Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Shark Attack Review

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This is the next post based upon a presentation given at the Wilderness Medical Society Annual Meeting held in Snowmass, Colorado from July 24-29, 2009. The presentation was entitled “Just When You Thought It Was Safe to Go Back in the Water.”” The topic was an overview of hazardous marine animals and it was delivered by me. Because of the length of the presentation, I am going to divide it into a four consecutive posts.

First, about sharks and shark attacks:

Sharks are found in oceans, tropical rivers and lakes. They range in size from 10 centimeters to over 15 meters (whale sharks). Approximately 30 out of 350 species have been implicated in human attacks. On average, there are fewer than 100 attacks reported each year worldwide, and less than 10% of these attacks are fatal. Sharks are superbly equipped predators, and can detect motion, chemicals, electrical signals, and vibration in the water, with a sensitivity that enables them to easily hone in on prey. The most dangerous sharks from a frequency-of-attack perspective are the white (“great white”, “white pointer”), tiger, bull, blue, dusky, hammerhead, and grey reef sharks. However, it is important to note that any shark, including the seemingly docile nurse shark, will bite a human if sufficiently provoked.

Sharks appear to have two major feeding patterns – the solitary pattern, in which a single shark attacks, and the “frenzied” pattern, in which a school of sharks become stimulated and from that group emerges an attacker(s). Some sharks can swim at speeds of up to 40 miles per hour underwater in bursts of motion. More than 70% of human victims are bitten only once or twice. Aggression seems to often be directed at a wounded or splashing (on the surface) victim.

The clinical aspects of shark bites include massive tissue loss, bleeding up to and including shock, and subsequent infection. Bites to the limbs are most common. The propensity for infection is great because of contamination with seawater, sand, plant debris, shark teeth, and the bacteria that reside within the mouths of sharks.

The general first aid principles are the same as those for other forms of trauma. These are to control the airway, support breathing, maintain the circulation, clean-trim-rinse wounds, apply appropriate dressings to the wounds, and administer antibiotics when indicated. In the field, depending on the degree of bleeding and remoteness from advanced medical care, bleeding control takes priority. Because the marine environment hosts a number of bacteria and other microorganisms that are not commonly a problem on land. The most important of these, from a human health perspective, are Vibrio vulnificus and Aeromonas hydrophila. In situations where an aquatic-acquired wound is sufficiently severe (particularly in a person who suffers immunosuppression) to necessitate the administration of an antibiotic(s), this knowledge must be taken into consideration. Antibiotics that usually are effective against Vibrio and Aeromonas species include the fluoroquinolones (e.g., ciprofloxacin), tetracyclines (e.g., doxycycline), and trimethoprim-sulfamethoxazole.

The odds of shark attack along the North American coastline have been estimated to be 1 in 5-7 million. The danger appears to be greatest during summer months, in recreational areas, during late afternoon and evening, in murky and warm water, in deep water and drop-offs, and upon surface swimmers. All of these factors relate to the intersection of humans and sharks in the water and shark feeding and attack behavior.

Shark attack prevention is obviously quite important. Here are some important risk mitigation recommendations:

1. Avoid shark-infested water, particularly at dusk and at night.
2. Do not swim with domestic animals in shark waters.
3. Swim in groups; pay attention to your companions.
4. Avoid turbid water, drop-offs, deep channels, and sanitation waste outlets.
5. Do not bleed in the water.
6. Avoid wearing shiny metal adornments that might mimic fishing lures. (This is particularly important to avoid barracuda bites.)
7. Do not carry tethered (dead or injured) fish.
8. Be alert for sharks when other fish in the vicinity act erratically.
9. Do not tease or corner a shark. (This is important for any wild animal, and is particularly important to avoid moray eel bites.)
10. Do not panic or splash at the surface of the water.

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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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