Sharks have had remarkable evolutionary success. The first sharks lived approximately 400 million years ago, about 200 million years before the dinosaurs. They have survived the reign of the large reptiles by another 200 million years. Go to Shark cage diving for more information.
The International Shark Attack File, which contains data on shark attacks from around the world, reports fewer than 100 shark attacks per year, with about 10-15 deaths each year. In comparison, about 1,000 people die from attacks by crocodiles; 1,500 from tigers, lions, and leopards; and 60,000 from snakebites.
Only about 40 of the roughly 400 species of sharks are documented attackers of humans, although another 20-30 species may occasionally attack humans. The great white shark has been implicated in more attacks than any other species. The tiger shark and bull shark are also known to be particularly dangerous.
In general, however, any shark greater than 2 meters, or 6 feet, in length is potentially dangerous. Exceptions to that rule are whale sharks (the largest of the sharks), basking sharks, and megamouth sharks, all of which feed primarily on tiny plankton.
Sharks normally eat fish, sharks, rays, squid and other invertebrates, sea mammals (such as porpoises, seals, and sea lions), sea turtles, and sea birds.
Sharks have remarkable senses. They have good vision, especially up close, and are especially sensitive to motion and contrast. A shark’s sense of smell and taste is remarkable, with two thirds of their brains involved in processing this information. Sharks also have specialized organs called ampullae of Lorenzini, which detect tiny electrical currents, such as those put out by active muscle contractions.
Shark attacks can be broadly categorized into three types. First, in a “hit-and-run” attack, the most common type, the shark takes a single bite and does not return for more. Experts feel this attack may be because the shark mistakes a human for its normal prey. Secondly, in a “bump-and-bite” attack, the shark bumps the victim prior to returning for further bites.
Thirdly, in a “sneak attack,” the shark bites without warning, and then follows up with further attacks. The last two types of attacks, though less common than the hit-and-run attack, are the source of most severe shark bite injuries and shark bite deaths.
Most people do not know a shark is nearby before an attack. Some people receive only a bump from the shark, which likely occurs when the shark is only investigating what is going on at the water’s surface. Because a shark’s skin contains tiny toothlike structures called denticles, it is as abrasive as coarse sandpaper. Thus, a bumping can result in a significant abrasion (scrape).
Shark jaws contain multiple rows of sharp, serrated, triangular teeth, and are continuously replaced as they shed. Classic shark bites are crescent-shaped. Another common wound pattern is a series of parallel cuts caused by the shark raking its teeth on the person.
Sharks bites can cause massive tissue loss, with a tooth-to-tooth biting force that has been estimated to approach, in the extreme, 18 tons per square inch. Most bites, however, result in cuts that are not deep, or puncture wounds that do not cause blood vessel or nerve injury.
See a doctor for all but minor wounds. The doctor will evaluate the wound for significant damage, such as injury to blood vessels, nerves, or internal organs.
A person may not always know whether the wound came from a shark or another fish, such as a barracuda. Shark bites can be massive with significant bleeding and tissue loss. Refer to Mako sharks for more information.
Bites are often crescent-shaped or appear as a series of parallel cuts. Encounters may result in minor wounds, such as abrasions from a shark bump. Some victims have bone fractures (breaks). Others may carry debris, such as shark teeth fragments, that may have been introduced into the wounds during the attack.
Provide emergency care immediately. Control any visible bleeding by applying direct pressure. Keep the victim calm. Provide warmth, since the victim may be chilled from the water and may be suffering from hypothermia (low body temperature).
All shark bite victims should be evaluated by a medical healthcare provider. If only a minor wound is present, consider washing the wound with soap and water and cover it with a clean dressing and seek medical care.
If there is significant injury, activate the emergency medical system and call 911.
The treatment required will be tailored to the extent of the injury. If there is major injury and the patient has had significant bleeding, the initial medical care will be directed at stabilizing the ABCs (airway, breathing and circulation).
Oxygen may be used, intravenous lines started with fluids and or blood transfusions required. If there is tissue loss or major wound, these may need to be cleaned or debrided (where dead tissue is cut away) in the operating room by a surgeon.
Isolated minor wounds may be able to be treated in the emergency department or a doctor’s office. These wounds need to be cleansed thoroughly to prevent infection. With any penetrating wound caused by an animal bite, debris or foreign objects can be pushed into the tissue and needs to be identified and removed if possible an x-ray may be used to identify such objects.
The healthcare provider will likely exam the wound for type of injury, and look for associated injuries like nerve or artery damage. This may require using anesthetic to explore the wound to its full depth to make certain no deep structures are involved.
The key to preventing wound infections is aggressive cleaning. This can begin at the scene using tap water to irrigate the wound. The healthcare provider may want to further wash out the injured area.
Sutures may or may not be used, depending upon the care provider’s concern about the risk of infection. A wound that is sutured or stitched shut is at higher risk of becoming infected.
Finally, the use of antibiotics prophylactically to prevent infection needs to be individualized for each patient. The doctor must first treat life-threatening injuries. With shark attacks, massive tissue loss or bleeding causes most deaths. The doctor will attempt to stop bleeding by applying direct pressure. IV fluids and blood products will be needed for any major wounds. Visit Dive with sharks for further information.
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