About Sharks
Sharks have prowled Earth's seas, essentially unchanged, for 400 million years. Their size, power, and great, toothy jaws fill us with fear and fascination. And though sharks kill only a few people each year, media coverage and movie portrayals of attacks have marked sharks as voracious killing machines. Our fears—and appetites—fuel an industry that hunts more than 100 million sharks each year and threatens to purge these vital predators from the oceans.
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| shark-attach NGS/Waitt grantee Nick Whitney is using accelerometers to study fine-scale aspects of shark behavior that cannot be observed directly. Understanding reproductive strategies and mating behavior is crucial for proper management of marine fish species, yet very little is known about the mating systems of most sharks. In the few shark species for which it has been observed, courtship and mating has involved unique postures and movements that are likely to be very different from those involved in typical daily activities. A device that records these postures and movements may therefore allow us to identify courtship and mating behaviors in species for which direct observations are impossible. To that end, Whitney has tested the ability of three-dimensional acceleration data loggers (ADLs) to identify mating behavior in adult nurse sharks during their mating season in the Florida Keys at the Mote Marine Laboratory. Whitney and Wes Pratt have been studying nurse sharks together in the Dry Tortugas since 1998. The annual nurse shark mating aggregation in this area has been the basis of a long-term tagging study by Pratt and Jeff Carrier (Albion College) since 1992, and now continues with Whitney and Theo Pratt.  Shark Species
Bull sharks are aggressive, common, and usually live near high-population areas like tropical shorelines. They are not bothered by brackish and freshwater, and even venture far inland via rivers and tributaries. Because of these characteristics, many experts consider bull sharks to be the most dangerous sharks in the world. Historically, they are joined by their more famous cousins, great whites and tiger sharks, as the three species most likely to attack humans. Bull sharks get their name from their short, blunt snout, as well as their pugnacious disposition and a tendency to head-butt their prey before attacking. They are medium-size sharks, with thick, stout bodies and long pectoral fins. They are gray on top and white below, and the fins have dark tips, particularly on young bull sharks. They are found cruising the shallow, warm waters of all the world’s oceans. Fast, agile predators, they will eat almost anything they see, including fish, dolphins, and even other sharks. Humans are not, per se, on their menus. However, they frequent the turbid waters of estuaries and bays, and often attack people inadvertently or out of curiosity. Bull sharks currently are not threatened or endangered. However, they are fished widely for their meat, hides, and oils, and their numbers are likely shrinking. One study has found that their average lengths have declined significantly over the past few decades. 
Sand sharks are brownish-gray with rust-colored spots on top and white underneath. They have a flattened, cone-shaped snout and a distinctive, oblong tail with a notched, upper lobe that is significantly longer than the lobe below. Individuals range in size from 6.5 to 10.5 feet (2 to 3.2 meters) in length. Their name comes from their tendency toward shoreline habitats, and they are often seen trolling the ocean floor in the surf zone, very close to shore. They are found in warm or temperate waters throughout the world's oceans, except the eastern Pacific. Sand tigers are the only shark known to come to the surface and gulp air. They store the air in their stomachs, which allows them to float motionless in the water, seeking prey. They are voracious predators, feeding at night and generally staying close to the bottom. Their staple is small fish, but they will eat crustaceans and squid as well. They occasionally hunt in groups, and have even been known to attack full fishing nets. Although this species is widespread and is not widely fished for food, it has one of the lowest reproduction rates of all sharks and is susceptible to even minimal population pressure. For this reason, it is listed as vulnerable and is protected in much of its range. 
Tiger sharks are named for the dark, vertical stripes found mainly on juveniles. As these sharks mature, the lines begin to fade and almost disappear. These large, blunt-nosed predators have a duly earned reputation as man-eaters. They are second only to great whites in attacking people. But because they have a near completely undiscerning palate, they are not likely to swim away after biting a human, as great whites frequently do. They are consummate scavengers, with excellent senses of sight and smell and a nearly limitless menu of diet items. They have sharp, highly serrated teeth and powerful jaws that allow them to crack the shells of sea turtles and clams. The stomach contents of captured tiger sharks have included stingrays, sea snakes, seals, birds, squids, and even license plates and old tires. Tiger sharks are common in tropical and sub-tropical waters throughout the world. Large specimens can grow to as much as 20 to 25 feet (6 to 7.5 meters) in length and weigh more than 1,900 pounds (900 kilograms). They are heavily harvested for their fins, skin, and flesh, and their livers contain high levels of vitamin A, which is processed into vitamin oil. They have extremely low repopulation rates, and therefore may be highly susceptible to fishing pressure. They are listed as near threatened throughout their range. 
The legendary great white shark is far more fearsome in our imaginations than in reality. As scientific research on these elusive predators increases, their image as mindless killing machines is beginning to fade. Of the 100-plus annual shark attacks worldwide, fully one-third to one-half are attributable to great whites. However, most of these are not fatal, and new research finds that great whites, who are naturally curious, are "sample biting" then releasing their victims rather than preying on humans. It's not a terribly comforting distinction, but it does indicate that humans are not actually on the great white's menu. Great whites are the largest predatory fish on Earth. They grow to an average of 15 feet (4.6 meters) in length, though specimens exceeding 20 feet (6 meters) and weighing up to 5,000 pounds (2,268 kilograms) have been recorded. They have slate-gray upper bodies to blend in with the rocky coastal sea floor, but get their name from their universally white underbellies. They are streamlined, torpedo-shaped swimmers with powerful tails that can propel them through the water at speeds of up to 15 miles (24 kilometers) per hour. They can even leave the water completely, breaching like whales when attacking prey from underneath. Highly adapted predators, their mouths are lined with up to 300 serrated, triangular teeth arranged in several rows, and they have an exceptional sense of smell to detect prey. They even have organs that can sense the tiny electromagnetic fields generated by animals. Their main prey items include sea lions, seals, small toothed whales, and even sea turtles, and carrion. Found in cool, coastal waters throughout the world, there is no reliable data on the great white's population. However, scientists agree that their number are decreasing precipitously due to overfishing and accidental catching in gill nets, among other factors, and they are listed as an endangered species. 
Hammerhead sharks are consummate predators that use their oddly shaped heads to improve their ability to find prey. Their wide-set eyes give them a better visual range than most other sharks. And by spreading their highly specialized sensory organs over their wide, mallet-shaped head, they can more thoroughly scan the ocean for food. One group of sensory organs is the ampullae of Lorenzini, which allows sharks to detect, among other things, the electrical fields created by prey animals. The hammerhead's increased ampullae sensitivity allows it to find its favorite meal, stingrays, which usually bury themselves under the sand. The great hammerhead is the largest of the nine identified species of this shark. It can grow up to 20 feet (6 meters) in length and weigh up to 1,000 pounds (450 kg), although smaller sizes are more common. Found in temperate and tropical waters worldwide, far offshore and near shorelines, hammerheads are often seen in mass summer migrations seeking cooler water. They are gray-brown to olive-green on top with off-white undersides, and they have heavily serrated, triangular teeth. Their extra-tall, pointed dorsal fins are easily identifiable. Most hammerhead species are fairly small and are considered harmless to humans. However, the great hammerhead's enormous size and fierceness make it potentially dangerous, though few attacks have been recorded. Hammerhead populations are not accurately known, but appear stable worldwide, and they are not considered threatened. 
The scientific name for the nurse shark sounds like something Bilbo Baggins might have said to summon elves to his rescue: Ginglymostoma cirratum. Actually the name is a mix of Greek and Latin and means "curled, hinged mouth" to describe this shark's somewhat puckered appearance. The origin of the name "nurse shark" is unclear. It may come from the sucking sound they make when hunting for prey in the sand, which vaguely resembles that of a nursing baby. Or it may derive from an archaic word, nusse, meaning cat shark. The most likely theory though is that the name comes from the Old English word for sea-floor shark: hurse. Nurse sharks are slow-moving bottom-dwellers and are, for the most part, harmless to humans. However, they can be huge—up to 14 feet (4.3 meters)—and have very strong jaws filled with thousands of tiny, serrated teeth, and will bite defensively if stepped on or bothered by divers who assume they’re docile. They use their strong jaws to crush and eat shellfish and even coral, but prefer to dine on fish, shrimp, and squid. They are gray-brown and have distinctive tail fins that can be up to one-fourth their total length. Unlike most other sharks, nurses are smooth to the touch. Nurse sharks are found in the warm, shallow waters of the western Atlantic and eastern Pacific oceans. They are abundant throughout their range and have no special conservation status, although the closeness of their habit to human activities is putting pressure on the species. 
As the largest fish in the sea, reaching lengths of 40 feet (12 meters) or more, whale sharks have an enormous menu from which to choose. Fortunately for most sea-dwellers—and us!—their favorite meal is plankton. They scoop these tiny plants and animals up, along with any small fish that happen to be around, with their colossal gaping mouths while swimming close to the water's surface. The whale shark, like the world's second largest fish, the basking shark, is a filter feeder. In order to feed, it juts out its formidably sized jaws and sucks in everything in the vicinity. It then shuts its mouth, forcing water to filter out of its gills. Everything that remains becomes the giant shark's dinner. The whale shark's flattened head sports a blunt snout above its mouth with short barbels protruding from its nostrils. Its back and sides are gray to brown with white spots among pale vertical and horizontal stripes, and its belly is white. Its two dorsal fins are set rearward on its body, which ends in a large dual-lobbed caudal fin (or tail). Preferring warm waters, whale sharks populate all tropical seas. They are known to migrate every spring to the continental shelf of the central west coast of Australia. The coral spawning of the area's Ningaloo Reef provides the whale shark with an abundant supply of plankton. Although massive, whale sharks are docile fish and sometimes allow swimmers to hitch a ride. They are currently listed as a vulnerable species; however, they continue to be hunted in parts of Asia, such as Taiwan and the Philippines. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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