It took a while to get around to doing this page. Probably because some questions have no answers, and others are really just triggered by people's primal fears. Look around at all the shark toys little kids have -- shark floats for the pool, shark beach towels, and even shark bathrobes. But once their parents see swimmers or divers heading for the deep blue, there's that three-word question that suddenly becomes universal. In French, it's Et les requins alors?, in Italian it's E gli squali?, and in German it's Gibt's haifische? In English people ask, What about sharks? And the answer: What about them?
What are the chances of being attacked by a shark if you are in the ocean?
If you've been reading this website or other sources, you know the chances of shark attack are very low. There are only between 5 to 10 fatalities a year to humans worldwide, and less than 100 attacks a year worldwide. This includes all species of sharks (350 or more). Think of the millions of people all over the world who "use" the ocean -- beachgoers, divers, sailors, surfers, fishermen. Tiger and bull sharks (free roamers who can also enter inland waters or lagoons) are the source of most attacks on humans, although people seem to fear great whites the most. More than 70 percent of great-white-shark victims survive, because the shark usually lets go, realizing that if their prey is not a source of high energy (fat), it's not worth eating and digesting. As apex (top of the line) predators, great whites are too mighty to exist in large numbers, as the food chain would not be able to support them. It happens that shark attack victims are most often white males between the ages of 18 and 25, and most shark attacks occur in less than 5 feet of water. The reason for this has purely to do with numbers: Shallow water is where people generally are, and most of them are young adult males. People who are shipwrecked usually encounter oceanic white-tips (carcharhinus longimanus), deep-water sharks with fighter-jet-like pectoral fins.
 Great White Illusion by Edgar Mueller (click to enlarge) |
How should ocean users minimize their chances of shark attack?
Group activity is always better than being alone, and some experts advise carrying surgical tubing or some other form of tourniquet. Early morning and dusk is feeding time for much of the ocean, and sharks can confuse swimmers in black wetsuits or the shape of a surfboard for seals and sea lions, their favorite food. Some sharks approach out of curiosity, and biting is the only way for them to explore further. Sharks can see color, and are said to be attracted to contrast. Sharks can scent blood and sense motion from quite a distance and, as scavengers, are alert to anything that smells or splashes like wounded prey. Swimming with a dog is said to attract sharks due to the rapid, jerky movements dogs make when they swim. Swimming with jewelry or shiny watches is not a good idea, as fish of many kinds are drawn to things that flash. Swimming near seal colonies, in murky water, swimming at night or near fishing boats or harbor channels where fish guts may be floating around ... all poor ideas.
 Photo by David Doubilet |
What should you do if you are approached or attacked?
Approach and attack are different things. Approach may result in the shark simply going away, which is what you hope for. Reading any of Ralph Collier's shark sightings pages, you'll see that most sharks do nothing at all. But it's a different story if they do. Quoting Peter Benchley, "No matter how experienced or well trained you are, you can never be completely prepared for the sudden appearance of one or more aggressive sharks. No matter how much we think we know, the truth is, none of us knows for certain what any shark will do in a given situation." Swimmers are told to sock a shark in the nose, punch out its eye, yell aggressively and swim away as they continue to face the shark. Nearly all of this is pretty much impossible, given the incredible teeth so close to the nose and eyes, the muffling of sound in water, and the act of swimming itself (apart from dog-paddling backwards, you would not be able to swim and still face the shark). Sharks like to attack ambush prey from below or behind, so letting them know you know they're there may do the trick.
 A rose for Dave, the day after |
On the other hand, it may not. A meeting with a 4000-pound shark that decides to rush you is a cosmic event. The shark that got Dave Martin in Solana Beach was seen cruising below once, by one person in a group of nine. In spite of the number of people in the water, there was nothing anyone could do. Oddly, sharks almost never attack more than one person in a group, as demonstrated by the Martin incident, but the trauma to those present when such an attack occurs is also tremendous. Perhaps the best thing to keep in mind is the likelihood of ever being in such a situation -- very, very rare. As my friend Jerry says, "I don't worry about what I have no control over." He swims in the ocean all year long, often alone, in a black wetsuit, and for miles at a stretch.
 This sleeping nurse shark allowed itself to be touched (read more here) |
Some sharks like great whites and hammerheads must keep moving in order to stay alive. They are known as obligate ram ventilators because of the need to "ram" or force water (which contains oxygen) through their mouths and over their gills, which is how they breathe. Although it's tough to capture a great white due to its mass, studies done on other sharks show that swimming is orchestrated through an area of the spinal cord (not the brain), which might be the reason sharks can "rest" while still moving.
Other shark species remain stationary for periods of time on the ocean bottom, but do not appear to close their eyes. (A nictating membrane covers the eyes for protection when a shark attacks prey.) And still others appear to have cycles of activity -- active at night, finding rocks to shelter in during the day.
 Shark eggs in casings with tendrils that fasten onto coral or plants for security |
Some sharks lay eggs that hatch in the ocean; others produce eggs that hatch inside the mother, resulting in babies (pups) that are born live. Eggs that leave the mother's body are covered in sacs or hard casings (known as oviparous reproduction) that can attach to coral or plants or even be buried in sediment where the unhatched pups can safely develop. Shark species that are viviparous (e.g., the hammerhead) hatch eggs within the uterus, where the developing young are fed by uterine milk or placenta.
Sharks that are ovoviviparous produce eggs that travel from the ovaries into the uterus where they hatch and the embryos are nourished by yolk. Great whites and mako sharks are ovoviviparous and oophagous, which means that their pups must survive within the womb without nourishment from the mother. What do they feed on? Unhatched eggs or their siblings. Thus biology itself creates a dangerous and competitive "shark-eat-shark" environment for these species even in the womb, which accounts for their resilience and status in the marine food chain and, in the case of the great white, its overall low numbers. Although multiple embryos can hatch, only one or two actually make it from each litter to carry on the species.
Male sharks fertilize females frontally by way of pelvic claspers (extensions of the pelvic fins) that deliver sperm. The females of some species (e.g., blue sharks) have very thick skin due to bites inflicted by males during mating. Shark mating is complex, with congregation rituals in certain species and mate selection in others.
Bony fish (osteichthyes) -- comprising most fish -- have a swim bladder that fills with oxygen and keeps them buoyant. They do not have to swim to breathe. Sharks (in the elasmobranchii group, a subclass of chondrichthyes, or cartilaginous fish) have no swim bladder and must keep moving to breathe; therefore their skeleton is made of cartilage, which is lighter than bone.
 Porbeagle shark skeleton (click to enlarge) Canadian Shark Research Lab |
Bony fish can be compared to blimps or hot-air balloons; sharks are more like airplanes, requiring strong dorsal, pectoral and caudal fins for stabilization, maneuverability and speed. The placement of a shark's fins allow it to stop and make sharp turns -- all part of stalking and surprising prey.
Great white sharks (carcharadon carcharias) are legendary for their rows of replacement teeth that rotate into place when older teeth wear down or break off (click photo to enlarge). In fact, many species of sharks have rotating serrated teeth that are replaced every few weeks. White sharks can break and replace as many as 1000 teeth per year. Unlike humans, sharks' teeth are rooted in their flesh, not the jaw, which is why and how they fall out so rapidly. All sharks, whether filter feeders or flesh-tearing carnivores, have multiple rows of working teeth with many more rows of replacements ready to go. Some sharks (like the sand tiger) have long, pointed teeth to pierce fish and swallow them whole; others have serrated teeth that cut and tear their prey. Some species have both kinds of teeth.
Because their skeletons are made of cartilage, fossilized teeth are generally the only remnants we have of early sharks. Sharks' teeth don't only serve sharks: humans have attached them to implements to create tools of various kinds over the ages.
 Pointed teeth of a porbeagle shark (also oophagous, competing for life in the womb) |
 Tiger shark jaws and teeth (click to enlarge) |
