to feast on everything from seabirds to dogs.
That appetite could spell trouble for humans who enter the same coastal and freshwater areas as the sharks.
"Bulls have a certain pattern of survival, a way of doing things, that happens to overlap with the way people encroach on their realm," Cousteau said. "Bathers are in shallow, warmer coastal waters where these sharks are living. It's amazing that we don't have more instances, and it just reconfirms that they really aren't interested in us and usually an attack is a mistake."
Last summer a bull shark was involved in a highly publicized incident in which a shark severed a young boy's arm. But experts say bull sharks aren't inherently violent toward humans, and in some environments are even docile. In the clear waters of the Bahamas, for example, divers regularly interact with crowds of bull sharks.
Some researchers speculate that this non-threatening behavior may be because the sharks can clearly see people and recognize that they are not a typical food source. By such reasoning, incidents in murkier waters, such as Matawan Creek, might be regarded as cases of mistaken identity.
Whatever the motivation, shark attacks on humans are relatively rare. According to the International Shark Attack File (ISAF), hosted by the Florida Museum of Natural History, there were 76 unprovoked shark attacks and five fatalities worldwide in 2001, a fairly typical year.
Cousteau said lack of caution in human actions often contributes to the shark attacks that do occur, such as swimming at dusk or dawn, splashing in murky water, and entering known feeding waters or areas where people are fishing or chumming.
"We pin the few shark instances that occur around the world on the sharks," he mused, "and never on us for maybe putting ourselves in bad situations."
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