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Smell ya, didn't have to tell ya....

In addition to their sight and smell, Great whites, like all other sharks, have an extra sense given by the Ampullae of Lorenzini, which enables them to detect the electromagnetic field emitted by the movement of living animals. Every time a living creature moves it generates an electrical field and great whites are so sensitive they can detect half a billionth of a volt. This is equivalent to detecting a flashlight battery from 1,600 kilometres (1,000 miles) away. Thus, while a great white's sense of sight is useful, the shark does not depend on it. A shark primarily uses its extra senses (i.e, electrosense and mechanosense) to locate prey from far off. Then, the shark uses smell and hearing to further verify that its target is food. At close range, the shark utilizes sight for the attack. The shark will often in ambush deliver a massive disabling bite and then back off to allow the prey to expire. This tactic allows the animal to avoid combat with dangerous prey, such as sea lions. It also has allowed occasional rescue of humans bitten by the animal, though it appears to attack humans mostly in error.

More on the Ampullae of Lorenzini

The ampullae of Lorenzini are special sensing organs, forming a network of jelly-filled canals found on elasmobranchs (sharks and rays) and Chimaera. Each ampulla consists of a jelly-filled canal opening to the surface by a pore in the skin and ending blindly in a cluster of small pockets full of electroreceptor cells. The ampullae are mostly clustered into groups inside the body, each cluster having ampullae connecting with different parts of the skin, but preserving a left-right symmetry. The canal lengths vary from animal to animal, but the electroreceptor pores' distribution is approximately species-specific. The ampullae pores are plainly visible as dark spots in the skin. They provide sharks and rays with a sixth sense capable of detecting electro-magnetic fields as well as temperature gradients.

The ampullae detect electric fields in the water, or more precisely the difference between the voltage at the skin pore and the voltage at the base of the electroreceptor cells. A positive pore stimulus would decrease the rate of nerve activity coming from the electroreceptor cells and a negative pore stimulus would increase the rate of nerve activity coming from the electroreceptor cells.

Sharks may be more sensitive to electric fields than any other animal, with a threshold of sensitivity as low as 5 nV/cm. That is 5/1,000,000,000 of a volt measured in a centimeter-long ampulla. Since all living creatures produce an electrical field in muscle contractions, it is easy to imagine the shark may pick up weak electrical stimuli from the muscle contractions of animals, particularly prey, on the other hand, the electrochemical fields generated by paralyzed prey were sufficient to elicit a feeding attack from sharks and rays in experimental tanks, therefore muscle contractions are not necessary to attract the animals. Shark and rays can locate prey buried in the sand, or DC electric dipoles simulating the main feature of the electric field of a prey buried in the sand. So don't think you would be able to hide near the botton in the rocks or tall grass if in the presense of a shark thinking "they might not see you". As long as you are breathing and your heart is beating, they know exactly where you are. Scary stuff huh.

The electric fields produced by oceanic currents moving in the magnetic field of the earth are of the same order of magnitude as the electric fields that sharks and rays are capable to sense. Therefore, sharks and rays may orient to the electric fields of oceanic currents, and use other sources of electric fields in the ocean for local orientation. Additionally, the electric field they induce in their bodies when swimming in the magnetic field of the earth may give them electric clues about their magnetic heading. This may be how sharks are able to travel great distances between continents without losing their way in the vast oceans.

Temperature sensing ability

Early in the 20th century the purpose of the ampullae was not clearly understood and electrophysiological experiments suggest a sensibility to temperature, mechanical pressure and maybe salinity. It was not until 1960 that the ampullae was clearly identified as a receptor organ specialized in sensing electric fields. The ampullae may also allow the shark to detect changes in water temperature. Each ampulla is a bundle of sensory cells containing multiple nerve fibres. These fibres are enclosed in a gel-filled tubule which has a direct opening to the surface through a pore. The gel is a glyco-protein based substance with the same resistivity of seawater, and it has electrical properties similar to a semiconductor, allowing it to essentially transduce temperature changes into an electrical signal that the shark may use to detect temperature gradients.

Lateral Line

In Great Whites, the lateral line is a sense organ used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail. Sometimes parts of the lateral organ are modified into electroreceptors, organs used to detect electrical impulses. It is possible that Great Whites can use these organs to detect magnetic fields as well.

Look at the big brain on Brad.....

Despite the common myth that Great White sharks are instinct-driven "eating machines", recent studies have indicated that many they possess powerful problem-solving skills, social complexity and curiosity. The brain-mass-to-body-mass ratios of Great Whites are similar to those of mammals and other higher vertebrate species.

In 1987, near Smitswinkle Bay, South Africa, a group of up to seven great white sharks worked together to relocate the partially beached body of a dead whale to deeper waters to feed.

Sharks have even been known to engage in playful activities (a trait also observed in cetaceans and primates). Porbeagle sharks have been seen repeatedly rolling in kelp and have even been observed chasing an individual trailing a piece behind them. See.....Great Whites have feelings too!


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