THE JOURNEY

Today's modern sharks started their evolutionary journey about 400 million years ago during what paleontologists refer to as the Devonian period. Just as the earth has been shaped and reshaped over countless millennia, so have sharks. From their ancient ancestors, one species, which had pectoral fins shaped like wings, to modern oddities like the Hammerhead Shark, all have evolved with purpose and design to help them conquer their environment.

Along the Pacific Coast of North America there are about 35 species of sharks that are indigenous or that have been reported from this geographic area. Of these 35 species, about a dozen are considered potentially dangerous to man. They are: Sevengill Shark (Notorynchus cepedianus) , Blue Shark (Prionace glauca) , Sixgill Shark (Hexanchus griseus) , Scalloped Hammerhead (Sphyrna lewini) , Common Thresher Shark (Alopias vulpinus) , Smooth Hammerhead (Sphyrna zygaena) , Shortfin Mako (Isurus oxyrinchus) , Tiger Shark (Galeocerdo cuvier) , Pacific Angel Shark (Squatina californica) , Soupfin Shark (Galeorhinus galeus) , Oceanic Whitetip Shark (Carcharhinus longimanus) and the White Shark (Carcharodon carcharias) - frequently referred to as "The Landlord."

These 12 species of sharks have either been positively identified, or are highly suspect, in one or more unprovoked shark attacks against humans worldwide. During the Twentieth Century 108 shark attacks were authenticated from the Pacific Coast of North America, with the White Shark being implicated in 94 (87%) of the 108 incidents. Since the majority of shark/human interactions from the Pacific Coast involve the White Shark- and because it is the only species that has been implicated in such interactions with surfers- we will focus on that particular species.

My colleague and friend, R. Adian Martin of ReefQuest Shark Research Centre, believes the modern White Shark first appeared about 8 to 10 million years ago. It is thought to have co-existed with the giant prehistoric shark, Carcharodon megalodon, which some paleontologists believe became extinct 2 to 3 million years ago. During their evolution, sharks have developed a battery of sensory systems that is unequaled in nature. It is these sensory systems that drive the animals to do what they do best: Survive over millennia.

As humans, we perceive and interact with our environment using our five senses: Smell, tactile, taste, auditory and vision. These senses have evolved during our species climb up the evolutionary ladder, which doesn't amount to even 2% of the shark's evolutionary reign, i.e., our 5 million years versus their 400 million years. As a species, humans are mere infants when compared to sharks.

THE SHARK'S SEVEN SENSES:

VISION
The structure of the shark's eye is very similar in many respects to that of a human. Many species of shark have a nictitating membrane that acts like our eyelid to protect the eye from injury. Those species that do not have this membrane will frequently roll their eyes back in the sockets for protection, as does the White Shark. In the case of the White Shark, their ratio of rods to cones in the retina are comparable to those of a human. It is conjectured that their visual acuity and ability to see colors is comparable to a human's. To assist them in their nocturnal movements, most sharks- including the White Shark- have specialized cells in back of the retina that aid in night vision. These cells, the 'tapetum lucidum,' reflect light back through the retina thereby increasing the visual image to the shark. A more common example of this specialization can be found in the reflection seen from a cat's eye at night. Their visual acuity allows a white shark to investigate its environmental surroundings day or night. Of greater concern is the white shark's ability to clearly observe the silhouettes of surface objects from far below the surface in clear water conditions. This ability, coupled with their coloration, makes them a 'finely tuned' stealth predator that is difficult at best to observe from the surface.

AUDITORY
The shark's ear provides sensory input from both sound and low frequency vibrations through the cartilaginous skull. The inner ear's structure and contents is thought to permit the shark to determine and distinguish sounds and the geomagnetic fields of the earth's magma. It is believed that the composition and placement of these structures provide direction of a sound origin to a swimming shark. So beyond having an advantage of seeing a surfer before he/she spots the shark, additionally a shark can hear sounds, e.g., paddling, splashing, etc., made by a surfer. Occasionally, surfers jokingly make seal calls while in the water. This signal alone could attract a nearby shark to investigate the origin of the sound. Vibrations produced by these calls could resonate through the surfboard into the water and act as a homing signal for a shark that might be cruising in the immediate area.

TASTE
Taste buds are numerous on the tongue and inner lining of the throat in the White Shark. Their function, as with humans, is to provide the shark with the flavor (taste) of the object, as well as its texture. There does not appear to be other sensory functions other than taste that the cellular lining of the throat and tongue provide to the shark. The extent of this sensory system's control over the shark's diet is still mostly conjecture and is still under scientific investigation. Whether a white shark learns after it has bitten a surfboard, or other non-food item, not to investigate or attack a similarly shaped target in the future is unknown at present. Although, field experiments conducted with white sharks have shown what has been perceived by my colleagues to be learned reactions to specific targets by the sharks.

SMELL
Sharks have long been referred to as the 'swimming nose.' Laboratory experiments have determined that some sharks can detect molecule concentrations that are one part per millions of parts of seawater. Although the specific acuity of the White Shark olfactory system has not been experimentally determined, based on the work of neurobiologists, it appears to be substantial. R. Adian Martin, of the ReefQuest Shark Research Centre, believes the White Shark might have the most sensitive olfactory system of any modern shark species. This sensitivity could provide a means to track a dead whale's scent from miles away or find a pinniped rookery or haul-out site from their excrement droppings carried by the oceans currents.

The effects of human blood on white sharks has not been determined experimentally, although, it would not appear to be a motivator of aggressive feeding behavior based on this specie's reactions to large quantities of human blood that has been present during and following their attacks on humans. However, it is better not to tempt fate, so it is recommended that you exit the water immediately should you receive any injury that results in an open wound.

TACTILE
Lacking hands to hold and fingers to explore objects, sharks must use their skin, fins, and mouth to sample and explore unknown objects in their environment. It has been suggested that White Shark teeth are used in the same manor as a human uses their hands to determine texture of an object. It is not uncommon for a White Shark to rub or bump a boat, surfboard, or other inanimate object in order to determine its texture. This type of behavior could be a precursor to dentition examination of the object in question. If the teeth were texture sensitive, it would explain some, but not all, of the dietary preferences of White Sharks. The hypothesis that White Sharks reject low-caloric food for their preferred high-caloric, blubber-rich marine mammals, does not explain the number of sharks, rays, cetacean, and fishes found in adult White Shark stomachs. Although marine mammals would appear to be at the top of the preferred prey list, a White Shark's dietary preference might be determined more by availability of the prey in question, rather than fat-content.

VIBRATIONS
Sharks have a lateral line that is similar to that of bony fishes. It runs the length of their body, from the tail (caudal fin) along the side up to the head where it becomes more highly specialized. This specialization in the region of the head will be discussed in the next section. The lateral line is composed of openings on the outer skin (pores) that extend into a series of tubes and cells that are lined with cilia and located below the epidermis. Vibrations like those produced by a struggling fish, travel through the water making contact with the lateral line. These vibrations then stimulate the cilia, which transmit a nerve impulse to the brain informing the shark of the location of the source.

This sensory system could cause a White Shark to be attracted to a sport or commercial diver who is using a regulated air supply… or even to a surfer whose board is producing a 'humming vibration' from a skeg that is not aligned properly. Low frequency vibrations that are inaudible to humans are easily detectable by sharks. Other examples of those activities that might produce such a signal to a white shark could be: A leash dragging in the water behind the board while paddling at low speeds or on a wave at higher speeds, exhaling bubbles underwater right before surfacing after duck-diving or a wipeout.

ELECTRORECEPTION
Finally, the remaining sensory system - one that is unique to sharks - is electroreception. This sense is probably more important to the shark's survival than its ability to feel vibrations through the lateral line. Although the shark's electroreceptor, Ampullae of Lorenzini, is an extension of the lateral line, its function is of greater consequence to sharks than the ability to feel vibrations. The ampullae are located throughout the region of the head, but they seem to be more richly distributed on the underside of a shark's snout or nose. (See photos above).

These pores are filled with a jelly like substance and are lined with cilia that are sensitive to minute electrical charges. This sensitivity has been experimentally calculated to be about 25 million times greater (in sensitivity) than that of a human. A shark cruising just above the bottom can easily detect the electrical energy emitted by a benthic (bottom dwelling) fish buried in the sand. This specific hunting behavior has been observed in the Hammerhead Shark and is also thought to be very beneficial to juvenile White Sharks. Juvenile White Sharks seem to prefer close inshore benthic fishes, such as: Halibut, Round Stingrays, Croaker, and other smaller benthic sharks, like the Dogfish.

CONCLUSION:
The White Shark that is frequently observed off our beaches is not an anomaly, nor is it hunting humans. It is a highly specialized apex predatory that can detect our presence long before we are ever aware of its presence. If humans were a primary food source of White Sharks there would be nothing we could do to avoid such an event except to stay out of the water. Their infrequent attacks on humans are usually not predatory. They appear to be a form of investigation, which would seem to be supported by the statistic that less than 9% of their attacks on humans are fatal. Granted these are not the best odds in the world, however, if the White Shark were truly hunting humans the percentages of survival to fatal attacks would probably be reversed with only 9% of the victims surviving. This fact, however, does not mean we should think of sharks in general, and White Sharks specifically, as a family pet or something to be toyed with. They can inflict a serious, and sometimes fatal, injury and should be treated with respect.

When the total number of shark/human interactions for an entire century is considered, there would seem to be little doubt that these incidents are rarer than almost any other hazard that humans face in their daily lives. The number of surfers, divers, swimmers and kayakers that venture into the waters of the Pacific Coast annually are incalculable - certainly in the tens of millions for California, Oregon, Washington, British Columbia and Alaska. Considering that there is on average only 2 interactions (attacks) per year between a shark and human for this geographic region, this statistic speaks volumes on the rarity of these incidents.

Enjoy the beauty and bounty of our oceans, but please do so with respect for its inhabitants. We only have one planet and its survival, and ours, is dependent on the health of its oceans- and that health is dependent on you and me.

Buy Ralph Collier's newly-released book "Shark Attacks of the Twentieth Century- from the Pacific Coast of North America" at Amazon.

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