Posts Tagged ‘ampullae of Lorenzini’
Whether you think of Great White Sharks as ferocious or just misunderstood, you have to admit they are exciting animals. Due to their nomadic lifestyle and periodic deep water forays, we have limited knowledge about them, which perhaps adds to their mystique. We do know that these powerful sea-dwellers can grow to over 20 feet and live to upwards of 100 years. They are found in almost all coastal and offshore waters which have water temperature between 54 and 75 °F, with greater concentrations off the coasts of Australia, South Africa, California, the northeastern US, Mexico’s Isla Guadalupe, New Zealand and the waters of the Mediterranean. Their preferred habitat is the cooler, deeper waters of the ocean and the waters around oceanic islands and rocky outcrops where deep water is within easy reach.
Great Whites are truly apex predators. They are capable of sensing the blood of an injured animal from over a kilometer away. Their Ampullae of Lorenzini organ, which enables them to detect and stalk the electromagnetic field emitted by the movement of living animals, can detect movement that generates as little as half a billionth of a volt. Though Hollywood has spectacularly portrayed them as preferring humans for lunch, they actually live on a diet of fatty fish and animals such as rays, tuna, smaller sharks, dolphins, porpoises, whale carcasses, seals, sea lions, and occasionally sea birds. Diving with Great White Sharks is certain to be on anyone’s list of Most Extreme Scuba. So, where can aquanauts meet these beauties eye to eye?
• Farallon Islands, California, USA – The Farrallones are located 28 miles west of San Francisco. A protected National State Wildlife Refuge since 1969, the Farrallones are an important research spot for great whites. These islands are one of the few places in the world where great whites can be observed in predatory attacks upon seals, birds, and sea lions from dry land. But doesn’t getting in the water with them sound like such a better idea? Cage diving is offered from late-September through November. Divers are offered a tank/regulator or a hookah setup. Since random chumming of the water is illegal in the Refuge, operators often pull along seal “decoys” to attract the sharks. It is an amazing day trip from the city, with many of the operators leaving right from the tourist hub of Fisherman’s Warf.
• Isla de Guadalupe, Pacific Coast, Mexico – Guadalupe Island is a volcanic island about 145 miles offshore of Baja Mexico, 200 miles south of San Diego. Due to the remote location of the island, this trip is done via a live aboard operation over multiple days. The island has a dramatic sheer rock wall extending hundreds of feet up into the air, as well as hundreds of feet into the ocean. The islands’ large population of seals attracts the white sharks in large numbers. The rocky outcrops of the islands have dramatic drop-offs around the edges that reach down into cool, deep water, also attracting our toothy friends. Visibility at this site is fantastic, up to 100 feet or more. Also, the water temperature ranges from 67 to 70 F, making it much warmer than some other Great White watching spots.
• Dyer Island, False Bay, South Africa – South African Great White cage diving occurs mainly in False Bay and the Whale Coast. Dyer Island is a small, low, and rocky island located just offshore from Gansbaai in the Western Cape of South Africa. During winter, the warm Agulhas Current sweeps down from the Indian Ocean, meeting the cold Benguela Current, creating a temperate zone just off the South African coast – providing ideal conditions for the Great White Shark in particular. This island serves as a breeding ground for a wide variety of seabirds, while its neighbor, Geyser Rock, serves as a home for a large resident seal population. White Sharks are seen on a regular basis in the channel between the two islands (“Shark Alley”) where they feed on a variety of seals, seabirds, and penguins. As an added bonus, Great White sharks in these waters often display very unusual, but highly spectacular breaching when chasing their prey, which makes for some amazing topside photos.
• The Neptune Islands, South Australia – The Neptune Islands sit on a shelf south east of Port Lincoln off South Australia. Grey granite and coastal loam make up these picturesque islands, which support an array of wildlife, including many bird species, a large colony of fur seals, as well as a colony of endangered Australian sea lions. Known as the place where the hit movie “Jaws” was filmed, the waters around these islands are a natural feeding area for Great Whites. Most shark diving here is done via a live aboard vessel. Operators practice cage diving combined with surface bait to give divers an unforgettable experience, sometimes with more than one Great White in sight at a time. The water is very cold here, but the shark action is definitely hot.
• Lampedusa, Sicily, Italy –Have you swam off the coast of Sicily or found the offshore waters of Nice to be nice? Oh yes, there were Great White sharks there, and you didn’t even know it. Great White sightings are becoming more common in the Mediterranean, where a high concentration of nutrients attracts some of the whites’ favourite snacks: large pelagic fish, dolphins and turtles. There have been numerous sightings of the Whites along the Spanish, French, Italian and Croatian coasts, but by far the largest concentration of the sharks is in the channel between Sicily and Tunisia. As far as I can determine, no one does cage diving here because of the infrequent nature of the sightings. However, there are many dive companies that operate out of Lampedusa, Sicily, which puts you in waters with the highest density of Great White sightings in all of the Mediterranean. Divers have encountered large white sharks while diving in the open sea at Sicilian Channel sites such as Pantelleria, Malta, and southwest Marretimo. Though rare, these experiences are as amazing as you can get: no chumming, no decoys and no cage bars between you and the jaws of the Great White.

Less accurate than a coin flip?
Punxsutawney Phil, America’s most famous rodent weather predictor, saw his shadow last Tuesday, signaling six more weeks of winter. CNN meteorologist Chad Meyers, citing stormfax.com, said Phil is correct 39 percent of the time. The U.S. National Oceanic and Atmospheric Administration goes even further, saying Phil has “no predictive skill.” I propose we replace Phil with his amphibious cousin, Phish, in order to achieve a more accurate weather prediction.
Anglers and scientists alike agree that fish behave differently before changes in weather. They have an incredible array of pressure-sensing systems—such as their ‘lateral line’—that key them in to changes in barometric pressure. Barometric changes can also cause changes in suspended sediment and plankton, which alter a fish’s feeding habits. Light intensity—due to wave action, cloud cover or water clarity—can also have a huge impact on feeding behavior. It’s worth noting thought that fish and other creatures living in shallow water are more susceptible to the affects of changes in atmospheric pressure than their deep-water counterparts.
Sharks too are excellent weather predictors. They have something known as the ampullae of Lorenzini on their snout that contain small electric sensitive cells. Among other uses, these sensors pick up changes in pressure, currents and temperature brought on by weather. For example, Florida summers with frequent hurricanes produce a much lower instance of shark attacks (ex. 2005) in part because the animals head to deeper water for safety.
Even shrimp can be good predictors of prolonged weather changes. Production of farm-raised shrimp usually increases along the Pacific coast of South America during El Niño years. Shrimp like the warm El Niño waters and grow rapidly in the brackish-water environment created by the heavy rains. Wild shrimp reproduce in great numbers during El Niños, so if the shrimp population is up, you may be looking at an El Niño event, rather than just a quick series of passing storms.
So, pick a sea creature, figure out what it’s unique, weather-related behavior is, and then watch it to determine the forecast. How wrong could it be? After all, even a coin flip would achieve more accurate results than poor, fuzzy Phil.