Living Sanibel: The bull shark
In recent years, the bull shark has replaced both the great white and the tiger shark as the most dangerous shark in the ocean. The reason is simple. The other two sharks prefer deeper, offshore waters while the bull shark spends most of its life in shallow, nearshore waters. It is the only saltwater species capable of living in both salt and freshwater environments. This adaptation has given it access to brackish and freshwater environments that would kill any of the other large shark species. It transitions from saltwater to freshwater through a complex osmotic system. The scientific term for this ability is euryhaline-the ability to tolerate wide ranges of salinity. The American and Indo-Pacific crocodiles have this same ability.
The bull shark inhabits all the tropical and subtropical oceans worldwide. It has also been reported some 2,200 miles up the Amazon River in Iquitos, Peru, and has been observed attacking juvenile hippos hundreds of miles up the Zambezi River in Africa.
Like all sharks, the bull shark seldom attacks people. There are confirmed fatalities in Florida attributed to bull sharks, but these are extremely rare. Your chances of getting hit by lightning are 1,000 times greater, and your chances of dying in an automobile accident are more than 10,000 times greater. When these rare attacks do occur, the bull shark bites but typically does not eat the victim. Only the tiger shark and oceanic white-tip have been verified to eat human flesh. The trouble is with the bull-shark bite itself, which is generally so devastating that without immediate medical attention, the victim bleeds to death.
Worldwide, 100 million sharks are killed every year, most for their fins. These make their way to China where they are the main ingredient in shark-fin soup. This single dish is responsible for one of the most ruthless slaughters of wildlife in the history of mankind. After the fins are removed with a finning knife, the live sharks are tossed back into the sea to drown. Annually, 10 people a year are killed by sharks. The ratio of mortality between people killing sharks and sharks killing people stands today at 10 million to one. This is not a sustainable or an honorable equation. Shark finning, like whale hunting, should be banned worldwide.
Sharks, whales, and dolphins are the ocean’s top predators. They serve a vital role in the food chain by removing the sick, aged, and weak from the species they target. If a sick fish is allowed to survive in a school because there are no sharks available to remove it, the entire school can become sick and the loss is far graver than that of a single individual. Sharks cull the oceans of diseased or infirm animals helping to keep gene pools healthy. Without them the entire marine ecosystem is at risk.
The bull shark is a carnivore. It eats fish, other sharks, rays, and sea mammals including bottle-nosed and spotted dolphins, seabirds, mollusks, and crustaceans. It is sometimes killed by dolphins and killer whales, but a mature bull shark has few wild predators willing to take it on. In the Zambezi River, the Nile crocodile has been known to attack and eat the bull shark.
In the waters along the Southwest Florida coast, the bull shark is common. It can be found in the passes, in the back bays and up the way up the coastal rivers. It roams all the way up the Caloosahatchee River, and in all probability there are bull sharks living in Lake Okeechobee. After all, one was found living in Lake Michigan, having swum there via the Mississippi and the Chicago River.
Tarpon fishermen working off the beaches frequently encounter the bull shark, which is known to feed on exhausted, hooked tarpon. A large shark can generally eat a full-grown tarpon in three or four bites. If you happen to see one being caught off one of a local fishing pier or from the beach, consider yourself blessed. This is a magnificent animal and nowhere near as dangerous as the person who reeled it in.
This is an excerpt from The Living Gulf Coast – A Nature Guide to Southwest Florida by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.